Flow sensor

Roger · Guest

Dear All,

I need help!!

I need to interface a liquid flow sensor to a PIC interrupt.

BUT the sensor gives a train of square wave pulses.

I do not want to measure them just need to know that some liquid is flowing

Can anyone suggest a circuit, Low pass filter???

Best Regards,

Roger

dyeatman · Joined: 06 Sep 2003 Posts: 1912 Location: Norman, OK

You didn't say which PIC you were using or the voltage range of the square wave. You could, for example, simply tie a 5V square wave signal directly to pin RB0 and set it for L to H Interrupt trigger. Depending on impedence you need to include a resistor (330 ohms for example) between the two just for protection of the PIC input.

If the square wave signal is more than 5V a two resistor voltage divider can be used to get it within the 5V range and then you wouldn't need to use the protection resistor.

Roger · Guest

PIC16f874

I am sorry if I confused you.

I only want there to be an interrupt IF the pulse train stop!!! (USING BO)

Regards

Neutone · Joined: 08 Sep 2003 Posts: 839 Location: Houston

dyeatman · Joined: 06 Sep 2003 Posts: 1912 Location: Norman, OK

To expand some on what Neutone said....

How fast do the pulses occur?

Example:
If they are twice per second then start a 700ms (something more than 500ms) timer at the first interrupt. Reset the timer every time a new edge comes in. If 700ms passes without an edge, the timer times out, a timer interrupt will occur and you can react.

SherpaDoug · Joined: 07 Sep 2003 Posts: 1640 Location: Cape Cod Mass USA