Here is what I have right now:
**broken link removed**
At the very top, I've got a LM7805 regulator to regulate the voltage from 12V to 5V. Let me describe this a little more thorough:
Before adding the 5V regulator, I originally had a plain 5V source connecting to R7. The active HIGH circuit that I added is circled in red. If the voltage at "KNOCK INPUT TO MS" is 0V, the voltage at "KNOCK OUTPUT TO MS" is 5V. If the voltage at "KNOCK INPUT TO MS" is 12V, the voltage at "KNOCK OUTPUT TO MS" is 0V. Now, before adding the 5V regulator circuit (in green), this functioned perfectly. Since it wouldn't be very practical to have both a 12V and 5V input to the board, I decided to use the regulator from the 12V source and regulate it to 5V.
In my mind, I don't see where i went wrong. I simulated the circuit with a basic 5V source and it operated just as it is supposed to. Now that I added the 5V regulator, when SW1 is open, my "KNOCK OUTPUT TO MS" is 5V just like it should be. When I close the switch, the voltage goes down to 20mV instead of 0V. If I open the switch, the output is supposed to rise back up to 5V, but with the regulator in the circuit, it doesn't. It still stays at 20mV. After a few seconds of simulating it with SW1 closed, the simulation will fail and Multisim reports and error log that I can't understand.
Can anyone tell me why the 5V regulator is cause this to crash and function improperly?