Looking for advise on PC FlowMeter

Nice but you will have to have a way to multiply the paddle wheel pulses into the KHz range. Most system fans want about 3500 RPM to prevent a 'fan to slow' alarm. I am assuming that one revolution of the fan results in one pulse on the tach, you'll have to test that theory. Perhaps a phase locked loop (PLL) with a divider in the feedback path will do. Look at the spec sheet for a 4046 here:

Don Lancaster has a section in his 'CMOS Cookbook' regarding this device. Don's web site is

I'm guessing that there is a pump motor in this cooling system, what about stealing a tach signal from there?

How about a temperature to frequency circuit?

Thanks for the ideas, much appreciated. I could and probably will set it up with 3 or 4 magnets, so it'l be that many pulses per rev. It will have to have at least two just to keep the paddle balanced. The software I'll be using is very flexible, and the fan speed alarm do not have to be used.

I'll check it out, thanks.

This won't help me if a line gets plugged, the pump goes ntts, or something stupid like that. Also, I'm interested in seeing just a simple drop in flow rate as opposed to waiting for a complete stoppage if something bites it.

I'd rather not wait for the temp to go up, by then it may be too late.

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You should start drinking prune juice and KY jelly cocktails right now, that will make things a lot smoother. -Felatio Love

You could make it dead simple. Mount a reed switch where it's actuated by your paddle wheel magnets. Ground one side of the reed switch, connect the other side of the switch to your input pin, with 4K7 pullup to +5V. Maybe a 1 nf cap across the switch, just because you can. (try it with and without a cap, and see if it affects your debounce code).

Debounce it in software - you've got all day to do that, practically. :-)

Have Fun! Rich

You could recover the hall effect sensor from an old fan and use it directly as there would be no contact bounce. Many newer fans contain an IC that includes the coil drive transistors and the 4 or so passives that the old style needed. I have yet to investigate these for potential reuse.

If the cooling system plugs up and the heat rises, the motherboards should already take care of this situation by slowing or shutting down besides, the temperature rise is a simple scaling operation ... how much temp to tolerate before it is a problem.

For the plumbing to stop up, assuming the pump continues to run, you could use a change in fluid level within a bottle to detect this situation.

Another approach would be to skip the moving parts completely, and just hang a transistor or diode junction in the flow path. Apply a small current to get it to self heat, and measure the voltage drop across the junction. This is linearly proportional to temperature, so you can thus determine how much cooling is taking place. There are all sorts of schemes based around this concept, often involving a second such sensor in a bridge arrangement. It's commonly used for airspeed measurement. You may want to look up "hot wire anemometer", since this was originally done with resistance wire instead of junctions.

Best regards,

Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis

directly

These sensors or in every fan as their purpose is to replace the mechanical commutator. A typical third wire tach fan simply outputs one of the coil pulses. That's why you should not pay a big premium for this 'cheap to include' feature.

I have one fan that has a stall sensor built in. I suppose the output is constantly reset by a moving fan. In any case, you get a signal if the fan stops.