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What I'd like to do is modify the circuit to give out rpm speeds to be connected to a fan header.
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i had logical circuits 7 years ago
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but i think the circuit doesnt work as you think.
My reading of it (looking at the circuit) is that there's a timer circuit with a variable step (monostable) that maintains a down (or high, can work both ways) signal as long as the capacitor doesn't discharge completly. When you ajust the potentiometer , it ajusts the step. What happens is if the flow drops, the time between bursts from the hall sensor becomes larger than the time needed for the step to remain down, and it goes up, and it changes state on the flip-flop, just like a shmitt trigger circuit (i think). However it must have a small histerisis or it would be going on/off all the time on the designated setpoint.
Anyway, if you have the sensor itself, you can build a circuit to read the hall signal, there's a few circuits out there, you don't actually need the flowswitch circuit. Try searching for hall effect circuits (and reading).
I don't know any, but i'll see if i can find out.
In last resort, try using a fan circuit, they have a hall sensor and they already have a tach output -> desolder the hall from the fan, connect wires from flowsensor. But be careful because of voltage considerations, i dont know if they are interchangeable.
(remember this?
http://www.overclockers.com/tips642/ )
I could be wrong.
