RFM12 Tutorial – Part2

rfm12b-3dmodel

Part 2 – RFM12 Hardware Interface

In this next part of the RFM12 tutorials I’ll be covering the hardware interface, signal descriptions and how you go about hooking it up to the MCU of your choice.

Packages

The RFM12 RF module comes in a couple of different packages, DIP and SMD, I’ll mainly be covering the DIP throughout these series, but will touch on the SMD where necessary. There is also a long range version of the , this is the and has a reported range of 3000m. The only comes in an extended SMD package, but I won’t be covering it here in the tutorials, although all of the commands will be the same. The only difference is the has an on board power amp, which requires 12V to power the PA portion and has associated control pins for Tx/RX control.

DIP

The DIP package uses a 6×2 2mm pitch header to connect the various signals to the MCU, The size of this header is a bit of a problem if you want to do prototyping as it doesn’t breadboard well, initially I didn’t have any 2mmm pitch female headers so I hand soldered on individual wires to the back of each pin, not really good in the long run as the wires kept on breaking off, so I designed a breakout board to bring out all the signals onto a standard 100mil pitch, much easier to breadboard.

SMD

There are two version of the SMD module, and from what I can gather the only difference is the crystal, one is the standard HCU form factor, while the other is a ceramic oscillator.

Antenna: The only real difference when using the SMD over the DIP package is there is no on-board antenna connection, the antenna comes out via one of the pins, so you need to design in an antenna connection if using the SMD version.

ARSSI: The SMD package allows access to another useful signal that is not available to the DIP version, this is the ARSSI – Analogue Relative Signal Strength Indicator, which is basically the strength of the signal being received by the module, however it’s not bought out on any of the pins, beats me why? There a digital version of this signal accessible though the software interface, from what I can gather there is a difference from the Digital and Analogue versions of this signal. Anyway what it boils down to if you want to access this analogue signal then you have to manually solder on a wire to access this pad (shown as red circle).

UPDATE:  the onboard DRSSI is a single bit returned in the status word that indicates if the RSSI is above the set threshold.   The ARSSI hack mentioned gives an analogue value that is proportional to the RSSI signal received.

ARSSI Connection

Antenna

The antenna mostly used will probably be a whip antenna, basically a piece of wire cut to the right length, I won’t be covering antenna theory here, as I don’t know it ;), but suffice to say the approx lengths involved are as follows (measured from factory supplied antennas):

433Mhz – 173mm

915Mhz – 87mm

UPDATED: 03/07/2009

These antenna lengths are calculated for the respective bands

433 1/4 wave = 164.7mm
433 1/2 wave = 329.4mm
433 full wave = 692.7mm

868 1/4 wave = 82.2mm
868 1/2 wave = 164.3mm
868 full wave = 345.5mm

915 1/4 wave = 77.9mm
915 1/2 wave = 155.9mm
915 full wave = 327.8mm

With these lengths I’ve had no problem reaching 30m+ indoors through a number of walls and 120m+ outside, I’ve not yet trie different types of antennas such as SMA connected rubber duck type but they should work as I’ve spoken to tech support at HopeRF and they tell me that the antenna circuit on both modules is balanced to 50 Ohm, this means that most SMA rubber duck antennas in the right frequency range will also work. Make sure that the antenna is matched to the frequency range required to get the best range, i.e. don’t use a wifi antenna for 2.4GHZ on a 433Mhz module, it may work for short distances, but definately won’t be optimal for long distances, also you may damage your RF module (unconfirmed it this is is the case as these are low power devices), but usually antennas need to be SWR matched to stop reflectance back into the transmitter circuit.

There is also some technical documents on Hopes website for PCB based antennas, but I’ve not used these at all so your milage may vary with them.

As mentioned earlier the SMD has no direct antenna connection so you need to design in a connection, either a solder pad on your board or an SMA connector.

The DIP package on the other hand allows you to solder in the antenna right onto the module, usually you will solder in the wire directly, however you need to make sure that you get the right pad, as there are two very small solder pads right next to each other, one is the antenna, one is ground, both are not marked in anyway as to to their function, and the documentation does not show which one is which. You need to solder in the piece of wire to the one not connected to ground, best to check with a multimeter or continuity tester first.

It looks as though you can also uses these two pads on the DIP module to connect an external SMA connector with a pigtail to the module as well (both ground and antenna).

PIN Connections

The pin connections for the module is described below, I have indicated whether the connection is required or is optional when making connections. The basic connections as described will allow data rates of up to approx 12000bps on an 8Mhz PIC using a bit-bashed SPI, polled approach when handling sending and receiving data, higher data rates will require hardware SPI, higher MCU speed and the use of interrupts, these will be discussed in a later .

UPDATE:  Please see this article for more detailed information regarding RFM12B bit rates and the different pin connections.

VDD (required) – The nominal working voltage is between 2.2v and 3.8v (NOT 5V), make sure that you have bypass filters in place on the supply rails.

nINT/VDI (optional) – This pin can be configured as either input or output, if configured as an input then it’s function is an active low interrupt request from the MCU, The MCU pulls this line low if it want to interrupt the RF module.
If configured as an output then its the VDI, Valid Data indicator, meaning valid data has been detected by the receiver and outputs a high. Factory Default is VDI

SDI (required) – SPI Data input, where the MCUs MOSI signal needs to be connected to.

SCK(required) – SPI clock input from MCU

nSEL (required) – Chip Select (active low). This signal must be pulled low before any signal is sent via SPI to the RF module,

SDO (required) – SPI Data out, where the MCU MISO signal needs to be connected to.

nIRQ (optional) – Interrupt Request output (active low), this is when the RF module wans to signal the MCU an event has occurred. This should be tied high with a pullup resistor.

FSK/DATA/nFFS (optional but requires 10K pullup when not used):
FSK – Transmit data input
DATA – Received Data output
nFFS – If pulled high then the FIFO is selected then data is transmited / received via the internal FIFO acessed via the SPI interface. If the FIFO is not being used then this is where the data is directly clocked into or out of the Tranceiver. Use this mode for high datarates.

DCLK/CFIL/FFIT (optional):
DCLK – is the data clock when no FIFO is used (used in conjunction with FSK/DATA/nFFS pin).
CFIL – is used to connect an external capacitor when using 256K datarates, this is for the analogue filter, normally the internal digital filter is used by default, only lower data rates are achieved with the digital filter.
FFIT – FIFO interrupt, interrupt signal is generated whenever the FIFO interrupt level is achieved (level is configured via SPI and is covered in the software interface tutorial), normally the interrupt level would be set to 8 if using the FIFO so that an interrupt is generated for every byte received. If using the FSK/DATA to clock in the data then the interrupt level should be set to 1, this way an interrupt is set for every bit sent/received.

CLK (optional) – Clock output, defaults to 1Mhz, but can be configured in increments up to 10Mhz, or switched off. This signal can be used to provide a clock signal to the MCU if it has no internal oscillator, i.e. cuts down on an additional crystal required for the MCU. This signal is also used in the calibration of the RF modules and will be explained later.

nRES (required) – this is reported in the Hope RF documentation as an output but is really an input (active low) and needs to be tied high at all times. If pulled low it will reset the module back to POR default (power on reset) settings.

