L14G3 phototransistor and a continuous rotation servo

Mike W

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I have started experimenting with a L14G3 phototransistor and a continuous rotation servo. The object was that when the transistor sees light it would turn the servo. I programmed the SX/B with the code below, and wired the transistor as shown in the diagram. The project works as I expected with one exception.
My problem is if I touch the 220 ohm resistor between the transistor emitter and the SX pin RC.0 the servo will turn, can anyone explain this to me and help me fix this problem.


Right:
· PULSOUT RA.2, 149, 1······························ ‘ pulse out to servo on RA.2
· PAUSE 20
· RC.0 = 0
· GOTO Main
'

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' Program Code
'

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Start:
· INPUT RC.0················································ ‘ input from phototransistor
Main:
· IF RC.0 = 1 THEN Right
· GOTO Start



Post Edited By Moderator (Chris Savage (Parallax)) : 4/22/2005 5:53:28 AM GMT

Bean

You should have a pull-down resistor, from the emitter to ground.
When the transistor is off, the input is floating (bad).
Try a 10K then move up or down from there.
Bean.

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Mike W

Thank You Bean!

The 10K resistor did the trick I appreciate the help.

Mike W