need help debugging the circuit!

Thread Starter


Joined Jun 18, 2009
I started a project in electronics and I done everything in it but still a problem crept in n the circuit is not working. I need help in this regard!

The project is KnockLock. Its aim is to detect knocks on the door and determine if they are in correct pattern or not and to Lock or open the door based on the knock pattern detected. I got the design onto PCB. Microcontroller is flashed with program and ready. Somewhere there is a problem I am unable to diagnose. Please help! I am attaching a schematic of the circuit I made. The circuit should wait for a knock, detect asap its done n work accordingly. But the circuit on PCB is detecting a invalid knock as soon as the electet microphone is powered up and is never returning back from that state. The knock pattern should be waited for after 8 sec from detection of a invalid knock. But No, It shows invalid knock, Just in its way! Thanks if u can bail me out!



Joined Aug 15, 2007
Look at the signal going into the micro (PDk). Then review your transistor theory.
(1) How does PDk get a signal? -- that is, what happens when VB > VE?
(2) How much greater than VE must VB be? How ans when does this occur?

Hint: I've never seen an NPN transistor's collector connected to ground.*

* Not that it can not be done, it's just that I have never seen it.