The Circuit:
http://j3eglobal.multiply.com/photos/hi-res/1M/6I had a problem before in dealing with sensing or detecting a laser light. I made a counter project to count the number of persons entering a certain premise. The idea is to install from an entrance a laser transmitter and beamed opposite to the laser sensor. The count commences whenever a laser light is cut by a passerby. I successfully constructed the counter circuit.When i installed the prototype,i discovered a problem: counting jumps randomly. I suspected it is caused by the harmonic responses or glitches of the laser detector from the laser light.
I solved this problem by doing several trial and errors. Finally, the circuit i designed above solved the problem. The circuit consist of Photo-detector (in Photo-conductive configuration), the transistor driver and the one-shot multivibrator circuit.
The work of the Photo-detector circuit is to detect the laser light and reacts when there is an absence of light. When laser is cut, the transistor driver toggles from normally HIGH to momentarily LOW states. This triggers pin 2 of the 555 timer IC that produces an output of ONE-SHOT HIGH logic pulse. The LOGIC HIGH output can be determine by T=1.1RC. This output is sent to Clock In of the Counter...Every HIGHs or Pulse at the clock in, the Counter Counts...
This circuit works very well....I designed this last Oct132006... Any Q message me......
