I'm building a circuit to detect when a laserpointer's beam has been broken. Im using a photocell, 741op amp, and a relay in the circuit. I have a small buzzer on a NC contact of the relay, so when the beam is broke, it buzzes. Now it works fine right when i turn it on, and i can break the beam and the buzzer sounds. But if i leave the laser on the photocell for a minute or so, when i break the beam, the buzzer starts up, and keeps going despite the beam being back on the photocell. Any input would be awesome. thanks