GND (required) – Power Ground.

ANT (on SMD, required) – Where the antenna is connected.

Back – Part 1 | Next – Part 3a

129 thoughts on “RFM12 Tutorial – Part2

  1. Hi,
    second part is also gr8. It help to clear a lot of concepts. waiting for the next part.Hope the controller u will use is AVR and programming will be in C language. 🙂

  2. Hi,
    Stephen. Finally i have transmitted the data sucessfully using RFM12BP. i am reciving the data on hyperterminal of my pC. but there is still a small problem that is if I send numbers in sequince i.e from 1-9 it recives the odd numbers first and then the even one. i donot know y is this hapening if u can help me out with this problem .I know u will have some gr8 ideas for solving this problem. Thanks a lot dear.

  3. Well done! Please send me your code if possible, I would love see it.

    The only thing I can think of is the TX levels maybe causing problems. How are close are the two units? The RFM12BP is for ranges up to 3000m so you may have to drop the Tx power right down to minimum and the Rx sensitivity down during development.

    Are you doing any error checking with your packets? Such as CRC or a checksum? That way you can be sure that the packet you sent is the packet you received.

    Also you may have to look at some forward error correction such as a hamming code, but I would not have thought it was needed for such small data streams.

  4. Hi,
    Thanks for ur appreciation :)and useful tips too. My code is nearly same as the one given in the programming guide. if u still need give me ur mailing adress. the two modules are kept closer so,I think ur right I have to reduce the power. Also on some other website I have studied that these modules have no internal error correction and they say something about the SNAP protocol. Do you have any idea abt it? if any plz do share how to use this protocol with these modules. Thanks.

  5. None of the RFM12 modules have error correction, so you need to build that into you application. Just a basic CRC or checksum while testing should be ok, all depends on you application.

    1) Build your packet
    2) Do a checksum of everything, but not the sync or the preamble.
    3) Add this calculated checksum to the end of the packet.
    4) Transmit the complete

    5) On the receiver you receive the packet containing the data and checksum
    6) recalculate a new checksum on the received data using the same formula you used on the transmision side. Don’t include the received checksum in this calculation only the data.
    7) if the calculated checksum and the received checksum are the same, then more than likely you have a good packet, if not then you have a corrupt packet and you either ignore the data or get it resent.

    The snap protocol you are referring to, is S.N.A.P and is found here http://www.hth.com/snap/ this defines a simple network addressable protocol.

  6. Just a note to thank you for these tutorials. After a couple of hours of coding and reading I have managed to get two of these devices communicating effectively.

    Many thanks again.

    Stephen (UK)

  7. *reSpawn

    Good question, I’ve only used the RFM12B variety, but from the looks of the data sheets you’re right, it only looks like a VCC difference. Even the chip programming guides looks the same.

    Anyway I’ve asked just sent an email off to HOPE so “Hope”fully I’ll get a reply (lol sorry about that)

  8. Hi
    My name is nithin prakash, i recently started to work on RFM12BP, i have just established communication b/w RFM12BP modules. I have a doubt in the Power amplifier section. To the VCC-PA pin i have an input of 12V from a DC power supply. For the RF module that i am designing i want to give it a 5V supply, so know i am planning to introduce an voltage booster circuit i.e. 5v to 12v(say max1771). But if i connect a ammeter in series with the power supply the current drawn by the VCC-PA pin is at 0mA or 0A. I am doing continuous transmission for 10 seconds. The current consumption of the power amplifier is vital for the selection of voltage booster.
    Thank you in Advance….

  9. Hi
    My name is nithin prakash, i recently started to work on RFM12BP, i have just established communication b/w RFM12BP modules. I have a doubt in the Power amplifier section. To the VCC-PA pin i have an input of 12V from a DC power supply. For the RF module that i am designing i want to give it a 5V supply, so know i am planning to introduce an voltage booster circuit i.e. 5v to 12v(say max1771). But if i connect a ammeter in series with the power supply the current drawn by the VCC-PA pin is at 0mA or 0A. I am doing continuous transmission for 10 seconds. How can the current consumption be at 0A or 0mA?. The current consumption of the power amplifier is vital for the selection of voltage booster.
    Thank you in Advance….

  10. Hi
    I am looking into the RFM12B whether it is suitable for our project.This article helps me a lot.I have one question….

    If my controller dose not have SPI interface means,How can I use RFM12B?

    Please can any one help me?…

  11. thank you for your great tutorial. i cannot wait to see the next part. i am now working on this RF as well. and i think i did something wrong. will i burn the RF if i power it up as Vdd=5? and another question is do i need to connect a decouple capasitor to the antenna?

  12. I have run the RFM12B at 5v with no apparent problems, however it is out of spec / at the upper limit so I wouldn’t run it permanently. The RFM12 is the 5V version.

    No decoupling capacitor is required. The antenna is matched for 50 Ohms so it can connect directly to SMA or whip antenna (i.e. piece of wire at correct length)

  13. oh~~ thank you for your reply. now i have felt much much better from worrying of burning all my buddies.
    if so i think i have made the correct connection for the hardware. then the problem should dues to the software. so,stephen, have you tried the example 2 in the programming guide, since i use PIC16F877A. does this example have the same bug as example 1?(such as changing 0x82D8 to 0x8299).
    and aspire for the part 3. they are great.

  14. Hello everyone. I recently bought the RFM12BP modules. Haven’t tested them yet. I am trying to get as much info as I can first. The BP type is different with these RX/TX Enable pins from the P version. What are these pins for when I can control the RX/TX functionality with software? Do I have to controll these pins (two pins more on micro), or can I just pull them both high? Great tutorial btw. Thx.

  15. Hi Budilm,

    Basically the RFM12BP is an RFM12B with a Power Amplifier added, this gives the extra range, and is also why it needs 12V and the control pins. You must control the pins when ever you Tx or Rx so yes you do need to have additional I/O control them via your driver software.

  16. Hi Stephen,

    thank you for the reply. I found this info: http://micropet.me/blog/?p=5
    Down there is a schematic of his board for the RFM12BP module. If you take a closer look you will find, that he simply pulled both controll pins for the RXEN and TXEN high. I wrote him a message but he did not reply yet so I dont know if it works. He writes also that the power amplifier section works with supply voltage from 0,5 to 13V but in the datasheet is 11V to 13V. Because I want to power my application from 3s LiPol battery (Voltage ranges from 9V to 12,5V) I am curious if the power section will still work with 9V? What do you think?

  17. Hi, i just receive my RFM12 yesterday. Your blog have some good information. I’ll try to connect it with arduino, do you have some information about it?
    Thanks

  18. Stephen
    for 915MHz, what is the correct antenna length?
    You mentioned above is 87mm, but according to antenna length calculation, it is 77.949mm.
    Tks.

