CHEAP LAP TIMER

Step one was to get the nice software from Gregory Braun http://www.GregoryBraun.com His timer was build for slot cars, and provides timing for 4 channels, The software uses a port on the PC, I used the Parallel Port, to receive signals from a phototransistor that is being activated by an Infrared LED.. When the Infrared Bean is blocked by the passing car that triggers a lap and the time is displayed. Now we can't easily port this timer to Zipzap racing but we can still use it for experimenting and for timing laps. The reason we run into problems is that the slot cars are always on their individual tracks so putting the IR emitter and detector across the slot in each track can keep track of the 4 cars. In mini RC racing all cars are all over the track at the same time, so either could break the beam and render the results useless. For now we can set this up for single car laps, you could tweak your car for the particular track and compare REAL time numbers. NO Guessing involved. Also There's a neat trick to set this timer on a drag strip by using 2 small mirrors. more of that later. THE PARTS: 1- PC.......................YOU SHOULD HAVE ONE 2- Software................FREE 3- Parallel Cable.........From a scanner. 4- phototransistor.......~$1.70 RadioShack # 276-145 5- Laser Pointer*.........$4.50 including S&H  www.wholesaleforeveryone.com *The reason we need the laser pointer is because the range of typical IR diodes is only a few inches and might not be enough to set it across a miniRC track. That's it to get you going, you can get as fancy as you want as you will see on my prototype But to get a quick and dirty setup going you would just put the phototransistor across let's say pin 25 and 10 on the 25pin female connector at the end of the cable. and shine the laser at it. Run the software and everytime you break the beam you get timing between intervals. Sweet. The software explains how to set it up. but it's this simple.

MY TIMER

I used an old Camcorder Cassette cover to hold the electronics. Another nice feature of the software is that it lets you control a data pin (pin2) it toggles 5v on and off. the author intended this to be used to trigger a relay to give power to the track, hence the name of the feature "Track power" I took advantage of this by having pin2 toggle power to up to 4 lasers. You can hardly see the 4 channels for the phototransistors and for the 4 lasers but they are there.

Another view

Here's an inside view with the single toggle pin2 wire and the two power wires. You can't just run the 4 lasers from the 5V pin2 signal because the lasers will draw too much current and you'll fry the parallel port circuit. Instead I had to build a parallel port controling circuit to drive the relay that will in turn trigger the 4 lasers. The circuit requires its own power so I'm bringing in 12V from the computer power supply in pins 16 and 18 that are not currently used by the software. I build a Voltage regulator circuit to drop those 12V to about  4.1V, no need to run the lasers at full brighness at 4.5v. The circuit is adjustable so I can play with the output voltage.

Here is the tap of the parallel port plug in the PC. This plug will go on the back of the PC and the timer cable will plug to it.

A closer look of the parallel port relay controlling and the voltage regulator circuits. Both are quite simple to build from off the shelf components. For more info on the relay controlling circuit visit: http://www.hut.fi/Misc/Electronics/circuits/parallel_output.html The voltage regulator is a very common circuit you can find doing a simple search. This three terminal circuit uses the LM317 regulator, a 240ohm resistor, a variable resistor for adjustment, and 2 caps. NOW I can turn the lasers on and off from the software by pressing F10. :) Questions?? wdiaz03@yahoo.com

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