Cheap UHF spectrum analyzer (and RC tx rx) using RFM22 module

[Mauzer]

edit: BTW did you manage to get it working?

Not yet. Waiting for RFM22 boards...

[Dfidalgo]

These boards looks great! 

BTW I don't know if anyone would be interested in this, but I have found that the RF22 library is not compatible with timer based hardware servos. Very weird and hard to debug. It is because the interrupt driven read function takes too long, messing up servo PWM timings. I had to modify the library quite a bit, but now I have hardware servos! If anyone else have problems with the servo library I'll let you know what to change.

Can you upload your modifyed library or explain here what to change?  Did you solved the glitches issue with this mod?

Regards

[zitron]

I'd be interested in buying a booster pcb from you (same layout as Melih for the same chip), maybe if you could design it in a way that the resistors, caps, diodes,  etc would be of a bigger size, for easier diy work...Do you manufacture these pcbs by yourself?

Yeah except I really don't know much about RF design... If I tried to make one of those high power amps it would probably catch fire!

[zitron]

Can you upload your modifyed library or explain here what to change?  Did you solved the glitches issue with this mod?

Well I fixed the glitch problem awhile ago by using software servos, now hardware servos are also working, which is more processor efficient.

I will try to release a simple "reference" code sometime next week, it will include all the libraries, and will be a simple PPM->Tx->UHF->Rx->Servos thing.

Edit: Important notice, please make sure that you can find a 5V source on your radio, this board does not have a voltage regulator for the arduino, so you can not power it direct from your TX battery. 

[Dfidalgo]

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Edit: Important notice, please make sure that you can find a 5V source on your radio, this board does not have a voltage regulator for the arduino, so you can not power it direct from your TX battery. 

Well, my TX is a Graupner MC-19, I think that a LM7805 can solve the problem dont?  Anyway, I do intent to use your tx uhf with a joystick that generates the ppm signal from another arduino (details here: http://www.ianjohnston.com/content/index.php?option=com_content&view=article&id=30:project-rc-ppm-trainer-port-joystick) I have done this on my homemade console that you can see here at work:
http://www.youtube.com/watch?v=wIUw7Lfdme4

The joystick will be a old but cool "Top Gun" , and a pair of old T2m rudder pedals, all for FPV obviously.

[Dfidalgo]

Yeah except I really don't know much about RF design... If I tried to make one of those high power amps it would probably catch fire!

Don't worry man, i have a uncle that is firefighter ...      If you make one RF booster, I'll test for you!  XD 

[msev]

Yeah except I really don't know much about RF design... If I tried to make one of those high power amps it would probably catch fire!

No need to worry about that since at would be runing it at 1/7 of its total output power and in such conditions you dont even need a heatsink for the chip..

[zitron]

The joystick will be a old but cool "Top Gun" , and a pair of old T2m rudder pedals, all for FPV obviously.

Wow that is pretty cool, and yes LM7805 will work fine, that's what I use. The board draws very little power.


Also I thought I should update the schematics and bill of materials, there are some slight changes. See attached.

[zitron]

No need to worry about that since at would be runing it at 1/7 of its total output power and in such conditions you dont even need a heatsink for the chip..

One step at a time, let me get this simple board working properly first!

[msev]

One step at a time, let me get this simple board working properly first!

You are right! It will take me a lot of time till I'm at the stage to start building olrs....since I intend to first try and play with a diy 2.4ghz booster based on rf2126 chip...

In the meantime I'd like to ask you, which vreg could be a suitable replacement for the one Melih uses - mic5205...I read the datasheet and saw it has a really low dropout voltage or something like that..Is there any other which has a low dropout voltage but a higher maximum current?

So you use LM1117?

Regarding Melihs design besides powering the atmega and rfm22, does anything else use power (maybe the driving of the servos? and if so do they use such a small amount)? Because that mic5205 has a small max current..
Thanks!

[zitron]

In the meantime I'd like to ask you, which vreg could be a suitable replacement for the one Melih uses - mic5205...I read the datasheet and saw it has a really low dropout voltage or something like that..Is there any other which has a low dropout voltage but a higher maximum current?

So you use LM1117?

Regarding Melihs design besides powering the atmega and rfm22, does anything else use power (maybe the driving of the servos? and if so do they use such a small amount)? Because that mic5205 has a small max current..
Thanks!

The RF22 only draws 85mA at full power, plus maybe 20mA for the atmega. Also the transmission only happens in quick bursts so it's not always on. The mic5205 should be plenty, since servos are powered separately from the BEC. I think any regulator will work as long as the drop out voltage is not much more than 1V, obviously lower is better to prevent brownouts.

[msev]

The RF22 only draws 85mA at full power, plus maybe 20mA for the atmega. Also the transmission only happens in quick bursts so it's not always on. The mic5205 should be plenty, since servos are powered separately from the BEC. I think any regulator will work as long as the drop out voltage is not much more than 1V, obviously lower is better to prevent brownouts.

Thanks! you gave a very clear answer ...Why does flytrons TX module have 2 vregs, mic5205 and a LM2937?

[Dfidalgo]

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?

Regards

[zitron]

Thanks! you gave a very clear answer ...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.

[msev]

Yep two vregs, one normal and one ldo...Is it because of the buzzer, since thats the only additional element added.