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16  Community / Exhibition / Gallery / Problem with my board! on: November 09, 2012, 11:59:31 am
Hi guys,

Just to let you know that I found a problem with my board design. It the way I am using the resistor dividers to shift 5V from arduino to 3.3V for the RFM22. Because I have modified the RF22 library to run at very high speed, the resistors and the capacitance of the traces begin to act like a RC filter. This can corrupt the SPI data, causing lockups. This means that the SPI bus is operating very close to the limit, voltage problems with power supply can easily cause a lockup, especially if you run a lot of servos. If you only use the board for spec scan or telemetry you may not have this problem at all.

As you can see here, the SPI clock out from arduino (blue) is distorted when it gets to the RF22 module (yellow). This screen shot is a bit exaggerated because I was using X1 probe, it's better with X10.




Solutions:

1. Software solution: reduce SPI speed, change the SPI speed down to 2MHz in the RF22.cpp file. Change the line in RF22::init() to SPI.setClockDivider(SPI_CLOCK_DIV8);
2. Hardware solution: reduce resistor values. I tried halving the resistor divider values (R2 - R7), and it works much better. Replace 1K with 470 Ohm, and 1.5k with 680 Ohm.
3. Both. <-- I recommend this for best reliability
17  Community / Exhibition / Gallery / Re: Cheap UHF spectrum analyzer (and RC tx rx) using RFM22 module on: October 25, 2012, 04:25:50 pm
$110 is a lot of money. I don't think he will be able to sell many at that price considering that you can just get this: http://www.hobbyking.com/hobbyking/store/__24965__RMILEC_TS4047_10CH_2_5W_UHF_Module_System_w_Receiver_JR_module_.html $180 with diversity receivers.

A bit of a update, I lost my glider while testing autopilot. Stupid mistake, pulling too hard out of a dive. So I had to get a new one, spent all summer trying to get that flying. During that flight I was able to log RSSI vs distance, you can see the plot. I didn't go very far, only 200m, but if I extrapolate the trend I will probably start to get occasional packet drops at 1km and lose signal completely at 10km.

On the RF22 front, I have managed to get telemetry working on my boards, and fixed some bugs, unfortunately also introduced some new ones that causes the board to lock up randomly and other weird problems.
18  Community / Exhibition / Gallery / Re: Cheap UHF spectrum analyzer (and RC tx rx) using RFM22 module on: October 06, 2012, 08:14:53 pm
I'm not sure you can change output power with voltage. Some versions of the datasheet says you can change power from 1dBm to 30dBm with register settings, just like the RFM22, however, the datasheet on hoperf website has incomplete info...

19  Community / Exhibition / Gallery / Re: Cheap UHF spectrum analyzer (and RC tx rx) using RFM22 module on: October 04, 2012, 07:30:48 pm
Hmm... very interesting... looks like they use the same SI chip with some RF power amp or something, so it should work. There are probably a few things that need to be changed in the code, obvious stuff like power level setting. You do need to be aware that the thing draws 550mA during transmit, so you will need a switch mode BEC or something to power it. It can run on 3.3 to 6V, so that's good.

It is possible to use a RFM23 as the tx and the (probably cheaper) RFM22 as the rx, so you can reuse the rx boards. This is very cool!

Any ideal on prices and availability??


20  Community / Exhibition / Gallery / Re: Cheap UHF spectrum analyzer (and RC tx rx) using RFM22 module on: July 20, 2012, 11:35:23 am
Yes, it's a v2 board. I have converted all my RC aircraft to UHF. Working great so far, although I've only been flying line-of-sight.
21  Community / Exhibition / Gallery / Re: Cheap UHF spectrum analyzer (and RC tx rx) using RFM22 module on: July 19, 2012, 05:54:20 pm
No worries! Good luck with the house move!

Hopefully in the next couple of months I will have done some definitive in-flight range tests, using a modified ardupilot code that runs on this RF22 board and log RSSI vs distance. It is more or less working, just waiting for better weather for a proper test: https://vimeo.com/43210881
22  Community / Exhibition / Gallery / Re: Cheap UHF spectrum analyzer (and RC tx rx) using RFM22 module on: July 19, 2012, 04:40:42 pm
Oops. I have a feeling that the jitter is caused by the negative PPM used by Futaba. You can try changing "attachInterrupt(1, ppm_fun, RISING);" in your Tx PPMInitialization(); function to "attachInterrupt(1, ppm_fun, FALLING);". I didn't think about that since my 9x uses positive PPM.

You should confirm that works by connecting your Rx to the computer and start serial monitor at 38400 baud. It will print the first 8 channel values in us*2 (0.5 us resolution). If all the values are stable and in the 2000 to 4000 range then it should be safe to connect a servo to it. You can use my plotting program http://arduino.cc/forum/index.php/topic,80462.msg607817.html#msg607817 to visualize and noise and/or jitter.

