speed control

[Kees Reedijk]

I want to do simple speed control of a small dc motor with gearbox and optical encoder. Proportional control will be accurate enough, only one direction. Since the motorspeed will be quite low I thought of using the pulsin command to measure pulse length for the feedback.
Has anyone done this before?
thanks

[mister_e]

you can use pulsin for sure... if you read few times and do an average, it can provide great results if your pulses are short enough to avoid an overflow of pulsin variable.

BUT i'll prefer to convert pulses to voltage and read from a/d converter.

have a look to this thread can give you some hints...
Click Here

[Kees Reedijk]

Thanks Steve
Today I managed to get it working using the pulsin command. I use a surplus maxon motor with a 32 step optical encoder, pulse length is not a problem. It works really well. I'm using a pic16F628A.
Here's part of the code I used:
p.s.for some reason all my indentation disappears when I posted this message, don't know why
regards, Kees

motor CON 3
sensor VAR PORTB.0
temp VAR WORD
setspeed VAR BYTE 'speed set by user
power VAR WORD 'control variable (CV) , PWM dutycycle
PV VAR WORD 'process value, or actual speed
error VAR BYTE 'difference between set speed and actual speed
Kprop VAR BYTE 'constant for proportional feedback control
Kprop = 4

run:
Pot 5,25,setspeed
PulsIn sensor,0,temp ' measure speed
IF temp2 > 0 Then ' check if motor is running
PV = 10000 / temp ' depends on encoder and motor
IF PV >255 Then PV = 255
IF setspeed > PV Then
error = setspeed - PV
power = power + (error / Kprop) 'new PWM value
IF power > 255 Then power = 255 'otherwise overflow
Else
error = PV - setspeed
power = power - (error / Kprop) 'new PWM value
IF power > 255 Then power = 0 'otherwise overflow EndIF
Else
power = setspeed ' so a motor without optical sensor
EndIF ' can also be used
HPwm motor,power,10000 ' Send a PWM signal at 10kHz, drive motor
LCDOut $FE,1,"spd ",DEC3 setspeed 'show on screen
LCDOut $FE,$C0,"pv ", DEC3 PV 'for debugging
GoTo run

[mister_e]

hi kees, great to know that's working for you now.

p.s.for some reason all my indentation disappears when I posted this message, don't know why

must use VB code click here to know how

after that your code can look something like that

motor CON 3
sensor VAR PORTB.0
temp VAR WORD
setspeed VAR BYTE 'speed set by user
power VAR WORD 'control variable (CV) , PWM dutycycle
PV VAR WORD 'process value, or actual speed 
error VAR BYTE 'difference between set speed and actual speed
Kprop VAR BYTE 'constant for proportional feedback control
Kprop = 4

run:
     Pot 5,25,setspeed 
     PulsIn sensor,0,temp ' measure speed 
     IF temp2 > 0 Then ' check if motor is running
          PV = 10000 / temp ' depends on encoder and motor
          IF PV >255 Then PV = 255
          IF setspeed > PV Then
               error = setspeed - PV
               power = power + (error / Kprop) 'new PWM value
               IF power > 255 Then power = 255 'otherwise overflow
          Else
               error = PV - setspeed 
               power = power - (error / Kprop) 'new PWM value
               IF power > 255 Then power = 0 'otherwise overflow EndIF 
     Else
          power = setspeed ' so a motor without optical sensor 
     EndIF ' can also be used

     HPwm motor,power,10000 ' Send a PWM signal at 10kHz, drive motor 
     LCDOut $FE,1,"spd ",DEC3 setspeed 'show on screen
     LCDOut $FE,$C0,"pv ", DEC3 PV 'for debugging
     GoTo run

and once it's done, it appear that there's one ENDIF missing