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I need help with a prototype design

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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

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


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    555 ic's have been around for a long time the 555 ic only cost about 30 to 50 cents , depends on were you buy it. Cheep but it dosen't have brains. A mcu dose, I don't think you want to go with that, Willian is right about using a Pic mcu for what you wnat a 14 pin pic could very eaisly controll the sensors for around a $1.25 a chip. Pluss it would let you have input to the process which would give you a lot of options to add to your project.

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In reference to your question regarding the pump.
The pump does not need to reverse it's polarity. It only needs to be activated then delayed thru a complete cycle. I have looked at a few commercially available timer circuits. The one thing that I don't want is for the circuit to reset until cycle has completed. Several timers appear that when the trigger is activated again in mid cycle the circuit starts over. Not desiarable!
R. Stephen

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