Control servo speed with Prop Pot

[tstamand]

Is it possible to manually control the speed of a servo with a Prop Pot connected to a Prop-1?

[JonnyMac]

Servos move at a given speed, so the only control you can do is hold the servo at intermediate positions when moving from point A to point B.  You have to be a tad careful, though, as the timing resolution on the BASIC Stamp 1 is somewhat coarse (one millisecond) and this can cause stepping in the movement.

Perhaps you're actually looking to control servo position with a potentiometer -- this is pretty easy and I've included a program below to show you how to do that.

' =========================================================================
'
'   File...... Servo_Pot.BS1
'   Purpose...
'   Author.... Jon Williams, EFX-TEK (www.efx-tek.com)
'   E-mail.... jwilliams@efx-tek.com
'              Copyright (c) 2008 EFX-TEK
'              Some Rights Reserved
'              see: http://creativecommons.org/licenses/by/3.0/us/
'   Started...
'   Updated...
'
'   {$STAMP BS1}
'   {$PBASIC 1.0}
'
' =========================================================================


' -----[ Program Description ]---------------------------------------------


' -----[ Revision History ]------------------------------------------------


' -----[ I/O Definitions ]-------------------------------------------------

SYMBOL  PosCtrl         = 7                     ' SETUP = out; no ULN
SYMBOL  Servo           = 0                     ' servo control pin


' -----[ Constants ]-------------------------------------------------------


' -----[ Variables ]-------------------------------------------------------

SYMBOL  position        = B2


' -----[ Initialization ]--------------------------------------------------

Reset:
  PINS = %00000000                              ' clear all outputs
  DIRS = %00000001                              ' make servo pin an output


' -----[ Program Code ]----------------------------------------------------

Main:
  POT PosCtrl, 104, position                    ' raw reading, 5 to 255

  ' convert raw pot value to 100 to 200 for servo (90 degrees)
  ' a) divide target span (100) by raw span (250)
  '    100 / 255 = 0.392
  '    -- convert for ** by multiplying by 65536
  ' b) apply [fractional] multiplier to raw span for scaling
  ' c) add minimum position value (100)

  position = position ** 25700                  ' convert to 0 to 100
  position = position + 100                     ' minimum CW value

  PULSOUT Servo, position                       ' update servo
  PAUSE 15

  GOTO Main


' -----[ Subroutines ]-----------------------------------------------------


' -------------------------------------------------------------------------


' -----[ User Data ]-------------------------------------------------------

[Raisin-Toe]

When using the Prop-1 Trainer, the P6 jumper is in DN position. But what about the P7 jumper?

[JonnyMac]

If using the POT circuit on the Prop-1 Trainer the SETUP jumper should be out, and the ULN2803 should have been changed to a ULN2003.  If using the P6 header on the trainer for your servo be sure you don't press the button on the Trainer as this will short the control signal to ground.