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Dimitris76

635 Diversity Rx board

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This is my second attempt to make the Airwave 635 Rx work. On the first one I ended up with a fried up module - without even having the pleasure to see some smoke, flame - something spectacular at least....

That left me troubleshooting for hours before officially declaring it dead and start looking for a new one, which I couldn't find anywhere, until Oxxyfx from nghobbies.com hooked me up with one recently.

With the module on the way, I am trying to figure out what went wrong and I have pinpointed the error on the lack of a diode. Specifically I didn't install the D1 diode, so when the Led Control pin 13 was high it was shorted to the ground through the NPN transistor.

Anyway, with the extra diode in place do you guys see any other problems/faults with the circuit?

The IC is a NE555 timer in monostable form, that activates a buzzer when the reception switches between the antennas. The one pot in line with the buzzer controls the volume, the other how long the buzzer sounds. I am thinking like 0.1-0.2sec will be nice - it will sound like a short chirp right?

The two leds on the schematic's far left side are flashing alternatively according to the antenna that receives.

Thank you for your comments!

Dimitris

Schematic1.pdf

V1Board4.pdf

Edited by Dimitris76

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If the chirp circuit indeed caused the problems with the first attempt, then it might be best to not stuff those parts until you have the Rx working correctly. That will eliminate any doubt if you run into problems again.

The one thing I noticed is that the 7805 seems to only have bulk caps on it. I would suggest a 0.1uF ceramic cap on its output pin too.

From the looks of the Antenna's stripline feedpaths, I would say you plan to use 0.8mm FR4. Is that correct?

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Mr RC-Cam,

I was hoping you'll chime in for advice!

The actual receiver part of the circuit is not a problem - I have already built and tested a PCB for the 634 receiver that works perfectly. It's the sound and light effect department that worries me (the schematic on first post) - because of my previous failed attempt...

The 7805 has a 470uF/25V electrolytic on input/output plus a 33uF/10V low ESR tantalum on the output. It's a SMT component placed on the top side, so it might not be too obvious...

I am attaching the zipped Eagle board file.

The stripline is 1.8mm (or 76mil) wide on 1mm thick, 0.035mm copper plated FR4. That should give according to the calculators approximatelly 50 Ohm impedance.

Dimitris

V1Board4.zip

Edited by Dimitris76

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I still think that it would be wise to build your new 635 project without stuffing the buzzer related components, then add them after the Rx is validated. That way if things don't go as planned, you will be able to better determine what may have caused the grief. The reason I say this is because I have a hunch that shorting the LED control output to gnd, through the transistor, would not have prevented the first 635 project from receiving a signal. I could be wrong, but you know those hunches. :)

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