Electronic – Flipping Output Logic

comparatoropto-isolatorvoltage divider

I have the following circuit:

schematic
(source: siteonlinetest.com)

The diagram above has a pot between VCC, LM393 and Ground, on my board pictured below this is replaced by a voltage divider with two 10k pots.

It looks like this: (Front)

photo

The logic is currently as follows:

  • VCC=5v
  • Output=5v (obstructed), floating (open).

I need to flip the output logic and haven't had much luck in doing this. This board is the perfect form factor for my application and I would like to keep it if possible. Is there something simple I can add to it to accomplish this?

Best Answer

If you have access to a soldering iron with a very fine tip, and some very fine solder and wire (say, 30 ga):

1 - desolder pins 2 and 3 of the comparator

2 - bend the pins up as far as you can without breaking them (the tip of an xacto knife will work)

3 - using the fine wire, swap the pins' connections to the pc board pads

4 - use a drop of 5-minute epoxy to insulate the pins and jumper wires.

This will reverse the logic of your output.

Be careful not to leave any solder bridges.