I've seen the designs using the 555 timer as the base and making a 2 led IR emitter. These examples use 5v and only two leds to send the 40k signal. http://www.reconnsworld.com/ir_ultrasonic_555timer40khzir.html I would like to modify this design to run off 12v and use 8 infrared leds. I building a lap counter, I searched the forums and haven't found anything helpful yet. My idea was to build a bridge across the track and have leds space 1.5 inches across pointing down at the track surface, the bridge may be up to 20 foot wide, I am building it in removable 4 foot sections. My idea was to put the counters on the cars themselves and use one common transmitter (aka the bridge) to send one siginal, IR at 40khz. Each car will carry their own receiver to capture and record the beacon when it goes under the "bridge." I built a very rough counter and have sucessfully tested using a remote control. I need to filter out the daylight some more but the counter part works, if I could just get my transmitter together the way I want. My plan is to be able to hook the transmitter bridge up to a car battery (12volt) and the way I have it design, I will be able to add or remove sections of 4 foot intervals to my bridge for changing track shapes, locations (we race in parking lots). I figured I would have up to possibly 160 leds over 20 feet. Using 32 leds in every 4 feet, 8 leds in every foot, I'll have a 40khz emitter board/circuit every foot. These will be connected parallel to the main 12volt supply. Now, these are not slot cars, so break beam systems will not work because at any given moment, a car could pass the counter at any given 20 foot section of asphalt. To keep from broadcasting 6 or 7 different signals from the cars, there will be more than one racing at the same time, I decided to have a common transmitter, the bridge, at 40khz, shooting down at the track, and each car will carry its own onboard lap counter and IR receiver.