  19. @bennyjo

    The lengths I quoted I quote are from direct measurements I made of the antennas sent from HopeRF with the DIP version of the module. I would go with the calculated length over the measured one.

  20. Stephen
    I am trying to use the ARSSI signal from the RFM12 as a type of rangefinder – your picture is a really good start. My RFM12 is slightly different – in this area (red circle) on my RFM12 I can see only an SMD resistor and a via-both alternate about 0.47V and aboüt 0.54V to ground when receiving an intermittant text string. What did you solder to to get the signal out? (Do you have a hires version image of this area on the module?)
    Thanks

    Martin

  21. @Martiv_v

    The picture was sent to me by HopeRF when I asked the question regarding how to access ARSSI (thinking it was as simple as accessing the value via an internal registers) so I’ve not used it as yet.

    Sorry but I don’t have a higher res photo, but looking at mine in front of me, it looks the same as yours, I have a resistor and a via, that is the same area in the photo in the photo.

    I’ll contact Hope and see what their response is.

  22. I’ve also 4 RFM12BP modules and connected them to an Attiny2313 to send some data received from the serial port. My 2313 controls the data with the RFM12bp through SPI, just like in the example code. I`ve connected NIRQ,SDO,NSEL,SCK,SDI to my microcontroller.
    When I powerup everything exept for the VCC-PA, I can see in an RF monitor that the module sends something at low power. But when I connect the VCC-PA pin to 12V, I expected a much higher RSSI value. (whithout +- -52dB with -42dB, transmitter and chipcon receiver both on same desk) but a much higher problem is that my power transistor on the module becomes very hot when the 12V is connected. Is somebody familiar with this problem? Can anybody show how the module should be connected when SPI mode is used?

  23. Stephen

    Some feedback to the ARSSI signal: I wired the resistor pad as you suggested to an ADC (Mega32) and I get a pretty stable signal- (but only when I do the ADC sample right in the middle of the receive code loop- otherwise the signal is basically 0). At -21dB transmit power the raw ADC value (ref. 5V) ranges between 450 directly next to the transmitter and maybe 150 at about 20m range- so from ~2.2V to 0.73V. (reception cuts out at less than this.)Will see how this can be used for rangefinding in practise.

    Thanks for the help

    Martin

  24. @Martin

    Ahh makes sense, I had actually wondered about this some time ago about the timing of reading the aRSSI in regard to Reception (as one does while lying in bed at 3am unable to sleep)

    When are you doing the ADC reading, just before/after you process a received byte? or when you receive the INT from the RFM12?

    Stephen…

  25. Stephen,

    I have been using a modified version of the original code from Benedikt K and the BASCOM version from Joachim Fossie Bär Reiter (http://www.mikrocontroller.net/topic/67273- a German site). The relevant section looks like this:

    Sub Rf12_rxdata(byval Maxchar As Byte)
    Temp = Rf12_trans(&H82c8)
    Temp = Rf12_trans(&Hca81)
    Temp = Rf12_trans(&Hca83)
    For Count = 1 To Maxchar
    Rf12_ready
    Temp = Rf12_trans(&Hb000)
    Arssi = Getadc(0) ‘measure received signal strength in the middle of the receive loop

    Rfdata(count) = Temp
    Next Count
    Temp = Rf12_trans(&H8208)
    End Sub

    So basically just after the transfer. This code uses only the 4 SPI lines – no interrupts- but works fine for low rate transfer.

    Martin

  26. Hi StephenS
    i m aamir i hve been workin on RFM12B module for the last six months.I first used AT89S52 controller and it worked fine.The RF was configured with some difficulty,Now i m using PIC16F726 but there is some trouble in communication with the RF via SPI.The controller is not communicatin with the RF and configurin it.I hve read urs code.i hve a simplified code written using the sample code given by HOPE RF for PIC.But tht code is not workin.I hve tryed alot but no succeess.The WriteCMD() function as written by u too in which u hve optimzed NOP() delay thts i think creatin problem.Do u hve problems with it too.Can u help me some how
    thnxs

    1. @Aamir

      Have you tested the SPI to see if commands are getting through?

      I test by hooking up a frequency counter or oscilloscope to the CLK and then I send through a change frequency command for the CLK. If that works then at least I know the SPI side of things is working. A point to remember is make sure that the SPI is within the specified frequency, I think is < =2.5MHz. If too low then you also may have problems. Stephen...

  27. hi
    thnxs for reply.
    I hve solved the problem the PIC pins are mulitipurpose and i thought tht by default these pins will work as I/O but the pins to which i connected nIRQ and FFIT were workin as A/D converter input.so i hve make the correction and its workin well now.
    Can u tell me tht how u calculte the reciever bandwidth and how much deviation is good.Do u use the carson’s rule.There is a table i can see with different data rates and deviations and receiver bandwidth How u hve build it.
    thnxs

  28. @aamir

    Great to hear.

    In the latest series on the RFM12 Tutorials – Part 3a (http://blog.strobotics.com.au/2009/07/27/rfm12-tutorial-part-3a/), I’ve put up a table with values that I’ve gleaned from data sheets, both from HopeRf and Integration, before they were purchased by silicon Labs. These values seem to work well, but I’m sure could be optimised further.

    I’ve never heard of Carson’s Rule, but am about to research it 🙂

  29. @Stephen

    thnx buddy
    yeah Carson Rule is used to calculate the Bandwidth of FM signal as well as FSK.And i hve learned tht for proper reception the signal bandwidth should be same as tht of channel.So to configure the receiver bandwidth i use Carson rule.Its works but as u gona know the receiver bandwidth in urs table didnt match as they are must less than we get usin this rule.i hvent tested urs table yet but i believe in urs words.i will test then later and i hve read urs articles as well as all the data sheets i duno about the updated datasheet i will check it out and i appreciate urs efforts

  30. Hi,

    I finally managed to connect and programm my module RFM12BP. But I have a problem. I connected the RFM module through 5cm long cables to my microcontroller board. Now when I select output power higher than the lowest setting, I get interference on the microcontroller inputs. The interference is so strong that it prevents the NIRQ signal from proper function. When I set the output power to the lowest setting I get a normal function. Can anyone suggest how to solve this problem? Or does anyone have a sample PCB layout that functions even with the highest output setting?

  31. @budlim

    I’ve not yet played around with the RFM12BP so am probably not much help.

    I can only suggest that if you are getting interference then look at more filtering and some form of shielding on the RF unit.

    sorry I can’t be more of a help. Stephen…

  32. hi,

    Now i am working with RFM12b,the problem is,c8051F120 controller can transmitted and c8051F326 can received properly,but
    while c8051F326 transmitting the c8051F120 is not receiving.for TX/RX, i am using RFM12b,,,,,,,,,,,,,,can u plz explain the problem ……………

  33. hi,

    Now i am working with RFM12b,the problem is,c8051F120 controller can transmitted and c8051F326 can received properly,but
    while c8051F326 transmitting the c8051F120 is not receiving.for TX/RX, i am using RFM12b,can u plz explain the problem ……………

  34. @volt

    How are you testing your Tx and Rx? as you say thet individually they both work?

