Help with RC pulse to analog

SteveW719 · 2012-04-12 10:02

HI,

I am wondering if anyone is familiar with a propellor object to measure the servo control pulse width out of an rc receiver (usually 1000 to 2000 msec) and convert it to a 0-10v or 4-20ma loop for use with some industrial type drives. Also if there is a Prop board available with analog output onboard.

Many thanks

S

Duane Degn · 2012-04-12 10:19

The posts in this thread might help.

http://forums.parallax.com/showthread.php?139341-trying-to-tie-an-r-c-receiver-output-to-pwm-motor-control

Could your analog output be in the form of PWM?

SteveW719 · 2012-04-12 10:53

Thanks for pointing me in the right direction. I will need an analog 0-10vdc not a PWM signal.

JonnyMac · 2012-04-12 13:52

You can filter the PWM signal and buffer with an opamp.

Ariba · 2012-04-12 20:03

With the help of the Propeller counters you can do that without objects and with only a few code lines:

CON
  _clkmode  = xtal1 + pll16x
  _xinfreq  = 5_000_000

  INPIN  = 0      '<-- pin numbers
  OUTPIN = 1

PUB Main : puls
  ctra := %01000<<26 + INPIN    'POS detect mode for pulse in
  ctrb := %00110<<26 + OUTPIN   'DUTY mode for Analog out
  frqa := 1
  dira |= 1<<OUTPIN
  repeat
    phsa := 0
    repeat until phsa > 0       'wait for high pulse
    waitcnt(clkfreq/500 + cnt)  'wait 2ms to get entire pulse
    puls := phsa                'pulslength in clock ticks
    puls -= clkfreq/1000        'subtract 1ms
    puls := puls * 4095 / (clkfreq/1000)  'scale 1ms to 0..4095
    frqb := puls << 20          'scale to DUTY range (32bits)
    'you get 0..3.3V output at OUTPIN
    'add an R-C lowpass with ~10Hz cutoff
    'and then an OPAMP with a gain of 3 to get 0..10V

This is absolutely untested!
For a first test you can measure the voltage at the OUTPIN with a Multimeter you should get 0..3.3V for 1ms..2ms pulses.
To get a 10V output you need a filter and an OPAMP. Here is a possible circuit:

Andy

Help with RC pulse to analog

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