555 servo needs a reset set position?

Discussion in 'The Projects Forum' started by stanman11, Nov 23, 2010.

  1. stanman11

    Thread Starter Member

    Nov 23, 2010
    Hi im new and will make this quik. im holding my baby and typing

    i have a pulse circuit 555 timer to a servo using no potentiometer and only a 1uf capasitor and it turns forward but i need it to turn back or reset after it turns.

    i dont have a programmer but i do have some oth IC's but not sure if they will work.

    im trying to open a valve then have it turn back autmagicly to shut off

    how can i do this on a 555 ic timer?

    oh also i need to controll 2 different servos using one 555. i can figure that out but not the servo return
  2. retched

    AAC Fanatic!

    Dec 5, 2009
    You must get the pulse that is required for the reverse action from the datasheet for the servos.

    You may need to incorporate another 555 to make a complex pulse. For instancee, a single pulse every 10 mS will operate the servo or actuator to open. But a double pulse every 10 mS will reset the servo to the start position.

    Do you have the servo information? Manufacturer, model #? A link to the datasheet would be most helpful in solving this.
  3. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    If it is a modern hobby servo, a pulse of >1.5 mS every 20 mS will move one direction and a pulse of <1.5 mS every 20 mS will move the other direction. The repeat rate (i.e., every 20 mS) is not critical, but the duration of the pulse is. The center width (1.5 mS) varies a little from servo to servo.

    You only need one 555 and a pot to control such a servo.

  4. hgmjr


    Jan 28, 2005
    Something like this is what jpanhalt is recommending.

  5. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    I think that link is what the OP has, but is looking for a "Return to Center" switch without moving the potentiometer, though I'm not quite sure.
  6. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    I was thinking that the OP was using a fixed timing resistor (i.e., "no potentiometer") in one of the circuits like hgmjr's link. To make it go back and forth could be as simple as using two resistors and a switch.

    If the OP would post his circuit, we could even give a pretty good guess for the resistors to use.

  7. retched

    AAC Fanatic!

    Dec 5, 2009
    I was thinking about how good tomorrows dinner is going to be ;)

    Actually he says he is using NO resistor, just a 1uf cap for timing.

    So, he may have an actuator instead of a servo, per se.

    It doesn't seem to have spring assisted return, so it will require a particular signal to return.

    These are used in HVAC on valves all the time. If a room hits proper temperature, the analog thermostat will change the resistance between 2 of 3 wires.

    If the resistance between white and red are greater, the hot water valves open

    If the resistance between white and blue are greater than white and red, the valves close.

    Digital versions use a pulsed signal. A particular pulse will turn the device to a particular angle.

    A different signal will return it to "reset" or "starting" position.

    It depends on the setup.