I'm not sure what's up with your Pro Mini board. Does it work in spectrum analyser mode? 3.3V to GPIO2 is the high power (20dB) mode, with the red or whatever colour LED you soldered to D1 as an indication. I think if you leave the jumpers unconnected, it defaults to high power mode, which I added as a safety feature.

Edit:

Oh, also all of my code seem to work fine with arduino 1.0.1. I would suggest everyone change to that, since they fixed hardware serial and some servo bugs.
23  Community / Exhibition / Gallery / Re: Cheap UHF spectrum analyzer (and RC tx rx) using RFM22 module on: July 18, 2012, 09:21:38 am
That doesn't work, pin 3 just needs pulling low to turn on the RF LED on the front panel of the Tx (a 1k resistor works fine).
For example, OpenLRS controls pin3 via Arduino and code.

I can use a 10k pullup resistor between pin1 (PPM) and pin2 (Tx battery voltage) and get around 10v PPM - waaay too much!

I think I'll try a pullup resistor between PPM and the 3.3v onboard regulator of my ghetto module.


Any other ideas? (other than using the trainer port, which is not an option for module useage).

Nigel.

Wait so you are able to get PPM out but it's 10V? So can't you just use a voltage divider to drop it to 3.3V?

Edit:
OK ignore that. So basically the PPM output is active low or open collector or something? It's probably not good for the radio if you feed 10V through it. In that case pulling it up to 3.3V will work, or alternatively you can add "digitalWrite(3, HIGH)" inside the PPMInitialization() function after "pinMode(3,INPUT)", to turn on the 328's internal pull-up.

Also I just got my new boards back. They are 37x48mm, and seem to fit into my 9x module box (34x54) if I put them in at an angle. I'll put some pictures up later.
24  Community / Exhibition / Gallery / Re: Cheap UHF spectrum analyzer (and RC tx rx) using RFM22 module on: July 10, 2012, 01:29:56 pm
If you can confirm that a 50x33mm board will fit inside your Futaba module it will be great.

I think you will have to solder your own connectors, because I'm pretty sure JR and Futaba pins are different.

I may look into smaller SMD versions if there people are interesed.
25  Community / Exhibition / Gallery / Re: Cheap UHF spectrum analyzer (and RC tx rx) using RFM22 module on: July 05, 2012, 04:12:41 pm
Huh so futaba and JR use the same size boards...

A 50x33mm board is definitely doable with through hole 328, I can start working on it if you still want one. We can split the cost of ~£20 for 10 boards.

Which pro mini do you have? If you have the 5V version you will need to use a 3.3V reg for the RF22, and some resistors to divide the arduino SPI output to 3.3V. It could be quite simple if you have the 3.3V version, but I am not sure if my code will work at 8MHz.
26  Community / Exhibition / Gallery / Re: Cheap UHF spectrum analyzer (and RC tx rx) using RFM22 module on: July 05, 2012, 03:30:16 pm
I would really like to build your Spectrum Analyser. Could you please tell me where to find the component layout etc of your board. I see a comment in this forum that the schematic is "attached", but i cant see where it is attached. Sorry to be so stupid. You also offered to send a copy of the board to someone. I would really appreciate this. My email is Ngakuta1@xtra.co.nz Thanks a lot.

Unfortunately I don't have any boards left right now. I will let you know I I get the new ones back from China.

You should be able to see the attached files now that you've joined the forum!
27  Community / Exhibition / Gallery / Re: Cheap UHF spectrum analyzer (and RC tx rx) using RFM22 module on: July 04, 2012, 06:00:58 pm
Wait are you sure you measured the Futaba modules?

I have a 9X which I think uses JR modules, but also measures 54x34??
28  Community / Exhibition / Gallery / Re: Cheap UHF spectrum analyzer (and RC tx rx) using RFM22 module on: July 04, 2012, 05:38:04 pm
I think I can do 50x34 with the 28 DIP package. If I make a board 34mm wide, will it fit? Or should I make it 33mm just to be safe? If it needs to be much smaller I will have to go SMD.

I will need to redesign the board completely though. I pretty sure I need to add a 5V regulator as well. It might take a while...

Also you probably will have to drill holes and what not in your case to mount the connectors, LEDs and switch externally.

29  Community / Exhibition / Gallery / Re: Cheap UHF spectrum analyzer (and RC tx rx) using RFM22 module on: July 02, 2012, 04:58:07 pm
Hi Zitron,

I'll take one of your new boards as it'll just about shoehorn into the Futaba T9C module cavity.
PayPal OK?
I have enough components to build onto the board.
Real shame you couldn't get it to fit inside a Futaba Tx module case smiley-wink

Nigel.

Have you got the inside dimesions of the Futaba module? Is it the same as the 9X ones? I haven't sent the files to be manufactured yet so it is possible for me to change the designs and make it even smaller.

I can also try to make a tx only version, which will be much smaller.
30  Community / Exhibition / Gallery / Re: Cheap UHF spectrum analyzer using RFM22 module on: July 02, 2012, 08:20:45 am
Nice little board. How much are they?

Probably £2-3 each depending on whether you want them coloured, and thickness.
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