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31  Community / Exhibition / Gallery / Re: Cheap UHF spectrum analyzer using RFM22 module on: July 01, 2012, 08:44:27 am
Hi guys,

Since I have sold and/or used all of my boards, I decided to make a batch of new ones.

The major updates of the Rev 3 boards will be:

- Smaller: 37x48mm, vs. 43x50mm Rev 2
- Will use a slightly better LDO for 3.3V: MCP1825S. With only 210 mV drop out, so may benefit people like myself that using lots of servos powered from 5V.
- 0.1 inch pin spacing for servos!!!!111

See attached pictures.

I will be making a new batch of 10 boards, mostly for my own use. If you want any please let me know. Also if you have any suggestions/comments I will be interested to hear. I have a choice of different board colours and thicknesses too...
32  Community / Exhibition / Gallery / Re: Cheap UHF spectrum analyzer using RFM22 module on: June 24, 2012, 08:02:47 pm
It could be quite nice to have the boards act as a wireless serial bridge. Telemetry boards with similar performance are usually much more expensive.

Please share your code when you get it working!
33  Community / Exhibition / Gallery / Re: Cheap UHF spectrum analyzer using RFM22 module on: June 07, 2012, 11:13:45 am
Looks great! Glad you got it working!

Good point on the pin spacing. I found that it was quite annoying trying to solder 10 3x1 pins as well.

You only need the switch if you plan to use my RC transmitter code, in which the switch changes output power. If you do use a switch like the one I used, make sure the metal parts of don't short out the pins under/around it like I did!

34  Community / Exhibition / Gallery / Re: Cheap UHF spectrum analyzer using RFM22 module on: June 02, 2012, 04:08:53 pm
It's register 05 for the RSSI.

Btw, after almost a month I got an email saying that my RFM22 were shipped...
I had asked to include one of these cheap 2.4Ghz... but got no reply. :S

We'll I'm going to start assembling the boards as yesterday I got the solder paste and I expect the RFM's to arrive during next week.

That's a long time to wait! I have been flying my plane with the RFM22, it's working great so far.

Register 05 is write-only,  it's "RSSI Threshold for CD detect". You can't read the RSSI value from it.
35  Community / Exhibition / Gallery / Re: Cheap UHF spectrum analyzer using RFM22 module on: May 23, 2012, 06:22:05 pm
As I got the order stuck there, I was wondering about this:
If I can build the same frequency scanner with it as well for 2.4Ghz. From the specs it seems so as the frequency can be selected up to
a 1Mhz interval.

That is pretty cheap, but I don't see a register for the RSSI value anywhere.
36  Community / Exhibition / Gallery / Re: Cheap UHF spectrum analyzer using RFM22 module on: April 29, 2012, 10:07:37 am
Here is the code for a standard 10 channel PPM RC tx+rx for my boards. You must use my modified version of the RF22 library!

On the TX you need to connect 5V PPM to header D3. You can put a switch or jumper on the header next to the RF22 (GPIO2) to switch between low power (1dBm, 1.3mW) and high power (20dBm, 100mW, red LED on). You can easily change the frequency in the code (remember to change rx as well!).

On the RX the LEDs indicate RSSI values: Green > -70dBm, Green+Red > -85dBm, Red > -100dBm, else/no signal = no LED.

Be careful not to connect servos the wrong way around. I didn't use current limiting resistors on the arduino pins to save having to solder 10 more SMD resistors, so it is possible to damage the output pins if they somehow get stuck on and end up powering your servo!

37  Community / Exhibition / Gallery / Re: Cheap UHF spectrum analyzer using RFM22 module on: April 29, 2012, 09:49:34 am
Hi Z,

I'm gathering together some bits as the data is apparantly sent over 433.92MHz AM radio by OOK (On-Off-Keying) and there is some info on the 'tinterweb about the protocols used.

I may just get another weather station with serial out on the receiving consol and do it that way.

I also have a Raspberry Pi on order (for ages now), maybe a low power web server and automatic weather station??!!

Too many projects and not enough time...!


The RF22 can certainly do OOK, but it will not be trivial to do the software to read whatever protocol they use... Maybe it's possible to intercept the data before it gets to the transmitter on the weather station, and use your own tx rx? I also want a Raspberry!

In regards to the RFM22B I've talked to someone that is trying to get some as well and the only ones he could find
 available were the RFM22B-868-D, will those work?
Does it need to be the 433 model or it's possible to change the frequency.

The 868MHz version should work just fine. I can even change my 434 module to 960MHz, but obviously it won't work very well. You might need to make sure that 868MHz is a legal frequency in Ireland!

