3D Robotics Comment by Chris Anderson on December 23, 2008 at 12:46pm

All of our code is to read PWM, but you're talking about PPM. PWM is the signal that goes to the servos. PPM can only be read if you tap a special pin on the chips in older (non spread spectrum) RC receivers.

(see this from the Paparazzi site for a fuller explanation)

Which did you mean?

Comment by James Holbrook on December 23, 2008 at 1:05pm

Thank you Chris. What I am referring to is to be able to read the pulse that leaves the receiver and goes to the servos. I have modified my receiver to be able to attach the output stream to Pin 8 and I also have tried pulseIn as you all do. PPM PWM whatever it is. I need to be able to read it on the Serial Monitor to see the changing values as the sticks/knobs are moved. I would be using serialPrint to the screen. In the RC Test code, I thought this might be useful and meet my basic need, but the motor control stuff threw my brain into a tizzy.

Have looked at the Paparazzi link you mentioned and thank you. Still the question remains to be able to see the pulses on Serial Monitor.

3D Robotics Comment by Chris Anderson on December 23, 2008 at 1:34pm

Ah. Okay, you mean PWM. Big difference (can you correct the post title and body so people aren't confused?)

When you run my RCTest code, it should be sending Channel 1 and Channel 2 readings to your serial monitor. (Ignore all the motor stuff--it doesn't matter if they're connected or not). Are you seeing those?

Comment by James Holbrook on December 23, 2008 at 2:07pm

Hey Chris.

The setup is my receiver is on, the servo pins are connected to pins 5&6. When I start the code it states: Ready.
Then is says Channel 1: 0
Initial Throttle: 1497
Channel 2: 0
0 -224
Initial Steer: 0
Channel 1: 0

then on the next cycle it just repeats endlessly.

Any Clues? The receiver drives servos fine on all channels.

Jim

3D Robotics Comment by Chris Anderson on December 23, 2008 at 2:21pm

It looks like I may have commented the code wrong. The code I'm looking at shows the RC input is on pins D6 and D7:

Channel1Value = pulseIn (PD7, HIGH, 20000); //read RC channel 1
Channel2Value = pulseIn (PD6, HIGH, 20000); //read RC channel 2

Comment by James Holbrook on December 23, 2008 at 2:23pm

Hold the train Chris,

Got it to read the pulses now. I had followed the pinout in the code but the pin numbers didn't match up and once I connected to PD7 to D7, it started working. Now Do I just repeat the code for these two channels for the next two channels so I can read channels 1-4 on the serial monitor. This code is based on Servo or Servotimer1?

Jim

3D Robotics Comment by Chris Anderson on December 23, 2008 at 2:42pm

It's based on the Servo library. It takes about 20-30% of available CPU capacity to read each channel, so you'll find that reading four channels slows down the code a lot. Servotimer is more efficient but is limited to just two channels.

Comment by quix-fz on December 24, 2008 at 11:16pm

http://diydrones.com/profiles/blogs/705844:BlogPost:39393

this will read the sum-ppm-signal of all channels, without using any cpu (less than 1%). can easily be modified to read one channel, or any other number you like (by ANDing all the channels you want to read)

3D Robotics Comment by Chris Anderson on December 24, 2008 at 11:59pm

@quix: If I'm not mistaken, getting that PPM signal requires soldering a wire in the RC receiver, and as I recall doesn't work with modern spread-spectrum receivers. Is that correct?

Comment by quix-fz on December 25, 2008 at 3:09am

@chris: that's correct. but ORing the signals (not anding as i wrote before) could still work...

it just seems very wrong to me to use that much cpu time waiting for a signal....

i think a saw a simple port expander ic, which had a input-capture function for each pin... i'll see if i can find it again...

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