    Really the problem you are describing can be anything.

    One of the common problems is incorrect bandwidth settings on the Rx. the Rx bandwidth settings must be greater than the Tx FSK settings? there are recommended settings in the datasheet from hope.

    Also check the frequency and bitrate setting so they are the same on both Tx and Rx.

  35. hi Stephen,

    Thank you for the response.
    In transmitting part i have c8051F326 controller.It always transmitting via RFM12b(3.3V).but the receiver side i am using c8051F120 controller to receive via RFM12b.
    the thing is i can able to TX/RX in F326.but when i using different controller to TX/RX,it cause the problem.F120 can able transmit but not able to receive.

    F120 F326
    fine
    (TX)——-> (RX)

    not RX
    (RX)<——- (TX)(no problem transmitting)

    i can forward to work with u r ideas and get back to you.

  36. hi,

    i am checking what u r suggest.The frequency and bit rate settings are the same on both TX and Rx.and also correct bandwidth settings on the Rx. It is greater than the Tx FSK settings.Is there any problem in nIRQ pin or SPI,HAL int..

    1. @volt

      I have found that I need to have a pull up on the NIRQ line for it to work, on the AVR I use the internal pullup for that pin. Also make use that you are reading the status as part of the IRQ handling i.e. cmd 0x0000 this resets the NIRQ on the RFM12, else it will stay low.

      Also don’t have any debug/printf to console in your main RFM12 Tx routines. The delay in Tx can cause the Rx to loose FSK sync.

      Stephen…

  37. Hi,

    do you have any idea how can I debug rfm12? Now, I have a transmitter, which send the data out in a loop and I have a receiver, which should receive the data, but it is only waiting in infinite loop and it doesn’t receive anything.
    What can i do in this situation? How can i check the rfm12 got my instruction via SPI? There is a status register in rfm, is it useful check the value of it?
    Thank you for your help!

    Regards,
    Gyorgy (from Hungary)

    1. @sogyu
      debugging the RFM12 can be frustrating, especially on the RFM12 side of things.

      to debug the SPI here is what I did:

      use an oscilliscope to check that the SPI signals looked ok, i.e. the NSEL is pulled low at the start of the SPI command and being returned high at the end of the SPI sequence. also check that the SCK signals looks ok and you have data going in/out from your MOSI/ MISO pins.

      If these look ok then try sending a command to change the frequency of the CLK pin. By default the Poweron value is 1MHZ (from memory) so put an oscilloscope or frequency counter on the output, then send the command to change to 10Mhz. if the SPI is working then you will see the frequency change to the new value.

  38. @Stephen

    Hi, I am trying to connect two PIC micro controllers using the RFM12B Transceivers and am having an issue with sending consistently. Each time I start up the transmitter and receiver sometimes I can start sending right away, and sometimes it takes a bit for the receiver to start catching the data that is being sent.

    Once NIRQ goes low the receiver will constantly receive data until I pause sending for a brief period of time. I have noticed that after I stop sending for a brief period, if I restart sending I begin to get all garbage values. I have also noticed that once NIRQ goes low it will not go back high even once I have stopped sending data. The data I am sending is 5 quick packets each consisting of a preamble, two sync bytes, 4 data bytes, then 3 dummy bytes. I have tried using the read status command to bring NIRQ back up after the 5 packets send but am still having an issue. Is there a way to reset the entire module or another way to pull NIRQ high using software? Any insight or tips would be greatly appreciated.

    -Thanks
    Matt

  39. @ernieb53

    I would try adding a some more pre-amble bytes as it sounds like a FSK lock issue, i.e. the receiver is not getting FSK lock then sync. I think a single pre-amble is not enough, and adding a preamble as the last couple of bytes in your packet, this allows your Tx register to flush out. I run at least 3-4 preamble bytes and tail my packets with 2 pre-amble bytes e.g. http://code.google.com/p/strobit/wiki/WidgetMesh#Design

    As for NIRQ, I’ve found you need a pull up for it to work properly, either an external resistor or easier still an internal one on your MCU port to pull the signal high. Remember when going into low power mode on your MCU you would need to disable the internal pull ups, before entering, and then re-enable when exiting sleep mode.

  40. @Stephen

    Thanks for the quick response and tips. As it turns out I am not using an interrupt but am just polling the NIRQ pin. I have tried the pull up resistor on both the micro and RF side along with the status read after each byte is read in, but I still never see NIRQ go high again. Could this be fixed if I enable interrupt instead of VDI for the p16 status bit? My preamble and dummy bytes are just how you suggested and the receiver does pick up more promptly. I even tried polling the FFIT instead of NIRQ and have found the same results of valid continuous data until I stop for a moment, then all garbage. If you have any other thoughts I would greatly appreciate any additional help. Thanks so much for the advice you’ve already given

    -Matt

    1. @ernieb53

      I always have P16 set to the POR values which is VDI, the INT is only for external interrupt for the RFM12, i.e. will stop the RFM12 from what its doing.

      The RFM12 interrupt system works by latching the interrupt source and then triggering the NIRQ line if any of these IRQ bits are latched (bits 0 – 5 of the status register), these bits are only cleared by doing a status cmd, so If the NIRQ line is permanently low and you are doing a status command as part of how you are handling the NIRQ state then you may need to read out the result of the status command to find the source of the RFM12 NIRQ is, you may find it’s low voltage or something else causing it, not the actual reception process.

      You might need to post or (email them to me via the contact form ) the commands being sent to the RFM12 as part of your initialisation sequence and then your Rx / Tx routines so I can see what’s happening,

      Also It’s important to remember that when initialising the RFM12 is to set the FIFO level to 8 bits (so when 8 bits get received/transmitted it will cause the FFIT interrupt to trigger) and also before you start any transmission/reception of your packet buffer you need to first disable (this resets the FIFO) and then enable the FIFO, then once everything has been transmitted/received you need to disable the FIFO.

      If you are only polling the NIRQ pin, then an easier way is to run the RFM12 in ‘polled mode’ basically this works during the reception (or Transmission process) by bit-banging a single 0 bit out the SPI and reading the single status bit back (FFIT), if the FFIT is 1 then do what ever, if 0 then do it again until a 1 is read back, (basically the same as doing a status CMD but only a single bit long) you don’t need to read the NIRQ line at all, keep in mind the MCU is tied up polling the RFM12, so not the most efficient.

      Basically sequence is:
      SCK = LOW
      NSEL = LOW
      SDI = LOW
      SCK = HIGH
      read SDO pin
      SCK = LOW
      NSEL = HIGH

      Stephen

  41. @Stephen

    Sorry about the delay, but once again thanks so much for your help. I did start using the FFIT read idea and it is working much better. I’m also going to include my code for transmitter, receiving, and initialization (receiver side).

