Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Actuator-solenoid valve circuit

  1. Dec 5, 2011 #1
    So I designed a circuit. It is controlling a pulsating actuator-solenoid. I used a power BJT as shown in attachment.

    Now I have a problem.

    As you can see all 4 circuits are in parallel. As a consequence, all 4 solenoids have one lead in common.

    When I test each subcircuit, it works fine. You can see in the attachment a picture of my circuit. Left 8 leads are going to potentiometers. Each potentiometer is controlling one solenoid. As I said, when only one solenoid is connected it works fine, I can adjust the speed of pulses as I desire.

    But when I put all 4 solenoids, and turn on the circuit something bizarre happens. If they are all at the same frequency, ergo all pots are at same level, they pulsate ok. But when I change one of the solenoids frequency, it shuts off(that solenoid). Others stay the same, but of course other 3 are at the same frequency. It doesn't pulsate slower nor faster.

    As if my circuit does not withstand multiple frequencies.

    Am I making some obvious mistake?

    Can this circuit be modified, or are there any other circuits for this mechanism to work?

    Idea is to control the flow of water. Valve opens and shuts and that controls how much water is sprinkling. Those pots are controlling the speed of those impulses.

    I used 555 timer to do this.

    Attached Files:

  2. jcsd
  3. Dec 5, 2011 #2


    User Avatar
    Science Advisor
    Gold Member

    Could it be that you need a diode across the coils?

    http://www.kpsec.freeuk.com/images/diopro.gif [Broken]
    Last edited by a moderator: May 5, 2017
  4. Dec 5, 2011 #3


    User Avatar
    Science Advisor
    Homework Helper

    You should have the protection diodes in #2 regardless of your problem.

    When one timer switches, the relay may be putting a voltage glitch into the power supply lines that is triggering the other timers with a similar time constant, and/or resetting the "odd one out" so it never manages to trigger.

    Try your circuit with the "odd one" triggering both faster and slower than the other three. That might prove the point.

    I would have separate the "analog" and "digital" power supplies. Make a simple smoothed power supply for the timer chips, that takes power from the 24V supply and delivers a lower regulated voltage to the timers. E.g. a 7815 regulator chip, or even a zener diode regulator. Use that to power the top end of R3, R8, etc.
  5. Dec 6, 2011 #4

    jim hardy

    User Avatar
    Science Advisor
    Gold Member
    2018 Award

    i'd wager your power supply is 'collapsing' under load of multiple solenoids.

    first try a really stout supply like a car battery

    and with 555's, power supply bypassing is important especially if leads are long.

    try a couple thousand uf real close to the 555's, and a 0.1 ceramic even closer.

    that should change symptoms, at least.

    hands on is way to learn. keep it up!!!
  6. Dec 6, 2011 #5
    Omg it looks so obvious!! How could have I missed that?!!? Signals are in deed mixing up.

    Power supply isn't the problem mr. jim. I was given 300 Euro, industrial 24V power supply, used in many machines today. It is giving out 24V all the time.
    Yes, these guys really trust me.

    One more question though. In addition of putting a diode in parallel, should I try putting a diode in series too?

    To ensure I am getting one way signal?

    To emphasize, my circuit has frequencies from 1Hz to 20Hz.

    About that capacitor, I put 10 uf in parallel with 555 timer. Like in the picture below. Is that what you are talking about?

    http://pokit.org/get/e212cc400b6d6f4eddcc49bc17d7e2cd.jpg [Broken]
    Last edited by a moderator: May 5, 2017
  7. Dec 6, 2011 #6
    To add: I soldered in series a 1N4148 diode and in parallel. I hope it will withstand pulses of 200 mA, datasheet says it will...
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook