Hooking up Potentiometer to Servo

annamaria

Im trying to write a bit of code where I can control a servo with a potentiometer. I want to be able to move it to any angular position +/- 80degrees from the centre position. I should then display this position to the screen as it rotates.

Does anyone have any idea where I can start with this? I literally have no idea how to get the potentiometer to interact with the servo. Any bit of code would help to get me started!

Thanks

tomcrawford

Have a look in whats a micro controller.. In my copy (version 2.2), chapter 5, activity 4 should help.

kwinn

First thing to do is figure out the mechanical linkage. Then you need to determine the position. The simplest method to do that would be using the potentiometer as part of an RC circuit.

annamaria

tomcrawford wrote: »

Have a look in whats a micro controller.. In my copy (version 2.2), chapter 5, activity 4 should help.

' {$STAMP BS2}
' {$PBASIC 2.5}

time VAR Word
PAUSE 1000

DO

HIGH 7
PAUSE 10
RCTIME 7,1, time
time= time */ 185 'scale by 0.724 x 256
time= time + 500 'offset by 500
PULSOUT 14, time 'send pulse to servo

DEBUG HOME, DEC5 time 'display time value
LOOP

Well this is the code I have that lets the servo turn to its full capacity both ways. I need to limit it to -/+ 80 degrees and display that value to the screen. That is the part I am stuck on

annamaria

kwinn wrote: »

First thing to do is figure out the mechanical linkage. Then you need to determine the position. The simplest method to do that would be using the potentiometer as part of an RC circuit.

' {$STAMP BS2}
' {$PBASIC 2.5}

time VAR Word
PAUSE 1000

DO

HIGH 7
PAUSE 10
RCTIME 7,1, time
time= time */ 185 'scale by 0.724 x 256
time= time + 500 'offset by 500
PULSOUT 14, time 'send pulse to servo

DEBUG HOME, DEC5 time 'display time value
LOOP

Well this is the code I have that lets the servo turn to its full capacity both ways. I need to limit it to -/+ 80 degrees and display that value to the screen. That is the part I am stuck on

tomcrawford

Test variable time for values that exceed +/- 80 degrees (might need to experiment to determine what the values are). Limit time to the corresponding range.

   if time < [value_corresponding_to_-80_degrees then
       time = [value_ya_ya
       endif
'similarly test and limit time to value corresponding to + 80 degrees

OR: read carefully where they talk about calculating the multiplier (185) and adjust it.

kwinn

Modify the program so you can step through the entire range of pulse widths and output the pulse width and RC time value, and write down the angle.