Electronic Circuit Design Help Needed.

Discussion in 'The Projects Forum' started by R.Stephen, Mar 3, 2006.

  1. R.Stephen

    Thread Starter New Member

    Mar 3, 2006
    Electronic design assistance needed.
    I am seeking assistance from someone that would assist me in designing a custom circuit for a prototype that I am working on. I would be willing to work out a mutually lucrative contract with someone who wanted to get involved with this project. I will however require a confidentiality contract to be signed along with a specific contract, outlining both of our responsibilities and obligations. If this sounds interesting to you please contact me. Below is a “general” description of the circuit and the design objectives.

    General Circuit description: SEE ATTACHED!

    Circuit components: 1. Tank filled with liquid
    a. fluid hose to pump
    b. (FAULT) switch or Low level float consisting of a magnetic float incased around a tube with a no/nc reed switch.

    2. Liquid 12vdc @ 5a pump
    3. Trigger momentary switch to activate cycle.
    4. Reset Switch.

    Circuit requirements

    When momentary switch(3) closes for 2 seconds, pump(2) will activate (ON) for an adjustable time from 2-3 seconds. After pump(2) has activated an adjustable timed 10-60 minute countdown of the pump (off) will begin. Any additional signals from momentary switch(3)will not interrupt this cycle. If when cycle is complete a switch closure from momentary switch(3) still exists the cycle will repeat. If at any time circuit receives a signal (NC/NO) from fault switch(1-B) cycle will be immediately shut down and not restart until manual reset switch(4) is pressed.

    Notes: 3. Momentary switch to activate cycle could be in the form at current of an ultrasonic movement detector as seen here.
    I have not tested this switch yet to insure that it will perform the necessary detection capabilities, so this may change if a more suitable device is located.

    Notes:4 The reason for the manual reset button or circuit is that the float switch is very sensitive. The potential exists that when liquid level is low and pump activates, the amount of fluid that the pump draws to prime itself, may momentarily fool the float switch into thinking that tank has become empty. When pump shuts down and pump looses it’s prime a small amount of fluid will back flow from pump back into tank causing the level to fool the fault switch into thinking it has an acceptable level. I want to avoid a toggling effect that may be created when level gets into this level of liquid.

    General Notes: I have found several cyclic timers that could possibly perform the above list of requirements. They are listed here.
    Either of these circuits could work, with slight modifications, but they are not exactly what I am looking for.

    R. Stephen
  2. Papabravo


    Feb 24, 2006
    For a quick prototype, have you considered using a Programmable Logic Controller (PLC) from Allen-Bradley or similar vendors. They are readily available, easy to program, and widely supported. This application would be up and running long before you could design and fabricate or breadboard a custom design. Another advantage would be that if your requirements changed or you desired some new feature it could be added quickly and painlessly.

    Once you have a PLC design working the way you wanted, you could design a custom product to mimic the PLC solution.
  3. thingmaker3

    Retired Moderator

    May 16, 2005
    A couple of monostable multivibrators and some AND gates might do the trick. One MMV for the two-second window, one for the pump on-time, another for the 10-60 minute lockout.

    Another monostable and logic gate could eliminate the need for a reset switch - the "liquid level low" condition could be initiated only if the float switch remains tripped for ten or twelve seconds.


    This project reminds me of the self-administered morphine gizmo that my wife had when she was in the hospital. A hand-held switch triggered injection of morphine into her IV, but only one carefully measured dose in a specified time interval. She could press the button any time the pain got out of hand, but the machine would not let her overdose. I suspect the button had a bit of a "placebo effect" as well.

    I am curios... what does "mutually lucrative" mean?
  4. Starwalker9

    New Member

    Dec 4, 2006
    If you are still looking for someone I would be glad to get involved. I am currently designing circuits for television and music video special effects. I also design and manufacture circuits for the traffic and amusement industries. Dont be intimidated into thinking I charge top dollar! Just a regular guy who is always looking for work. Your controls could be handled easily with a $5 microcontroller. Email me if you are interested. I write firmware, design PCBs and manufacture if required.

  5. Gadget

    Distinguished Member

    Jan 10, 2006
    EZ PeeZee.