    INIT

    writeCmd(0x80E7);
    writeCmd(0x8299);
    writeCmd(0xA640); //freq select
    writeCmd(0xC647); //4.8kbps
    writeCmd(0x94A0);
    writeCmd(0xC2AC); //AL,!ml,DIG,DQD4
    writeCmd(0xCA81);
    writeCmd(0xCED4); //SYNC=2DD4;
    writeCmd(0xC483);
    writeCmd(0x9850);
    writeCmd(0xCC17);
    writeCmd(0xE000);
    writeCmd(0xC800);
    writeCmd(0xC040); //1.66MHz,2.2V

    Transmit
    void rfSend(unsigned char data)
    {
    while(!NIRQ);
    writeCmd(0xB800 + data);
    }

    unsigned int writeCmd(unsigned int cmd)
    {
    unsigned char i;
    unsigned int recv;
    recv = 0;
    SCK = 0;
    CS = 0;
    for(i=0; i<16; i++)
    {
    if(cmd&0x8000)
    SDI = 1;
    else
    SDI = 0;
    SCK = 1;
    recv<<=1;
    if( SDO == 1 )
    {
    recv|=0x0001;
    }
    SCK = 0;
    cmd<<=1;
    }
    CS = 1;
    return recv;
    }

    short FFITcheck(void)
    {
    SCK = 1;
    CS = 0;
    if (SDO == 1)
    {
    SCK = 0;
    CS = 1;
    return 1;
    }
    else
    {
    SCK = 0;
    CS = 1;
    return 0;
    }
    }

    Receive
    unsigned char rfRecv()
    {
    unsigned int data;
    while(1)
    {
    data = writeCmd(0x0000);
    if ( (data&0x8000) )
    {
    data = writeCmd(0xB000);
    return (data&0x00FF);
    }
    }
    }

    void FIFOReset()
    {
    writeCmd(0xCA81);
    writeCmd(0xCA83);
    }

    That is most of my code for sending and receiving, and if you see anything that stands out as an obvious issue I would appreciate the help. Thanks so much for all the info so far!

    -Matt

  42. Hi Steve
    Great tutorial info. Just wondering if you can clarify some comments regarding nRST and FSK/DATA/nFFS. You mention that they should be tied high (directly and via 10k respectively) Reading the RF12B datasheet, nRST is a bidirectional pin with an internal pullup, and FSK/DATA/nFFS also has an internal pullup. I’m not worried about the couple of cents, but do they really need the external connections?
    Cheers
    Colin

  43. Hi Steve,

    Thanks for this tutorial, it was very handy in getting this radio module working.

    Just to point out that the RFM12B uses the Si4420 chip from Silicon Labs and is basically the Si4420 chip with the antenna circuitry shown in the Si4420 data sheet. This datsheet contains much more information than the Hoperf’s RF12B.pdf datasheet and actually explains for example how the transmission buffering works.

    From this you can see that it is not actually necessary to send preamble bytes. If the ET bit is off, the two stage transmission buffer pre-loads AA’s into this stage automatically. Once the ET bit gets set high these preamble bytes are sent as the first two bytes. If you want you can add more by pre-pending AAs to your data to tranmit. BTW you can override these two bytes if you write to the transmission register while ET is low (the datasheet shows this as a timing diagram).

    Mark.

  44. Proper Use of AFC:

    It seems to me that the AFC function is very useful to minimise the differece between the tranmitter and receiver frequencies, and hence to allow the minimum receiver bandwidth to be used.

    I’m a little unsure of exactly how the AFC function should be used though. Here is my basic understanding, maybe someone could shed some light on this and whether this is correct:

    When a receiver detects an incoming RF signal that is above it’s programmed VDI threshold the VDI signal goes active. This occurs during the preamble phase before any sync word. If the status word is read immediately VDI goes active (i.e. during the preamble stage), then the lower 3 bits show the frequency offset between the two frequencies, and this can then be programmed into the receiver frequency PLL register to match them. The sync word is then decoded with the receiver PLL now matched to the transmitter’s frequency, and subsequent data received (all further bytes received are not qualified with VDI, so the receiver will continue to receive even if the transmitter is turned off until either the receiver is disabled or the FIFO is reset).

    I’m also unsure about turnaround times between transmit to receive and back again. The datasheet gives a maximum time for these, but is this delay handled automatically by the hardware or does the micro have to add these times to allow it to settle? For example could the user immediately go into receive mode and the hardware prevent reception until the turnaround time has elapsed? Also could the user immediately try to transmit by setting ET after a reception and the hardware hold that transmission off until its internal turnaround time has elapsed?

    One last question: Does anyone know the ppm spec of the crystals used on the RFM12B? If AFC is not used this seems to be an important parameter when calculating the receiver bandwidth to be used.

    Thanks!

    Mark.

  45. I have seen a couple of comments about the RFM12B being based on the Si4420. It might be a minor point but from what I can see the RFM12B is actually based on the Si4421. My reason for thinking this is the 3.8V max supply, no support for 315MHz and flexible sync pattern (1 or 2 bytes) – this is what I have spotted so far. The fact that there are register differences between the Si4420 and RFM12B mean that it is not a good reference.
    Any comments welcome…

  46. i have tested the rfm12bp modules but the problem is with the range , it does not give good range . has anyone field tested it , i have the 915Mhz version . i don’t know if is a noise issue or something else. i have connected the module with a whip antenna . it should have enchanced range , hope rf says they have 800m range.

  47. @colinh

    Yes, I think you’re right. The RFM12 is based on the Si4420, the RFM12B is it seems is based on the Si4421 (the corresponding Hoperf documents for the chips are rf12.pdf and rf12b.pdf respectively). Thanks for pointing it out!

    Mark.

  48. @faizanbrohi

    Not sure what data rate you are using. There is a relationship between data rate and distance, basically for each doubling of the
    data rate the receiver sensitivity reduces by 3dB (roughly). Since power received reduces by 6dB for each doubling of distance this means the distance will reduce by 1/sqrt2, i.e. 0.707. Now you need to know what conditions the 800m is quoted for. You can bet this is at the lowest data rate the chip will handle, and at a releatively high Bit Error Rate (maybe 1E-3).

    Quick calculation: Assuming 800m is quoted at 600 bps, and you used 57600 bps in your app, this is (very roughly) 6 doublings, so your distance will reduce to 1/(6*sqrt2), i.e. again very roughly 1/10. You’ll get 80m, not 800m. And even that is at high BER rate.

    Here’s a useful link:
    http://www.ce-mag.com/archive/02/Spring/cutler2.html

    Mark.

  49. I am transmitting at 4800bps and it has reached 400m with only changing the board from Veroboard and a messy layout to a Well designed PCB one . i also changed the antenna. i am now looking forward to the 433Mhz module to increase the range as it low frequency so greater wavelength . will the low frequency module make a difference ?