Okay  one thing iv noticed between the different in graph that you postted and the one i posted yours seems to be a lot cleaner and not as jagged spiked like mine . but that said mine is set to max output.

once i get my board from you i would like to use it to test home made 433 radios . what would be the best set of settings for use with RF probes and not antennas? i would image i would set the Tx/Rx power right down to minimum ?

Did you leave it alone to gather data for long enough? The peak value should smooth out over time.

I think the best way to test radio output would be to connect the tx to rx directly with an attenuator, so you don't have to worry about antenna weirdness. Then again, I am definitely not qualified to answer any RF related questions!
38  Community / Exhibition / Gallery / Re: Cheap UHF spectrum analyzer using RFM22 module on: April 28, 2012, 01:25:43 pm
Hi zitron,

Where did you get your RFM22B? The only that I can find seem to have the emitting power locked and can't do the 100mW.


I know about Flytron gear I actually bought some other parts from them, but yes my intention is to get bare PCB's.
I have all the remaining parts just the PCB that is missing.

I got some time ago some similar RFM boards (RFM21 I believe) to do a telemetry project but got sidetracked and ended
going for BlueTooth and developing an app for it. And the the boards are still here getting dust.

But what you share here is on a another level  (special in what concerns range) and rather interests me, so I eager to try it
 and put my hands on the code as well. smiley

Oh, does that mean you can help with the code?? I have 4 boards left, Rustie0125 wants 1, so you can have the last 3. PM me your address, email and how many you want.

My first board works just fine as a spec analyser.
I've yet to build my other boards.

I'm a bit like you, no big motivation for UHF at the moment (I have OpenLRS for UHF R/C), plus I have a couple other projects - including weather monitoring, maybe with an RFM22B and an Arduino smiley-wink

Cool. I can help you with the code if your weather telemetry project is something simple, like tx/rx of serial data or something.
39  Community / Exhibition / Gallery / Re: Cheap UHF spectrum analyzer using RFM22 module on: April 26, 2012, 04:25:08 am
thanx for confirming that . so for example if the RF22 radio max output is 17-20dBs then if i transmit next the the analyzer i will see a 20 dB jump in the graph but so if it was -120 it will  be -100 or around there.

You will only see a 20dB jump if you were perviously transmitting at 0dB! Theoretically, if you are transmitting at 0dBm (1mW), and connect the tx directly to the rx with a coax cable (do not do this!) you will see 0dBm on the receiver. However in real life and if you are using antennas, you will see the rx RSSI change from about -20 (the RF22 will not report RSSI higher than -20) to -100 as you move the rx away from the tx.

regarding the Antenna issue , all i really wanna test with these unit is if RF equipments is working or not. for example if i have a 433mhz remote i just want to Tx next to it and see a jump in the graph so Accuracy is not that big of a problem. what i think i would do is make a small Antenna relay board with antenna's made for 900mhz, 433mhz and 600mhz and when i switch between them the reply will latch to the correct antenna Automatically i know its not the best but i think it will be best this setup can do.

are you planning on upgrading the Pc app with more functions ?

like to see if you can set a start line on the average incoming signal and the app will update the max output line at the top of the graph and under the setting just show a tab that updates the dB difference between the two lines.

That will probably work ok, but you will need to write your own code. I might add more to the PC program, but it's not really a priority. You can do your own data processing by collecting the serial data and plotting them in MS Excel or MatLab or even do it on the arduino chip.

This is and excellent project! smiley
I really want to try it out in my FPV quads.

Does anyone has PCB's to sell?
Unfortunately I have no way to make them.
(well I could but I'd probably ended up sleeping in the balcony)


Basically what Devonian said. If you want one or two boards that work right out of the box, you are better off getting the openlrs. I only have the bare pcbs.

BTW, Nigel did you get the thing working on your main PC? If your boards are working properly I'll put together some RC PPM code this weekend for you to test. I've not really been motivated to do much this past week because of the terrible weather!
40  Community / Exhibition / Gallery / Re: Cheap UHF spectrum analyzer using RFM22 module on: April 21, 2012, 10:38:55 am
Hi Z,

I'm also using 0023.

I made a clean install on netbook and copied your RF22 library (from your post above) into the clean libraries folder.
Copied the code (from above) and made a new pde called 'rf22_specan_simple' and veried it.
It compiled OK.

Ran up your RF22SpecScan.exe and it runs fine.

I'll try some more later on my main PC and Laptop as this is where I want to mostly use it.


OK that's good.

if you look at the picture with only the RF22 switched on that is working as the receiver it would appear that there is a very high signal detected in the UHF range where i stay ? or am I seing it wrong ?

also the labeling of the dBs on the left hand side would it not make more sence if it started form -120 at the top and -20 at the bottom? I arleady made the mistake at looking at the spike but in reality if i understand it correct is actually the lowest detected frequency that im looking at , can it be swapped ?

