# Voltage comparator circuit

Discussion in 'The Projects Forum' started by javajoe, Mar 29, 2011.

1. ### javajoe Thread Starter New Member

Mar 29, 2011
3
0
I have a project that involves using a simple DC circuit that will test for three voltage ranges and turn on three different LED's within each range. For example: Red LED would turn on when Vin drops below 5Vdc, Green LED would turn on with Vin in the range 5Vdc to 6.9Vdc, and Amber LED would turn on with Vin at or above 7.0 Vdc. I have 12 Vdc also coming in that could be used as a reference voltage which can be divided to give 3 ref. voltages. I also have an OP amp(339) to use as the comparator. It would be nice if each LED would lite up independently when in each range. So I'm looking for the green LED to lite up at that 5 to 6.9 Vdc range and turn off if the other voltages are encountered either High or Low. A circuit diagram would be helpful for me to get my brain around this problem.
Thanks

2. ### CDRIVE AAC Fanatic!

Jul 1, 2008
2,223
103
You won't be able to fulfill your requirements with one OpAmp or Comparator. Here's the easy way using a uC.

File size:
33.4 KB
Views:
44
3. ### javajoe Thread Starter New Member

Mar 29, 2011
3
0
Won't this circuit work?

File size:
148 KB
Views:
52
4. ### Wendy Moderator

Mar 24, 2008
21,351
2,918
A quad comparitor should be able to do it I would think. Basically one for low, one for high, and a diode OR gate for when both outputs are low. 3 comparitors,several diodes and resistors.

5. ### shortbus AAC Fanatic!

Sep 30, 2009
5,566
3,179
You were one click away On the PDF you posted near the bottom it says "related circuits" one of them takes you to this; http://www.aldinc.com/pdf/cd_23001.0.pdf

Now, its for a four way comparator circuit, but if you just eliminate one of them you will have your three way comparator

javajoe likes this.
6. ### javajoe Thread Starter New Member

Mar 29, 2011
3
0
Thanks for that info I'll try this and let you know of the results.

7. ### shortbus AAC Fanatic!

Sep 30, 2009
5,566
3,179
If you use that circuit for only three of the four comparators you should ground the unused input pins, the unused out put can/should be left floating.