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Servo on separate power source — Parallax Forums

Servo on separate power source

p_tp_t Posts: 15
edited 2013-02-18 16:03 in BASIC Stamp
I Found an issue using the 16 serial LCD and a continuos servo at the same time and decided to just use a separate power source for the servo so that it doesn't affect the LCD. I used a 7805 +5V voltage regulator and used a .33 and .1 micro farad ceramic capacitors as filters. I am using a 9 volt battery. Now the servo does not follow the the clockwise and counterclockwise rotations using the following code. It only rotates in a clockwise rotation. I thought maybe I would have to zero the servo again on the new power source, however it did not let me zero it, it only continued to go clockwise. I added another pot to see if that would make the correction but it didn't help. Any help on this situation? I also tried to use the LCD on my separate power source but it would not work at all.

servo PIN 14
counter VAR Word


DO
FOR counter = 1 TO 10
PULSOUT Servo, 850
PAUSE 20
NEXT
PAUSE 500
FOR counter = 1 TO 10
PULSOUT Servo, 650
PAUSE 20


NEXT
LOOP

Comments

  • pogerttpogertt Posts: 33
    edited 2013-02-18 15:00
    Do you have the common or negative on both power supplies tied together?
  • Mike GreenMike Green Posts: 23,101
    edited 2013-02-18 15:01
    Servo motors draw much more current than you might think (up to 1A when starting or with a heavy load) and 9V batteries have much less capacity than you think. Use a 7.5V to 9V "wall wart" AC input power supply that's rated for at least 1A.

    You may want to make the FOR loops longer. With a 1 to 10 range, the motors are activated for only 200ms ... not much time. Try at least a 1 to 50 range. That's 1/2 second of movement each.
  • p_tp_t Posts: 15
    edited 2013-02-18 15:13
    pogertt wrote: »
    Do you have the common or negative on both power supplies tied together?

    No, the only thing linking the servo to the stamp is through the pin.
  • Duane DegnDuane Degn Posts: 10,588
    edited 2013-02-18 15:15
    This recent thread might help.

    As Mike suggests, a 9V battery isn't a good power supply for a servo.
  • pogerttpogertt Posts: 33
    edited 2013-02-18 15:24
    If you connect + and - to the servo with out providing it with a positioning pulse, it will drive itself to one end of it's travel.

    If the ground, negative, or common terminals are isolated from each other, then there is no path for current to flow in the pulse portion of your circuit.


    You might want to try to connect both negatives together, and follow Mike's advice about the power supply versus a battery.
  • p_tp_t Posts: 15
    edited 2013-02-18 16:03
    pogertt wrote: »
    If you connect + and - to the servo with out providing it with a positioning pulse, it will drive itself to one end of it's travel.

    If the ground, negative, or common terminals are isolated from each other, then there is no path for current to flow in the pulse portion of your circuit.


    You might want to try to connect both negatives together, and follow Mike's advice about the power supply versus a battery.

    Success! Thank you Pogertt. Also thank you again Mike, I will get myself a plug in, batteries are starting to get expensive anyways :)
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