# "Is voltage equal to" curcuit

Discussion in 'The Projects Forum' started by bok, Jan 11, 2016.

1. ### bok Thread Starter New Member

May 7, 2010
2
0
Hi.

I have a signal that ranges between 0 and 5 volt, and i need to design a curcuit that outputs a logic 1 if this voltage is equal to 2.4V.
The tolerance is +-0.5 volt.

I been trying to crack this for a while, but cant seem to figure it out, anyone got any idea ow to accomplish this?

Bok

2. ### GopherT AAC Fanatic!

Nov 23, 2012
5,991
3,738

Google "comparitor" or "window comparitor" if the lower value is also important. That is, if you also want a logic 1 if voltage is below 1.9V (not in your 2.4V range).

Also, you may want to discuss/post schematics if what you've tried and failed with so far.

bok likes this.
3. ### bok Thread Starter New Member

May 7, 2010
2
0
Perfekt! The window comparitor is exactly what i am looking for.

4. ### MikeML AAC Fanatic!

Oct 2, 2009
5,450
1,066
Or a single comparitor with hysteresis, sometimes called a Schmitt Trigger.

For example, output become 1 when input exceeds 2.45V but the input has to decrease below 2.35V for the output to go back to 0. Such a comparitor would have a hysteresis of (2.45-2.35) = 100mV.

Here is an example. The Reference voltage can be derived with a voltage divider from V(dd). It requires an OpAmp or Comparitor chip that has a full-swing output of 0V to V(dd).

Last edited: Jan 11, 2016