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Attention: RC-CAM.com will be closing down August 2021.

The RC-Cam.com forum was the very first online community dedicated to the advancement of wireless video cameras on radio controlled (R/C) models. This is now called "FPV" (First Person View). We are proud of the contributions that our members have made to the FPV hobby.

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Hello Everyone,

I am trying to find information on how I can use 1 channel and split it into about 8 momentary switch functions on the model. I know that a company called MCD makes one with 8 and one with 16 functions. My problem is that I need a custom Keypad layout. I tried to contact MCD but their web site is down. I want to make my own using an Atmel micro controller. I can do the programing. I just don't know how to interface it into the radio. Has anyone done something like this? Any help would be appreciated.



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Can't you just take the MCD keypad, remove the switches, place them how you want on a separate board and wire them back? Sounds like the easiest solution.

The radio input is intended for a potentiometer and has 3 wires, +,- and wiper. The positive voltage is usually 5V, and the pot acts as a voltage divider giving 0-5V on the wiper pin.

So either you can make a resistor network with the switches at the middle points in order to have a different output voltage for each key combination (basically a wired DAC), or you use a microcontroller to sample the switches and interface it to a "real" DAC or digital pot chip that will be connected to the radio's input.

Now, with 8 switches (256 combinations and thus different output voltages, not including a needed margin not to confuse codes and get a wrong output) you risk outresolving the transmitter. So you'll need to use the 2nd solution with an MCU, implement some protocol (which MCD most likely did), by sending sorts of digital words encoded into successive voltage levels that the receiver will buffer and decode.

I'd say you can safely divide the 0-5V range into maybe 16 steps if you don't want to have to implement a calibration procedure, sending 4 "bits" at a time. So with a little more for error detection it would take 3 transmission cycles to send an 8-switch combination.

At that point either you develop a decoder yourself or you try asking MCD how their protocol works and make a compatible encoder, or even ask them for a custom keypad, but I'm still sure the keypad rewiring is the simplest option ;)

Edited by Kilrah
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