I have a circuit here which was designed by others. It takes a 32.768 kHz IR input and outputs a logic low when the input is present. I see 3 distinct stages… everything up to U1A, everything between U1A and Q3 and everything to the right of Q3. I follow the left and the right… but not the center which is where all the magic happens.
The circuit actually works. I've wired it up and can verify that this does indeed work.
Can anyone explain the piece in the middle? It makes no sense to me. How is this circuit functioning? Why do they make use of all the gates? Why do they have a resistor in series with Vcc on U1? What purpose does R26 serve?