On Wed, 11 Nov 1998 15:33:03 +0100 Leonardo De Palo writes: >Hi PICer, > >I have the necessity to count object, using a 16F84. > >My idea is to use a couple of infrared diode and receiver (like the IR >used >on TV). That;'s a good way to start. The receivers are sensitive and have good rejection of ambient light. I don't know if these units like to receive a continuous carrier, or if they have AGC that will try to cancel it out. You may have to chop the transmitter on and off at a KHz or so in addition to the 40 KHz carrier. > >But, thinking at the environment of the installation site, it possible >that >some sunlight can arrive to the sensor, and I suppose that sunlight >can >saturate the receiver photodiode. Yes it can. You can tolerate some sunlight, but it will be very difficult to make it work if the sun shines directly into the receiver. > >I have the idea to try to minimize the effect of the undesidered light >with >some black plastic tube, but before to begin to build the prototipe, I >would >like know if exist a method to drive the LED to ignore o reduce the >sunlight >saturation effect. It is important to exclude strong light that can saturate the receiver. Lenses also work and have the advantage of collecting more light from the desired direction. But the key is to use modulation so that the receiver can tell if the light being received came from the transmitter or soemwhere else. An additional advantage can be gained in a stationary installation like this by synchronizing the transmitter and receiver. The receiver has a balanced demodulator driven by a copy of the transmitter's carrier. In some circles this is called a "lock-in amplifier". An old-timey 567 tone decoder chip can implement the entire system except for the LED driver and maybe the receiver preamp (though the 567 input is decently sensitive as it is). ___________________________________________________________________ You don't need to buy Internet access to use free Internet e-mail. Get completely free e-mail from Juno at http://www.juno.com/getjuno.html or call Juno at (800) 654-JUNO [654-5866]