  50. Dear All,

    Please help me out with this issue:
    I am reading the status register but getting only 0’s
    This is the init function:
    void RF12_INIT(void) //868MHz!!!
    {
    RFXX_WRT_CMD(0x80E7);//el,ef,868band,12.0pF

    //If both et and er bits are set the chip goes to receive mode.
    RFXX_WRT_CMD(0x8259);//!er,ebb,!et,es,ex,!eb,!ew,DC

    RFXX_WRT_CMD(0xA640);//868MHz
    RFXX_WRT_CMD(0xC647);//4.8kbps
    RFXX_WRT_CMD(0x90C0);//VDI,FAST,67kHz,0dBm,-103dBm
    RFXX_WRT_CMD(0xC2AF);//AL,!ml,DIG,DQD7
    RFXX_WRT_CMD(0xCA81);//FIFO8,SYNC,!ff,DR
    RFXX_WRT_CMD(0xCED4);//SYNC=2DD4
    RFXX_WRT_CMD(0xC483);//@PWR,NO RSTRIC,!st,!fi,OE,EN ??
    RFXX_WRT_CMD(0x9830);//!mp,45kHz,MAX OUT
    RFXX_WRT_CMD(0xCC77);//OB1COB0, LPX,!ddy,DDIT,BW0
    RFXX_WRT_CMD(0xE000);//NOT USE
    RFXX_WRT_CMD(0xC800);//NOT USE
    RFXX_WRT_CMD(0xC000);//1MHz,2.2V

    }//void RF12_INIT(void)
    the write command function:
    unsigned int RFXX_WRT_CMD(unsigned int aCmd)
    {
    unsigned char i;
    unsigned int temp=0;

    _delay_us(10);

    LOW_SCK();
    LOW_SEL();

    _delay_us(10);

    for(i=0;i<16;i++)
    {
    if(aCmd&0x8000)
    HI_SDI();
    else
    LOW_SDI();

    aCmd<<=1;

    _delay_us(40);
    HI_SCK();
    _delay_us(20);

    if(SDO_HI())
    temp|=0x0001;

    temp<<=1;

    _delay_us(20);

    LOW_SCK();
    }//for(i=0;i>8);
    USART_TransmitByte(tmp&0xFF);

    RFXX_WRT_CMD(0xB800+aByte);
    }//void RF12_SEND(unsigned char aByte)

    And a part of main():
    …. RFXX_WRT_CMD(0x8279);//!er,ebb,et,es,ex,!eb,!ew,DC

    //RFXX_WRT_CMD(0xCA81); //init fifo
    //RFXX_WRT_CMD(0xCA83); //enable fifo
    //RFXX_WRT_CMD(0x0000);//read status

    //_delay_ms(5);

    ChkSum=0;

    LEDR_ON();

    RF12_SEND(0xAA);//PREAMBLE

  51. Dear All,

    Please help me out with this issue:
    I am reading the status register but getting only 0’s
    This is the init function:
    void RF12_INIT(void) //868MHz!!!
    {
    RFXX_WRT_CMD(0x80E7);//el,ef,868band,12.0pF

    //If both et and er bits are set the chip goes to receive mode.
    RFXX_WRT_CMD(0x8259);//!er,ebb,!et,es,ex,!eb,!ew,DC

    RFXX_WRT_CMD(0xA640);//868MHz
    RFXX_WRT_CMD(0xC647);//4.8kbps
    RFXX_WRT_CMD(0x90C0);//VDI,FAST,67kHz,0dBm,-103dBm
    RFXX_WRT_CMD(0xC2AF);//AL,!ml,DIG,DQD7
    RFXX_WRT_CMD(0xCA81);//FIFO8,SYNC,!ff,DR
    RFXX_WRT_CMD(0xCED4);//SYNC=2DD4
    RFXX_WRT_CMD(0xC483);//@PWR,NO RSTRIC,!st,!fi,OE,EN ??
    RFXX_WRT_CMD(0x9830);//!mp,45kHz,MAX OUT
    RFXX_WRT_CMD(0xCC77);//OB1COB0, LPX,!ddy,DDIT,BW0
    RFXX_WRT_CMD(0xE000);//NOT USE
    RFXX_WRT_CMD(0xC800);//NOT USE
    RFXX_WRT_CMD(0xC000);//1MHz,2.2V

    }//void RF12_INIT(void)
    the write command function:
    unsigned int RFXX_WRT_CMD(unsigned int aCmd)
    {
    unsigned char i;
    unsigned int temp=0;

    _delay_us(10);

    LOW_SCK();
    LOW_SEL();

    _delay_us(10);

    for(i=0;i<16;i++)
    {
    if(aCmd&0x8000)
    HI_SDI();
    else
    LOW_SDI();

    aCmd<<=1;

    _delay_us(40);
    HI_SCK();
    _delay_us(20);

    if(SDO_HI())
    temp|=0x0001;

    temp<<=1;

    _delay_us(20);

    LOW_SCK();
    }//for(i=0;i<16;i++)

    LOW_SCK();
    HI_SEL();

    return temp;

    }//unsigned int RFXX_WRT_CMD(.. aCmd)

  52. The previous message got scrambled..
    Here is again in two parts
    Write command:
    unsigned int RFXX_WRT_CMD(unsigned int aCmd)
    {
    unsigned char i;
    unsigned int temp=0;

    _delay_us(10);

    LOW_SCK();
    LOW_SEL();

    _delay_us(10);

    for(i=0;i<16;i++)
    {
    if(aCmd&0x8000)
    HI_SDI();
    else
    LOW_SDI();

    aCmd<<=1;

    _delay_us(40);
    HI_SCK();
    _delay_us(20);

    if(SDO_HI())
    temp|=0x0001;

    temp<<=1;

    _delay_us(20);

    LOW_SCK();
    }//for(i=0;i>8);
    USART_TransmitByte(tmp&0xFF);

    RFXX_WRT_CMD(0xB800+aByte);
    }//void RF12_SEND(unsigned char aByte)

  53. I solved the problem, now my concern is that switching between tx/rx takes to long.
    As trying to implement some anti-collision I need to stop tx for a while and check for any rx. Anybody has some ideas ?

    When finished I will make the code public.

  54. @laci

    Great to hear you have it working.

    If you leave the crystal and synthesiser on then the turnaround time from Tx – Rx and visa-versa is 150usec. Initial crystal turn-on time is a couple of mSec so do that at initialisation toggle the et bit.

    You can also the ATS, DQD and RSSI status bits to determine if there is something else transmitting.

    Stephen…

  55. Hello , again , there is some problem with the module when i am using interrupt mode , i am using the following scenario ,

    There is one Gateway ,router, base station or what ever you want or call it , which polls different nodes which are listening. the base station broadcasts an address packet to every node and the corresponding node answers if it matches the address . i have three nodes currently connected to the system .

    Now the problem is that after some time the base station (when it is polling) receives zeroes at the end of every packet and it is consistent. when i introduced a watchdog and when it resets the system the zeroes are gone , but this does not solve the problem it can occur everytime , is it a timing issue , i am using my own interrupt based routine and check nirq for it to go in the external interrupt ISR and the ffit bit for receiving the valid data.

    i have 1 second polling time for each node @ 4800kbps ( which is done under timer ISR ) and about 10 ms switch over time for tx-rx switching , it has enough time.

    I mailed hoperf , they are saying add 10k pullup to the fsk data pin . however it did not solve the problem .

