Warren Beauchamp 2/10/05

I had been thinking of building a simple timing system for some time, using two timing tapes, and a cheap stopwatch. The tapes would be wired into the stopwatch to start and stop the timing.
 
The only issue was that a bike will depress the tape switch tape twice every time it hits the tape, which would both start and stop the timing. Some method of "de-bouncing" the switch would be required. I figured that a bike going 10MPH would have about .25 seconds between the first and second tire hit, which is about 10 times too long for an integrated de-bounce circuit. 

Following the schematic diagram, I then built the timing circuit and connected it to the stopwatch.

Here it is on the prototype board. I adjusted the circuit to provide about a 2 second period where the switch tape could be triggered multiple times while the stopwatch was triggered just once. 

You can click on this picture for a larger image.

The 9V battery that runs the timing circuit is still external, and I still need to find some way to mount it to the stopwatch.

The timing tape will be purchased from: http://www.tapeswitch.com. This manufacturer offered us 15 foot tapes for $98 each. 

This picture shows the electronics crammed into the back of the stopwatch. There was some space on each side of the display which proved to be just the right size.

Here's the Frankenstein stopwatch all put back together. 

The members of the MHPVA approved the purchase of the timing system at their winter meeting, so the tape switches are on order...  

At the 5/21 Morris, IL HPRA HPV races, the timing system was put to the test. This race had a 1 lap individual time trial that needed to be timed. Each rider would run over the tape once to start the timing, then run over it again to stop the timing. 

A single timing tape was used, and it was stretched across the track at the start/finish line, then covered with a strip of duct tape to hold it down and provide added protection to the tape. 

The timing system worked great, and operation was extremely simple for the person running the stopwatch. All they had to do was push the "reset" button between runs. 

This weekend I will deliver the system to the Michigan human powered vehicle association. They'll be using it to time the hill climb, 200 foot flying start TTs, and the drag races. Cool!

6/17/05
At the 6/11 Waterford,  MI HPRA HPV races, the timing system worked well until it started raining. It appears that the system is very sensitive. We will add waterproof connectors to fix this issue. Also you must be sure to tape the timing tapes down carefully. If they are taped down too tight it will trigger the timing tape. 

Conclusion:
This is an easy to build, inexpensive and extremely foolproof timing system for timing bicycles or any lightweight wheeled vehicles, over a measured distance. If you had to purchase all the parts new, it would still cost under $500. It can be run without any knowledge of timers or timing. All we need now is a programmable pocket calculator to quickly convert the times into average speeds.

8/09/06
Here's the schematic and a parts list. Note that I added another isolation relay to the input of the circuit to prevent effects of parasitic resistance, noise, and dampness from affecting the timing circuit. This additional relay is not needed if the input switching is fairly clean.