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Topic: Cheap UHF spectrum analyzer (and RC tx rx) using RFM22 module (Read 107230 times) previous topic - next topic


I couldn't tell from your video, but make sure you also check the hardware power selector/switch next to the RF22. You shouldn't need to change the software if you just add a jumper.

For power I just soldered a wire from the 5V reg on my 9X.


Dec 01, 2012, 04:37 pm Last Edit: Dec 01, 2012, 04:40 pm by Nandox7 Reason: 1
I've disabled the jumper check code, so it's always using the same power.
What I had forgotten to do was check the initialization settings on the TX.

As for the power regulator I recalled I had here a tiny pcb with a voltage reg from a old Wireless camera kit.

Couldn't be better, it converts from 12v to 5v and has place to solder two more wires that I'm using for the PPM and Serial TX.
It's a 78L05 so It's pushing it a bit, but I let it on for quite some time and it didn't burnt.


How does one change the frequency easily on this? I'm looking at http://www.futurlec.com/Radio-433MHZ.shtml (and also the one from Sparkfun) and they all seem to indicate that the parts on the board constrict it to specific frequency and it wouldn't work on others, yet you guys seem to be able to switch along the entire range with no problem.


You can change normally using the registers. It can work all over the full range allowed by the SIL chip.
What happens is that hoperf adds some filters that will make it work better on model range. So don't expect to have the same
performance on 866Mhz if you're using a model for 433Mhz.
Example, for the purpose of acting as a frequency scanner is it ok for a LRS I'd stick to the model frequency to get the maximum performance.


One update on the testings.
Last weekend tried it with the power set to 20dbm and indeed the range is nothing compared to before.
The day was not the best, cold, wet grass and foggy so definitely not the best conditions for RF, still it
went up to 350m with signal and I just didn't went more coz I was freezing. :)


Cool, I just test flew my multiwii tricopter last weekend, it's pretty awesome! I didn't bother with the PPM, too lazy. I think I will add a battery voltage warning to the telemetry when I have time.


Are you planning FPV?

My next step was to add RSSI out, probably use Timer2 to generate a 50hz pulse.
So it can either be used directly with some OSD's or with the buffers commonly used with FrSky and others RX's.


Been using it for some time but just realised I had forgot to share here. :)

Added support for output FrSky telemetry code from the TX module, so that I can use it with my modded 9X radio and see the RSSI levels from both RX and TX.

The yellow wire (seen in the picture above) goes from the pcb TX pin into the 2nd pin that after the radio mod works as RX for the FrSky module.
At the moment is only sending that data, but could potentially send anything that FrSky telemetry provides.


That is sweet! I will have to check it out. Do you lose your model settings if you flash different firmware to the 9x? I hope not.

I haven't done much because of the crappy weather and I have too many projects going on. Flew my tri for a bit, it's not properly tuned, but is still very nice. I am terrified of my HK450, but I can hover the tri around the kitchen. I will definitely setup FPV on it eventually. There's no way I will fly the 450 FPV. I have a 2.4GHz FPV system, but every time I turn it on to test it my house mates (probably neighbours too!)  lose wifi. Maybe I will get a 5.8 system. If you are thinking about DIY OSD, I have made my own ages ago, before kg4wsv made his MAX7456 lib (check out this very old and long thread http://arduino.cc/forum/index.php/topic,8785.0.html). You can probably use the same code in any of the arduino-MAX7456 OSDs sold everywhere.

I finally got around to edit the video of my autopilot test crash last year, you can see my OSD in action although replaying logged data: https://vimeo.com/58801611


Do you already have a different firmware or you're using the stock one?

Between different versions of er9x or open9x is possible to save them and after re-upload. I do that every time I update it just in case.
But try with the eepe tool it might even be able to save the ones from the stock fw.

Ehehe that is funny. :)
What's the power on that 2.4 vTX??? I also have helis (several... ) but never even tried to put FPV in them. For me FPV just in multicopters
with the tricopter been the best due to the fast tail response.
At the moment all the fun is going to my micro quad I converted to FPV: http://www.youtube.com/watch?v=7znVsR75TVc
I'm using a really old 1.3Ghz vTX so the range is super short and really bad video.

About the OSD I'll check it out, I have two E-OSD from HK and I'm using that but was considering getting one of the Arduino based ones with the
MAX7456. Last month almost lost my quad when I flew way out and got lost. :(
Btw, what tool did you used to overlay the OSD in the video? Or was just normal video overlay?


I think I have er9x. Flashing the firmware was the first thing I did when I got the radio, can't remember the option to save model memory. If er9x is compatible I will definitely give it a try.

My FPV Tx is 500mW, not that powerful, but much more than the 47mW or whatever the wifi router puts out! My next goal is to set up my tri for FPV, they look like so much fun to fly!

I'm pretty sure the HK Mini OSD is arduino and MAX7456 based: https://www.youtube.com/watch?v=hMUvrjivOQM. It's only $24.99 INCLUDING the GPS! That is ridiculously cheap. When I made my OSD they cost ~$100 without GPS. I wouldn't bother making my own these days.

Also did you see the HK 433MHz Open LRS thing? I guess Melih is not happy. I wish they copied my design so I can just buy it from HK instead of getting all the parts and building it myself  :D. It's fun soldering the first couple, now it's just annoying.


The option to save the models memories is with the PC tool EEPE (http://code.google.com/p/eepe/).

True, I was forgetting that. When I'm testing the gear at home I often have the radio next to the WiFi router but FrSky does hopping so it doesn't get too much into
the router. Now a vTX static in one frequency emitting with 500mW...
For video I've been using 900Mhz up to now, but I'm goign to try 5.8Ghz because the antennas are smaller and easier to fit in the multicopters.

I got a HK Mini OSD, it's using some custom FW. The problem is that they have a AtMega88, so there is very few space. I've loaded in mine the alternative FW cl-osd and it runs fine but even tried to port the arduino OSD code from Dennis @ RCG but was no good due to the size.
But the version with GPS is pure trash... including me I saw several people where the wires in the GPS were loose of badly soldered. I had to open mine to fix it.

I did saw. I actually got one... and I don't want to talk about it!  8)
Such a headache, my goal was more the TX as it fits nicely in the radio but it was a headache, tons of problems... eventually found out that during assembly someone
dropped a ball of solder on top of the RFM22B of the RX. :(
And I'm not the only one having problems, all sorts happening mainly due to bad soldering work.

Btw, have you ever tried the antenna diversity in the RFM22B? I was thinking in making a PCB with 2 antennas. It will require a RF switch.


Oh yeah EEPE I remember that now!

That's a shame about the quality issues. Did they really use a Atmega88? Damn my OSD code is 14k with arduino bootloader... Maybe able to squeeze out some stuff like the artificial horizon and make it below 8k... It's almost worth replacing the MCU with a atmega168.

Oh BTW I forgot to say that video I posted was done by recording just the OSD output while replaying logged data and overlaying it on the key chain camera video in the video editor.

I did think about diversity, but I don't know anything about RF to design a RF stage with switches. I was thinking about having 2 RFM22 modules on one PCB, which could also allow you to transmit and receive at the same time.


Thanks, when I saw the video i was like.. ouch! :S That was nasty. Glad you managed to retrive the gear.
I do like the OSD layout, the AHI seems to work quite well too.

I looked into the RFM22B docs, and they mentioned a RF switch.
Eventually I found that switch that works on 459Mhz and the design was rather simple. (making it work may prove different)

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