Sine to square wave converter

Thanks for reply Lord. Unfortunately link is dead!

Whoops, i'm sorry the link is working! Something was wrong here!

There are trivial ways to do it...it all depends on how "square" square must be. Do you absolutely HAVE to have 50.000% duty cycle, or are you only worried about using it as a leading (or falling) edge clock. Do you have any spare circuits in another multi-circuit chip, or do you have room for a dedicated chip. Tell us what matters to you and we'll have a shot at making the sucker go.

Jim

If a 50% duty cycle is important, a zero-cross detector into a D flip-flop as divide by 2 would get pretty close. GG

One simple way is to use a large value resistor, like 1MEG, into the base of an NPN transistor. The emitter should be grounded, and the collector tied to your +5V power supply rail through a 100k resistor. Take the output from the collector of the transistor. Note that for this to work, your power supply should have it's ground someplace near earth ground.

One problem with this is that the base goes very negative. This can be a problem. Thus, if you use a diode from ground to base, if the input goes very negative (which it will, of course) the diode will keep it within about 7/10 of a volt of the ground.

So

VCC | .-. | | 100k | | '-' | o------ PIC Input | 1MEG | ___ |/ AC IN -|___|----o----| | |>

| | - | ^ | | | | | GND ------------o------' (must be near neutral) (created by AACircuit v1.28.5 beta 02/06/05

This is probably going to be fast enough so that the PIC will only see one transition for each transition of the AC line. However, if it isn't, you can build a simple schmitt trigger out of two transistor that will prevent false triggering.

That would be like this (which is swiped out of Art of Electronics, Volume 2)

.--------------o--------- VCC | | .-. .-. | | 1.5k | |1k | | | | '-' '-' | ___ | o---|___|--. o------Output to PIC | 10k | | 1MEG | | | ___ |/ | |/ AC IN -|___|----o----| '-| | |> |>

| | | - '------o-------' ^ | | 100R | | ___ | GND ------------o----|___|----' (must be near neutral)

(created by AACircuit v1.28.5 beta 02/06/05

However, I think the first circuit is probably ok.

This will explain how you should proceed:

I read in sci.electronics.design that Jack// ani wrote (in ) about 'Sine to square wave converter', on Thu, 24 Mar 2005:

IE6 barfs badly, but Firefox retrieves it OK. I'm having the same problem with PDFs from other sites, using IE 6 and Acrobat 6.

All depends on what you're trying to do. If all you need is line synchronization... On PIC16F877A, I've used a voltage divider directly into the input. The inputs are clamped. As long as you have enough series resistance to limit the current, it should work ok. External clamps are even safer. Transistor is better. You can spend as much as you like. Use SW to mitigate noise. Assume you have mains isolation. mike

Works fine for me.

Graham

It depends on what powers your logic circuit and what it needs the 50Hz square wave for. You can't just couple a voltage off the line into a GND referenced circuit and expect it to work trouble free. Also, most circuits are looking for zero-crossing on the AC- waveform and this is difficult to get with the massive attenuation required of a line voltage in conjunction with the fairly large uncertainties of typical Schmitt trigger thresholds and hysteresis. You will get a square wave, but it may not be of much use.