Measuring Hall-Effect switch pulse frequency

Thread Starter

Diversitile

Joined Apr 10, 2015
9
So I have a Hall-effect switch type flow-meter that gives out short square wave pulses proportionally to the amount of flow, roughly 0 to 1000 pules per minute. I need to find a way to measure this frequency in order to get some data out of that flow-meter. I have seen similar projects involving Arduino, but I don't own one nor do I want to spend that much money. Is there a simple device that can count these pulses or perhaps some circuit that I can assemble?
 

dl324

Joined Mar 30, 2015
10,481
It's worth a try if you already have a meter that measures frequency, but success depends on what the meter considers "periodic" and the algorithm used.
 

Thread Starter

Diversitile

Joined Apr 10, 2015
9
I don't have one, but could try to borrow one.
By the way how hard would it be to hook it up to some kind of microcontroller + lcd ? Don't see other options...
 

Thread Starter

Diversitile

Joined Apr 10, 2015
9
Well it's a water flow meter and I need to compare some water pump flow rates. I have the hall sensor but I don't have the corresponding digital hand-held meter. DMM would be the easiest solution.
 

dl324

Joined Mar 30, 2015
10,481
Well it's a water flow meter and I need to compare some water pump flow rates.
Sounds like this is a manual operation. Change pump, check flow rate with Hall sensor. You could use a simple 3 decade counter; or a universal counter if you want an off the shelf solution.
 

alfacliff

Joined Dec 13, 2013
2,458
in the old days, when things were simple, I would say use an integrator circuit, chargng a cap through a resistor, a tachometer circuit. if you go with an arduino or similar, count from the start of one pulse to the strart of the next, it works better than counting pulses directly. a counter with a fixed pulse rate from the clock gated on and off by the incoming pulses, works much better at lower frequencies.
 

Thread Starter

Diversitile

Joined Apr 10, 2015
9
Should have been more precise. In the end I still need to get ~5% accurate flow rate number so I can get a curve of flow-rate according to pressure.
I don't think that a counter could do that.

I should probably also mention that I have basic knowledge of electronics, but can easily make a electronic circuit if I have a scheme.
 

alfacliff

Joined Dec 13, 2013
2,458
thats the reason for counting a fixed pulse train, it it is running at a fairly high rate, and your hall effect pulses are slow, you will get a higher count. for instance 10 pulses per second from the hall detector, gating a 1000 hz pulse on, then off at the next pulse giving you a count of 100. the arduino and others can be setup to give you the count pulses and to gate them with the incoming hall detector pulses.
 

Thread Starter

Diversitile

Joined Apr 10, 2015
9
I think I have come up with an easier solution.
What if I just use an old bicycle computer? Those work with reed switches, but I could modify the circuit to work with hall effect switch. Just add power supply to hall switch and connect output from it to the base of the transistor. That should emulate reed switch, atleast in my mind.
Will that work?
 

Reloadron

Joined Jan 15, 2015
5,338
The image you posted shows R1 as a pullup for an open collector output. In that scenario the pulses will be about 5 volt amplitude so if 5 volts is fine than things should be fine.

Ron
 

Alec_t

Joined Sep 17, 2013
11,130
R1 is a pull-up resistor so that the Hall output can switch between 5V and ground.
If you use the circuit as per post #14 then there will be no supply incompatability problem. If, on the other hand, you were to drive the computer directly from the Hall output and that output could pull up to 5V then there could be a problem if the bike computer supply were only 3V, say.
 

Thread Starter

Diversitile

Joined Apr 10, 2015
9
So I am putting things together and wondering how exactly do I calculate transistor's base resistance (R2)? Using circuit as per post #14, hall sensor supply 9V, bike's computer supply 3V and using BD139 transistor.
 
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