Posted by Chris Anderson on December 11, 2009 at 10:52pm
The best way to read RC signals is PPM, which is a sequential stream where each channel is output in turn on a single wire. But traditionally the only way you can get that is to open up your RC receiver and solder a wire to a special pin. Fortunately the Paparazzi team designed a board that will convert up to 8 channels of regular PWM servo signals to one PPM signal, with no RC hacking required. We've now modified it a bit to work with our failsfe multiplexer and released a version as a DIY Drones product ($24.95).
BTW, the forthcoming ArduPilot Mega will use this technique, as well.
From the product description:"This improved & reduced PPM encoder board, based on a Paparazzi design, plugs into the servo output ports on a R/C receiver and encodes them into a PPM pulse suitable for the paparazzi autopilot and other projects. This allows you to use any R/C equipment with the paparazzi autopilot or read up to 8 servos with a single I/O pin of your uController. Modifications to the R/C receiver are not necessary. Connect the wires from your receivers channels to the PPM and one wire to the PPM in of your system. If you decide to use the tiny board to power the receiver, make sure you put-in a jumper and plug something between the 8th channel and the receiver.
The whole project is based around the ATMEL ATMEGA168/328 AVR processor and all timing is done
within interrupts so accuracy and stability is optimized
It is now also possible to select the PPM waveform shift, negative or positive.
Firmware is free and was created by Hendrix and Moa, with tiny modifications by Jordi Muñoz that allows control an extra failsafe multiplexer.
I've just found when testing with the rx that if I hold my roll stick far right on startup then I get the expected led blinking, so it's looking more like sofware/config than a hardware fault.
Khalid/Markus, maybe try starting up with various stick positions to see if anything happens?
I'll have to look further into whats happening, I suspect the output of my rx may not be what the software is expecting - I'm using a frsky module and rx on a futaba 9c.
Since I'm an ignoramus, any pointers or thoughts would still be very welcome, thanks!
OK, I have tx and rx on servo inputs one and two (tried both ways round, of course, but I know what it should be), 5v power via the usb ttl adapter, jumper on pins 4 & 6 of the programming pins.
The usb ttl adapter has leds for tx and rx, when I power cycle the ppm encoder I would expect the adapter rx led to flash regardless of my terminal settings. It does not, whereas if i connect usb adapter tx/rx together and type chars in the terminal both tx and rx leds light, as expected.
Thanks Chris.
Yup, that's what the docs say should happen. Mine was sitting there with the LED on continuously, no flashing, all channels connected to a bound and working (checked with servo on throttle channel 3, which I believe is the important one) rx. I'm not sure what else to check / test, I have no oscilloscope available, just an old but OK multimeter. Only just got home, so not checked the ppm output yet after flashing 4.3 firmware.
Markus, Is there a reason that you soldered onto, rather than through the holes? Structurally you are at risk of pulling off the traces. Electrically you are assuming that there is no electrical connection on the back side of the through-hole and/or that the hole is successfully plated through. I don't know what you are soldering with that destroyed the insulation on those wires, but over in Europe you ought to be able to pick up an Antex (they're UK) 12W or 15W pencil iron with the smallest available chisel tip for the price of a bottle or two of good, daily table wine, then put those wires *through* those holes. Sorry, I can't tell if you have the power jumper correct.
Same here, blue LED on the whole time, no ppm output. Also, nothing when jumpered for serial connection.
Flashed latest firmware via ISP, still no serial connection. Will test it for ppm later today, but I'm beginning to come to the conclusion it may be faulty.
The LED is really supposed to blink? Mine stays on all the time and this is the second encoder I tried (sent back the first one because I thought it might be damaged). Is this the right way to connect it? I can't find any documentation :) I tried every input port without any other results. http://www.die-kreuzzuege.de/P1000436.JPG
It wont put out any waveform unless there is servosignal in on the falesafe input. I think it is input number 3. If you are just using some inputs then you can connect the unused inputs together with one with input signal.
Quick question for the gurus. I've got the encoder hooked up to a Futaba receiver. I can scope the signal going into the board, however, there is no output signal being generated. The blue LED on the board is on (not flashing). I've tried it with FASST/PCM/FM receivers with no luck. I've reflashed the board also and that didn't help. Any thoughts?
Comments
Khalid/Markus, maybe try starting up with various stick positions to see if anything happens?
I'll have to look further into whats happening, I suspect the output of my rx may not be what the software is expecting - I'm using a frsky module and rx on a futaba 9c.
Since I'm an ignoramus, any pointers or thoughts would still be very welcome, thanks!
The usb ttl adapter has leds for tx and rx, when I power cycle the ppm encoder I would expect the adapter rx led to flash regardless of my terminal settings. It does not, whereas if i connect usb adapter tx/rx together and type chars in the terminal both tx and rx leds light, as expected.
Yup, that's what the docs say should happen. Mine was sitting there with the LED on continuously, no flashing, all channels connected to a bound and working (checked with servo on throttle channel 3, which I believe is the important one) rx. I'm not sure what else to check / test, I have no oscilloscope available, just an old but OK multimeter. Only just got home, so not checked the ppm output yet after flashing 4.3 firmware.
Flashed latest firmware via ISP, still no serial connection. Will test it for ppm later today, but I'm beginning to come to the conclusion it may be faulty.
http://www.die-kreuzzuege.de/P1000436.JPG
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