0.5Vrms Sine Wave to TTL / 5v Square Wave

Thread Starter


Joined Mar 21, 2011

Firstly I have to say that I have basic knowledge about electronic (I'm studding Computer engineering) I know what is and how to use many logic circuits, resistors, capacitors, etc...

Well my problem is that I have a 1Hz 0.5Vrms sine wave and I need convert it into a 5v square wave (TTL). I saw many documentation online and I took some ideas but the main problem is converting 0.5Vrms into 5V.

I think that the sine to square can be done with a Schmitt trigger but I think that I need to amplify the sine signal first.

Any hint?



Joined Oct 22, 2008
Use a comparator, an op amp optimized for this exact purpose. An LM311 is an older comparator that I've used a number of times with good success. It will switch on millivolt signal levels and can be designed to give a TTL output (the output is open-collector).

Ron H

Joined Apr 14, 2005
LM393 is a cheap dual comparator. LM311 is a single comparator with higher sink current capability, which is good if you want to drive an LED or a relay. LM393 is fine if you just need logic level conversion.
This circuit has about 24mV hysteresis, to prevent multiple output transitions when the input crosses zero.
If you don't use the other comparator in the package, connect both of its inputs to ground.

EDIT: As L. Chung pointed out below, the input capacitor polarity needs to be swapped.


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Thread Starter


Joined Mar 21, 2011
Thx for all the info. I'm reading about comparators and how to use it. Let's see if I don't burn out them :)