9 replies to this topic

[stefan.barlow]

Hello, first day with the Netduino but several years of experience with C#. I am not very experienced at all with circuits so I need some guidance. As my first project I'm looking to hack an RC controller to replace a pair of stick pots with the Netduino. So far I am understanding this can either be done with a digital pot or PWM. The pots are both 3 wires. Measuring across the outside two wires on forward / reverse pot at 2V DCV is 1.0. The mid mark is .5 when measuring the middle wire. The steering pot is measuring 6 across the outside, 3 in the middle with the meter set on 20V. My first questions are: Would PWM require some resistors and other components? What would the wiring look like with the proposed solution? Thank you for your help! Stefan

[Chris Walker]

Hi Stefan, You can probably use PWM, but you may need to "smooth out" the digital wave output into a more analog signal. An external DAC will work as well. The other thing to ensure is that you're driving the proper voltage and current. The Netduino drives 3.3V signals, but it looks like you may need to increase that voltage a bit. Welcome to the Netduino community, Chris

[stefan.barlow]

Thank you Chris, I did some more digging and it appears I need to use a capacitor to handle the smoothing if I understand correctly. If I can increase the voltage would I just need to wire it into the signal input for the pot and leave the +/- alone? Thank you! Stefan

[Thomas]

Hi, You could also use a digital potentiometer like http://www.maxim-ic....vp/id/4205/t/al /Thomas

[stefan.barlow]

With your feedback to aid my googling I found this topic on another site and this looks like exactly what I need for the low pass filter. http://www.arduino.c...?num=1254389797 It includs a monitor input back into the analog in. Thanks for the help! Stefan

Attached Files

•  schematic5.jpg   16.89KB   39 downloads

[stefan.barlow]

I built the filter as diagrammed and it works great, I do need to boost the top end to 6V now so that will be the next task.

[stefan.barlow]

I've come to find out using a 'scope that the transmitter is actually using PWM to control the RC vehicle. It is at about 200hz with the pulses at a full 9V. If I had more control over the PWM settings of the Netduino I could simply replicate the timing and amplify the output. I tried doing it in code but I believe I may need sub-ms resolution, though I have a few more things to try. How is the PWM implementation on the new firmware coming along? That would make this so much simpler at this point I believe.

[bill.french]

Can you better describe what you are trying to do, what you're wiring up, etc? I have some ideas.

[stefan.barlow]

Bill, I had intended to interface the Netduino with a toy grade RC controller to control an RC car from the PC. I have longer term plans that include the typical autonomous vehicle sensors and wireless control, this was just the first step and I was trying to start cheap and add components as I got more comfortable (XBee, motor controllers, etc). I think at this time the best route would be to simply ditch the transmitter and go straight for a motor control board and replace the RC's built-in board entirely. The cheap route didn't work so well. lol Thank you for your time.

[bill.french]

Instead of a motor control board (some sort of shield, I am imagining?), you might pick up an RC ESC and control that with pwm. Http://www.hobbyking.com has tons of cheap stuff. What toy RC is it?