  56. @faizanbrohi

    With your interrupt routing are you checking or handling all status bits? as the interrupt might be generated by something else.

    It’s not safe to assume that when you receive an interrupt that it is from a Tx or Rx event.

    Regards,

    Stephen…

  57. @stephen

    Solved the problem , problem with node synchronization when handling two interrupts (timer and external), a programming bug not the rf issue. Thanks

  58. hi stephen, I just started to work with the RFM12b and the pic 16F87. is the first time I do program a device, so I would like to know wich compiler could i use.

  59. hi stephen, I just started to work with the RFM12b and the pic 16F873a. is the first time I do program a device, so I would like to know wich compiler could i use.

  60. @Stephen

    I “reloaded” the rfm project, and still struggling with the rx/tx mode switch.
    Before I issue the actual command
    RFXX_WriteCommand(0x8279);//!er,ebb,et,es,ex,!eb,!ew,DC
    or
    RFXX_WriteCommand(0x82D9);//er,ebb,!et,es,ex,!eb,!ew,DC

    I wait for the Status bit FFIT to be 1.
    The problem is that the device switches to RX mode very slow, do you have any idea why?

    Regards,
    Laci

  61. hi all, i use rfm12b to transmit data from a PC to another one by rs232. most of my code from hope rf.
    PC1–(1)–>MCU1–(2)–>RF1—(3)—>RF2–(2)–>MCU2–(1)–>PC2
    but i’m puzzling with the bitrate among these devices.
    as u see on the simple diagram above.
    (1) : bitrate between PC and MCU
    (2) : bitrate between MCU and RF
    (3) : bitrate between RF and RF

    acorrding hope code,
    writeCmd(0xC647); //4.8kbps
    data rate (3) is 4800bps.

    is it necessary to be the same among them?

    hearing from you soon!

  62. @Stephen,

    Well it takes quite long(few 100ms), usually the first attempt gives a timeout, and sometimes can’t even switch between tx/rx.

  63. @ Stephen 89

    I’ve set up a system using two rfm12 to transfer data from one node to another but it’s still not worked at all. I also used a electromagnetic energy device to detect the magnetic field but maybe that device was not sensitive enogh!!!
    Would you mind telling me how to check if rf really sent out a frame?

    may a oscilloscope can kick this problem?

    thanks a lot!

  64. @laci,

    100mSec would seem long as a turn around time.

    make sure you’re not tuning off the whole power chain when you change from Tx-Rx and vis-versa. If you want a fast turn-around then you need to already have the crystal oscillator and synthesiser turned on (part of your wakeup?).

    Once initialised you should only need to toggle the er bit in the power control register(0x8208h) if both et and er are on then er takes precedence.

    check out the turnaround timing in the datasheet (bottom page 10 on my sheet), in theory you should be achieving 150uSec turnaround times if you already have the synthesiser and crystal on.

    Stephen…

  65. @realheaven

    AFAIK a spectrum analysers would be the only thing to see if you are transmitting on the wireless side of things. An oscilloscope would cause too much load on the circuit and then it won’t work, also the frequencies involved would be a high end oscilliscope.

    You need to confirm your SPI is talking to the RFM12 first. An easy test is to send the comand to change the Cystal output frequency and measure with an oscilloscope or frequency counter.

    If your having Tx Rx problems make sure you don’t have any debug printf etc in your transmit routines, just queue up your Tx buffer and then start the Tx sequence until your buffer is empty.

    If there are any delays in this Tx sequence then the receiver will loose sync and will not receive anything.

    Stephen…

  66. @Stephen,

    I am changing just the et/er bits in the power managment command

    this is my function:
    unsigned char RF12_SetMode(unsigned char SetMode)
    {
    static unsigned char timeout_cnt=0;
    unsigned char RFXX_Response;

    RFXX_Response=RFXX_WaitReady();

    if( (SetMode==TX_MODE)&&(mode==RX_MODE) )
    {
    //Fill the TX with 0xAAAA preamble key
    RFXX_WriteCommand(0x8279);//!er,ebb,et,es,ex,!eb,!ew,DC
    _delay_ms(1); //RX/TX switch time
    mode = TX_MODE; //switch to tx mode
    RFXX_WriteCommand(0xCA81); //reset fifo
    }
    else
    if( (SetMode==RX_MODE)&&(mode==TX_MODE) )
    {
    RFXX_WriteCommand(0x82D9);//er,ebb,!et,es,ex,!eb,!ew,DC
    _delay_ms(1); //RX/TX switch time
    mode = RX_MODE; //switch to rx mode
    RFXX_WriteCommand(0xCA81); //reset fifo
    }

    if(timeout_cnt == RFXX_SET_MODE_TIMEOUT) //prevent infinit blocking
    {
    RFXX_Response=RFXX_READY;
    timeout_cnt=0;
    }

    if(RFXX_Response != RFXX_READY)
    {
    timeout_cnt++;
    return RFXX_TIMEOUT_ERR;
    }
    else
    return mode;
    }//unsigned char RF12_SetMode(unsigned char SetMode)

  67. @ Stephen 93

    thanks so much for your support. I checked my SPI interace and there was no trouble with it.
    I gotta read the status register to comfirm that i can manage the rf completely.
    There is a simple code to read the status register is :
    writeCmd(0x0000) // form hope guide

    but i failed in this section

    is that enogh to read status register by a sigle command like that?

  68. here’s my complete code

    // rs232 Init
    void Tx(unsigned char data)
    {
    while(!(UCSRA & (1<<UDRE)));
    UDR=data;
    }
    // write command function
    unsigned int writeCmd(unsigned int cmd) {
    unsigned char i;
    unsigned int recv;
    recv = 0;
    LO(SCK);
    LO(CS);
    for(i=0; i<16; i++) {
    if(cmd&0x8000) HI(SDI); else LO(SDI);
    HI(SCK);
    recv<<=1;
    if( PINB&(1<<SDO) ) {
    recv|=0x0001;
    }
    LO(SCK);
    cmd<<=1;
    }
    HI(CS);
    return recv;
    }

    to be continued…

  69. void rfInit() {
    writeCmd(0x80F8); //EL,EF,915band,12.5pF
    writeCmd(0x8239); //!er,!ebb,ET,ES,EX,!eb,!ew,DC
    writeCmd(0xAA6B); //frequency select
    writeCmd(0xC647); //bit rate = 4.8kbps
    writeCmd(0x94C2); //VDI,FAST,BW=67kHz,0dBm,-91dBm
    writeCmd(0xC2AC); //AL,!ml,DIG,DQD4
    writeCmd(0xCA81); //FIFO8,SYNC,!ff,DR
    writeCmd(0xCED4); //SYNC=2DD4G
    writeCmd(0xC483); //@PWR,NO RSTRIC,!st,!fi,OE,EN
    writeCmd(0x9820); //!mp,deviation=45kHz,MAX OUT
    // writeCmd(0xCC17); //OB1COB0, LPX,IddyCDDITCBW0
    writeCmd(0xE000); //NOT USE
    writeCmd(0xC800); //NOT USE
    writeCmd(0xC040); //1.66MHz,2.2V
    }

    void main()
    {
    volatile unsigned int data;
    #asm(“cli”);
    delay_ms(1000);
    rsInt();
    portInit();
    rfInit();

    data=writeCmd(0x0000);
    Tx(data);
    }
    status register value form hyperterminal : 00 00 00 00…
    please help me in this case

  70. what funny!
    when rf in Tx mode, i got a static valaue form status register is A100. but when i toggled it into Rx mode i got more than one value!?! for ex : 0000, 0120, 0020 and several strange values : 0040, 0044, 0067!?!

    i note that there are two bits in status register having value changing are RSSI and ATGT.

    anybody can explain why in Rx mode there are lots of diffrent values when reading status register? expecially bit RSSI & ATGT

  71. at least my network works! i feel so happy! it’s worth to try hard rite! 😉
    but who can tell me why toggling between TX/RX & RX/TX take so so long time. I must to delay 500ms to guagrante receiving all packets whereas hoperf say that it takes 150us!?!
    thanks a lot!

