How to convert this duty to P1

T Chap · 2025-12-05 01:26

I want to see if there is a way to convert this to P1 so I can get a value ie 20% as the small one looks or 95% on the big one. Any ideas ?

T Chap · 2025-12-05 03:17

Better said, I want to see if I can send this signal direct to the propeller and convert it to a value 0-100. Counter?

throttlePin  = 0  ' whatever pin you wire it to

PUB MeasureDuty : dutyPercent
  dira[throttlePin]~        ' input

  ' Wait for a clean rising edge
  waitpne( |< throttlePin, |< throttlePin )  ' wait until low
  waitpeq( |< throttlePin, |< throttlePin )  ' wait until high

  t0 := cnt                   ' start of period
  waitpne( |< throttlePin, |< throttlePin )  ' wait for falling edge
  tHigh := cnt - t0

  waitpeq( |< throttlePin, |< throttlePin )  ' wait for next rising edge
  tPeriod := cnt - t0

  dutyPercent := (tHigh * 100) / tPeriod

JonnyMac · 2025-12-05 04:20

The recipe for fixed frequency PWM on the P1 is pretty easy, but it does require a cog. I've used the attached strategy to drive motors and LEDs and other devices that need fixed-frequency PWM.

Here's the outputs captured on my LA; frequency is set to 24kHz with ch0 set to 20% and ch1 to 95%.

T Chap · 2025-12-05 04:25

Thanks Jon, I’m sure I may have not been clear. I’m trying to connect something to the propeller that is outputting that signal on the scope so that I can read it into the propeller and convert it into a value inside the propeller.

JonnyMac · 2025-12-05 04:27

Sorry, I misunderstood. No problem, there is a counter mode that can be used -- let me look it up.

A few minutes later....

Found it. I created a dual pwm-read object for a TV prop that was controlled via wireless DMX receiver; my object could read the PWM signal from the receiver and convert it to a value between 0..255. For this demo I added a conversion in the main code to get 0..100. The reader object should work -- if not, it will give you direction in how to use the counters to measure pulses.

T Chap · 2025-12-05 04:47

Awesome! I will hook this up tomorrow and test it out thanks a bunch for posting this.

JonnyMac · 2025-12-05 05:13

My demo uses the pwm output from the first code I posted -- just disable that and connect your external signal to one of your PWM input pins.

Christof Eb. · 2025-12-05 18:01

This is an excellent document from Parallax:
https://obex.parallax.com/obex/propeller-p8x32a-counters-an001/

How to convert this duty to P1

Comments