Square wave to DC convertor

asjad · Posted: Thu Apr 15, 2004 2:14 am

Dear All,

Does anyone know how to convert a square wave into a DC signal

I have hgeard you can use a low pass filter OR a diode and a filter.

Ccan anyone help.

I need compnenet values or weblinks please!

Thank you

Asjad
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Best Regards

Ttelmah · Guest

asjad · Posted: Thu Apr 15, 2004 2:55 am

Unfortunatly I do not know the frequency that will be coming out at this
stage.

THe output will be derived from a liquid flow meter.(output=pulses).

I wish that if a liquid is flowing I get a logic 1.
If no liquid flows I get a logic 0.

I will be using a 16f874's external interrupt

will this circuit do:

http://www.callerid.8m.com/mini/peakdet.htm

I am not sure how it works though
-------------------------------------------------------------

FOr your original soloution proposal can you PLEASE
give me a formula to calculate R & C and the configuration!!

Best Regards

Asjad
_________________
Best Regards

Humberto · Posted: Thu Apr 15, 2004 6:48 am

Hi asjad,

It will be easy & cheaper to do it using a rettriggerable monoestable multivibrator like the 74HC4538 or similar.
Configure the setup pins as retriggerable monoestable, feed the trigger input with the pulses coming from the flow meter and choosing the Q output you will get a stable HIGH state while the pulses kick the trigger input.

Exclamation

Connect to GND all unusued inputs

Regards,

Humberto

Ttelmah · Guest

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

The peak detector circuit with an op amp, or the missing pulse detector with the 555 are more accurate and more expensive than the diode + RC circuit I mentioned in an earlier post. It all depends on what accuracy you need.
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dbotkin · Joined: 08 Sep 2003 Posts: 197 Location: Omaha NE USA

I dunno... you could do this with a monostable, but why bother adding parts? Just watch the flow meter output with one of your inputs. Use a short variable to indicate whether it's gone high within the last whatever period of time you want. I can think of several ways to do it, like using an interrupt-on-change, or a CCP input in capture mode, or if the pulses are long enough check it during an existing (or new) timer-driven ISR. Now you have the flexibility to change the time constant of your software "one-shot" to whatever you wish without having to change components.

If a picture is worth a thousand words, a few lines of code can be worth a few dozen solder joints. Make sense?