  72. @realheaven

    Glad you got it all working, what ended up being your problem?

    One of the other members (laci) is also having problems with the turnaround time from Tx/RX as well, you might want to chat with him to see if a solution was found. Unfortunately I not currently in the position to do any testing for some time so I see why there is a delay.

  73. I hope somebody can help me out, I ran out of ideas, probably will switch to some other module/solution because this rf12b just won’t work …

  74. @realheaven

    The TX/RX switching won’t work, at start up I can switch to TX(no received data yet), it sends out the data, after I start to receive the RX mode won’t gather any data, and I can’t switch back to TX mode.

    See my previous posts, I even posted the mode select function.

  75. @ laci 106

    at first, if you want one node at TX mode then you should init it @ TX mode by writeCmd(0x8239). Next, if you want it at RX mode you should switch it to RX mode by writeCmd(0x8299).
    You can also test the TX RX mode with one simple test. For example, you have 2 node A & B.
    1. A (TX) —> B(RX)
    2. A(TX–>RX) & B(RX–>TX)
    3. B(TX)–>A(RX)

    A sends out a byte to B, A immediately switches to RX mode; if B (@ RX)receives a byte and check if it’s from A then B switches to TX mode and sends out a byte; @ A you can easily check the data from B by send it to PC using RS232.

    ps : you should test both two nodes that can transmit and receive data first to be sure that there’s no fault at any stage of the process.

    good luck!

    (feel free asking, rite!) 😉

  76. I will make a more thorough debug, maybe I made some stupid mistake somewhere… until then I remain skeptic 🙂 just won’t switch between tx/rx remains blocked somewhere 🙂

  77. As soon as I have some spare time, i will get to the bottom of this issue :), and write my own tutorial and post my entire software on a blog.

  78. Hello Stephen,
    Really thanks for these nice tutorials!!!
    i thought i gave up on that rfm12!!! i used the hm-tr from hope rf wich uses standrd rs232 protocol but they are very expensive !!! my question is if i want to use the hardware spi will the code be the same as the programming guide??

    Note: I am Using Mikroc And has an spi library (hardware)(Pic16f876a)

    Thanks Alot Stephen .

  79. @Nart_schinakow

    I would suggest you look at other examples of code other than the ones supplied from HopeRF. I had no end of problems with them. However in saying that I did have some problems getting the hardware SPI working with the PIC and the RFM12B, this was a couple of years ago though.

  80. Hi,
    I am trying to interface a at89c52(5V) with the RFM12B(~3.6V) module. Whether I need to take care about including any delimiting resistors or other kind of level shifters between the SPI bus pins.
    thanks in advance
    Geo

    1. @geo

      The RFM12B has 5V tolerant I/O, however in saying that I wouldn’t leave it running at 5V for an application as it may shorten it’s life. When I first started development I didn’t use shifters etc and all ran ok.

  81. @ geo 116

    you may choose RFM12 instead of RFM12B because RFM12 can run well at 5V so there’s only one power supply for the two devices and to manipulate those RF is the same.

  82. Hi Stephen
    I have been researching and developting an application using the RFM12B.The data on this module is not good,
    What i have noticed is a Digital signal analyzer or scope is required becasue of the lacking data sheets as to correct program flow.
    What would be a good start is if an experience rfm developer(yourself) could provide timing diagrams showing the state of lines
    NSEL,SCK,SDI,SDO,nIRQ, and VDI in relationship to el,et,synthersizer/pa etc,etc when running a sample program.
    Now i am using a scope things are becoming much easier to grasp
    Chippchipp

  83. @chippchipp

    Yes I can certainly appreciate what rfm12 newbies go through. the biggest problems is what comes first the chicken or the egg, e.g. is the problem in the Tx, or is it in the Rx side of things.

    I certainly agree with you. I could not have got my original design working without an oscilloscope watching the CLK and the MOSI/MISO however this was a pain as I only have a two channel CRO, I’ve since treated myself to a logic analyser that can decode SPI and find this invaluable when I troubleshoot.

    When I get around to finishing off the tutorials I’ll look at putting some timing diagrams on.

    stephen…

  84. hi,
    The last time I contacted you was Dec 2010.
    Now have my project working fully and I think I understand about 55% of the workings of the RFM12b.
    The two modules communicate 100% no problems.
    One thing I have notice.
    I replaced my original Rfm 12b modules with two new rfm12b which I purchased in july 2011.
    After power up i found problems with the first second and maybe third communication data packet occurs now and then but after say the fourth data packet the two modules will communicate continuously, not missing any data thereafter until I power off and power up or I move one of the modules out and then back in range.
    I reverse fitted the new modules (swapped them round on my embedded application) and guess what.
    I modules communicated perfectly from power up??
    Have you seen this or have any ideas to what to change to debug or tune this out.
    The two modules are embedded on exactly the same pcbs..
    Just one module acts as the master and the other the slave.
    I have increased the preambles.No change
    Are there any parameters which you could point me to look at

    Thanks
    Chippchipp

  85. hello friends
    plz help me
    i worked on rfm12b for 1 month i have a problem that make me crazy
    when i turn it on everything is good and a read status with 4000 hex
    but when i initialize the module and switch to tx mode from ideal
    the status run to a100 hex
    i cannot solve the issue
    plz help me i beg u friends

  86. Hi, i’m a debutante in Arduino and RFM communications.

    I’m trying to develop a project in which a led turns on according to the distance that is between an transmitter and a reciever.
    I’ve followed all your connecting instructions, followed the “Simple RFM12B demos” and connected the “pin15” by welding the ARSSI.
    Now I recieve only “0” and there is no way to change it. I’ve change the jeelib as CapnBry from the jeelabs.net said in “Homemade BMP085 Node in a Garden Light” (http://forum.jeelabs.net/comment/6203.html) to amplify the reading of the signal but there’s no good result.

    Does someone has a simple “hello world” ARSSI demo or some further instructions to achieve the reception of different values acording to the distance?

    I hope someone can help me.
    Thank you,

    Canto

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