Help with LM393 Voltage Comparator Required

Hi,

I need to use this chip in a much larger circuit, but first I need to get a handle on it. I can't seem to get it to work properly.

When I turn the variable resistor, I either get 0.5V or 0V on the output pin. This isn't enough to light the LED. I was expecting 5V or 0V. Have I wired it up wrong? Are my resistor values off? Any suggestions would be greatly appreciated.

**broken link removed**

I got my problem solved. My error is too stupid to mention. lol

micro571 said:

I got my problem solved. My error is too stupid to mention. lol

Click to expand...

Humor us :wink:
Open collector outputs can be a pain :lol:

I copied the circuit diagram and changed it a bit to what I actually had.

Then I realized that the LED in the diagram had the negative side going into the output. I flipped around my LED and it worked. Oops.

When I was measuring voltage, I was measuring from output to ground, which would explain the low voltages.

My bad.

micro571 said:

When I was measuring voltage, I was measuring from output to ground, which would explain the low voltages.

Click to expand...

No, it has an open collector output, wich means it can only pull the output to ground, it can't put '+' on it. That's why you read those low voltages, It needs a pullup resistor on the output...

yup open collector. You really need a the LED-330 Ohm going from the 5V rail and the comparator output