That looks pretty normal.  The RF22 is not meant to be a spectrum analyzer, it will only work properly for the frequency range the module and antenna is made for. You can force it to whatever frequency you want, but results will not be accurate.

RSSI is a logarithmic scale, you are reading it wrong. See

I just remembered that that I have made some small improvements to the PC program, I have attached the new version.
41  Community / Exhibition / Gallery / Re: Cheap UHF spectrum analyzer using RFM22 module on: April 21, 2012, 09:17:22 am

I loaded both versions now and they seem to work great . thanx , one question , they PC application seem to very slow updating the graph

Update speed depends on how many steps you are scanning. By default it scans from 430-460MHz at 0.1MHz step (300 samples), which is a bit slow. You can make it faster by increasing the step size or reducing frequency range.

BTW are you using your own board??
42  Community / Exhibition / Gallery / Re: Cheap UHF spectrum analyzer using RFM22 module on: April 21, 2012, 07:55:05 am

I knew there would be problems!

Which version of arduino are you using? I'm using 0023, I have not tested it on version 1.0.

Try this version of the specscan without the fastserial stuff:

// rf22_specan
// A simple spectrum analyser for the RF22
// Uses the RSSI measurement to plot signal strength
// against frequency
// Specify the start and and requencies and the step size below.
// The output is suitable for a VT100 terminal emulator
// Note the baud rate is set to 115200 for better performance,
// but you can change this to suit your needs
// TO DO: add some interactivity
// Copyright Mike McCauley

// modified to work with PC program
// Zitron

#include <RF22.h>
#include <SPI.h>

#define redLED 18
#define greenLED 19

char temp[51];
uint8_t rssi;
// Singleton instance of the radio
RF22 rf22;

void setup()
  pinMode(redLED, OUTPUT);
  pinMode(greenLED, OUTPUT);
  if (!rf22.init())
    Serial.println("RF22 init failed");

  // Defaults after init are 434.0MHz, modulation GFSK_Rb2_4Fd36
  digitalWrite(greenLED, HIGH);

float Start = 430;
float End = 460;
float Step = 0.1;

float freq;

void loop()
  for (freq = Start; freq < End; freq += Step)
    digitalWrite(redLED, LOW);
    delayMicroseconds(6000); // Let the freq settle
    digitalWrite(redLED, HIGH);
    rssi = rf22.rssiRead();
    Serial.print(rssi, DEC);

void ProcessRx() {
  byte n = 0;
  byte m = 0;
  char* sptr1;
  char* tempstr;

  if (Serial.available()) {
    temp[n] =;
    while ((temp[n] != '\n')&&(n<50)) {
      if (Serial.available()) {
        temp[n] =;


    tempstr = strtok_r(temp,",\n",&sptr1);

      switch (m) {
      case 0:  // Wheel 1
        Start = atof(tempstr);
      case 1:  // Wheel 2
        End = atof(tempstr);
      case 2:  // Wheel 3
        Step = atof(tempstr);
    while (tempstr = strtok_r(NULL, ",\n",&sptr1));

I have also uploaded my modified version of the RF22 lib.
43  Community / Exhibition / Gallery / Re: Cheap UHF spectrum analyzer using RFM22 module on: April 18, 2012, 12:13:23 pm
Hi guys,

For those of you building the board, here's a test code to make sure that the ATMEGA is working. It simply blinks the red and green LEDs:

#define OUTA 18
#define OUTB 19

unsigned int duration = 500;

void setup()
  pinMode(OUTA, OUTPUT);
  pinMode(OUTB, OUTPUT);

void loop()

44  Community / Exhibition / Gallery / Re: Cheap UHF spectrum analyzer using RFM22 module on: April 16, 2012, 10:25:52 am
Today I received the Zitron PCB's, look much better in my hands than here in the pictures !   smiley-grin
Now just need to buy the RFM22.

Cool! Let me know how it goes!

What differences are between RFM22-S1 and RFM22-S2? Only the crystal size?

I heard someone mention that the bigger crystals have better frequency tolerances, but that could be just a rumour.
45  Community / Exhibition / Gallery / Re: Cheap UHF spectrum analyzer using RFM22 module on: April 14, 2012, 06:34:58 am
Thanks! you gave a very clear answer smiley-grin...Why does flytrons TX module have 2 vregs, mic5205 and a LM2937?

They use 2 at the same time?? I really donno, will have to look at their schematics...

What you think about a integration of the RFM12BP with your circuit in the future? Seems to be very similar to rfm22 but with 500mw. It is possible without modifications on your code?

No the RFM12BP (and lower power RFM12) uses a completely different RF chip. Although there are probably arduino code for it somewhere on the intarwebs since it's been around for a while.
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