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Tuesday, 11 January 2011, 18:54 | Track Building | 1 Comment | Read 7278 Times
by Jeff B


Most lap timer suppliers will sell you a pre-wired I/R sensor cable for about $40 plus shipping. This article will show you how to make your own for less than $15 using an old printer cable. This sensor cable will work with Trackmate, LapTimer 2000 and UR30 lap counters.

You will need up to 4 – I/R sensors from Radio Shack, part number 276-145. You will also need an old printer cable with a DB25 male coupling on one end. Some small plastic heat shrink tubing is helpful, but not mandatory; electrical tape may be substituted.

You will need the following tools: a vise or a clamp, soldering iron, solder, rosin flux, wire strippers, xacto knife, and an ohm meter.

The first step is to cut off the end of the printer cable that normally plugs into the printer. This leaves you with a cable with a DB25 male connector on one end. Using an Xacto knife, slice the insulation length-wise in the cable for about one foot. Then peel back the insulation and trim it off. You should see a bunch of color-coded wires and an un-insulated wire and perhaps some foil shielding. Trim off the foil shielding and the bare wire.

Next you need to identify which of the color-coded wires are to be used. Using the wire strippers, remove about ½ inch of insulation from each wire. Using a vise or a clamp, secure the DB25 male connector to your work bench so that you can easily gets to the male pins. Use the diagram below to identify pins 10-13. Now using an ohm meter, place one of the meter’s leads on one of the wires, then touch the other lead to the pins on the printer cable. Check each pin until you determine which one the wire is connected to. The goal is to find which wires connect to pins 10-13 and which ones connect to the ground pins(18-25). Once you have identified the wires that connect to pins 10-13 and four or more ground wires, trim back the unused wires. (NOTE: it is a good idea to have extra ground wires identified just in case one doesn’t work properly)

If you are using heat shrink tubing for insulation; then cut your tubing to about 1/4” longer than the leads on the I/R sensors. Take the wire for pin #10 and slide the tubing over it. Next, solder the wire to the short lead of one of the I/R sensors. Now take one of the ground wires and slide the tubing over it, and solder the ground wire to the long lead of the sensor. Slide the tubes over the solder joints until the bare leads are completely covered. Repeat this process for the three remaining sensors and you are ready to test your sensor cable.

Download LapTimer 2000 and install it on your computer. In the setup select LPT1 port and I/R sensor. Select the TrakMate setting for the sensor. With four lanes displayed on the screen, you should be able to generate a lap for each lane by flashing a light across your sensors. If one does not work properly, then try a different ground wire on that sensor.

Once you are satisfied that all four sensors work properly, you can apply some heat to the tubing to shrink it around the connections, and you are ready to install the sensors in your track.

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  1. Jeff B says:

    After a year of use, I had a problem with one of the Radio Shack sensors. The way these sensors work is the light beam closes the circuit that the sensor is wired to. When the car crosses the beam, the circuit is opened, triggering a lap in the software. When I started the lap counter, a lap was immediately registered on one lane even though no car had crossed. Plus that particular lane was unable to count any more laps. This indicated to me that the circuit was open and would not close when the light was applied. A replacement sensor fixed the problem. I recommend keeping a spare sensor, or two, on hand with lead wires attached. That way if you encounter a bad sensor it will be an easy fix.

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