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Connecting pulse output to Piezo alarm

Connecting pulse output to Piezo alarm

Connecting pulse output to Piezo alarm

Dear all,

I am mechanical engineer with no background to circuitry and electronics. I am trying to connect a flow switch ( using hall effect ,12 dc input) and I want it to trigger a piezo alarm (12V dc) when water flow stops.

There are three wires from the flow switch, two for power and one for signal out. the signal out is pulse signal based on the flow. I need to know how to connect this pulse signal to piezo alarm so that alarm goes off when there is no flow.

Any help would be much appreciated.


RE: Connecting pulse output to Piezo alarm

There are two problems with your request that require much more detail:
Quote: "the signal out is pulse signal based on the flow"

1) You have not given details of the piezo 'alarm' as to whether this is just a simple sounder or something more sophisticated that can be programmed.
2) You don't say what sort of pulse rate the flow switch produces or what sort of signal it is.

If the alarm is a simple sounder, the first thing to decide is what the longest interval between pulses from your flow switch will be before you consider the flow to be stopped. You will then need some sort of a 'hold up' and interface circuit which can drive the sounder. This will provide a time delay which is reset by each pulse and is just longer than the slowest pulse interval. This will time out after a delay and energise the alarm sounder.

RE: Connecting pulse output to Piezo alarm

Hmm, I don't know if there's a simple solution. You might be able to find a solution off the shelf, otherwise you (or your friendly local elec dude) will need to design one. US Patent 4845379A concerns just that and includes a handy schematic (for "inspiration"). Or you could use the pulse train to charge a simple RC circuit and use two comparators that detect the cap voltage going too far above or below some threshold. But in any case, it will be sensitive to the details of the pulse train that your flow "switch" generates.

It occurs to me that an easier solution might be to find a more suitable flow switch. The device you describe sounds more like a flow meter, which makes it a bit harder.

RE: Connecting pulse output to Piezo alarm

Google: missing pulse detector

Hopefully you'll find a simple 555 Timer based circuit. You'll still need to interface the input (hopefully you'll find that to be straightforward) and the output (definitely straightforward).

Of course, these days you could also, very cost effectively, program an Arduino or whatever uC you like, to perform the same sort of function; and with more bells and whistles. But you'd still need to interface the I/O.

RE: Connecting pulse output to Piezo alarm

It sounds like you have a flow-meter, not a flow-switch. A flow meter puts out a pulse rate proportional to flow rate. If you are not interested in the flow rate then use a flow-switch which is a paddle in the pipe that is pushed by the flow to activate a switch. The switch is on or off depending on the flow being on or off.
An electronic time-out between pulses will also work with your flow-meter, or you can use an actual flow-switch in addition to your flow switch.

RE: Connecting pulse output to Piezo alarm

Your pulse output won't drive much load. It's typically connected to a transducer that converts it to an analog (4-20 mA, 0-10V, etc...). Some "smarter" transducers have a switch output with an adjustable setpoint. Ask the folks you got your paddlewheel device from, they'll either have a transducer of their own or else they'll know of one.

I could suggest some, but I don't know the make and model of your flow device.

Best to you,

Goober Dave

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RE: Connecting pulse output to Piezo alarm

If I'm reading the specs correctly, interfacing might be 'connect-the-dots' simple. Good luck.

RE: Connecting pulse output to Piezo alarm

Arduino should be able to handle what you are trying to do. They are about $30 US at radio shack.

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