Bicycle timing system for sprints and time trials
Bicycle Sprint Timing System 

Warren Beauchamp - updated 1/7/2012

In the past we often had to time the sprint events at the various HPRA HPV and recumbent bike races by hand, which was not entirely accurate, and was not admissible for records. Wally Kiehler from the Michigan Human Powered Vehicle Association asked if I could find an electronic timing system for the Michigan 200ft flying sprint, which the MHPVA would pay for. The MHPVA would loan it out for the other HPRA races in our racing series.

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. 

I posted my dilemma on the message board, and Jeff Wills pointed to the bikecurrent list, where Karen pointed me to a list of circuits, one of which looked to be perfect for me. It was a simple 555 timer circuit, and used a relay to isolate the stopwatch's start/stop button. Time to build it. I bought a $10 stopwatch at Target, and $11 worth of electronics from Radio Shack. After some microsurgery, I was able to connect external wires to the start/stop button of the stopwatch. 

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 circuit worked nicely! Now it was time to package it up. After rustling through my old electronics junk for a while, I had an idea. Can I fit it all inside the stopwatch? After hours of careful soldering and assembly, I crammed it all in! Amazingly, it still works. An LED shines through the smoked plastic body of the stopwatch to show when the timing circuit is activated. Cool!

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: 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.

Next we will need to wire the tape switches to the stopwatch. I'd like to get 1000 feet of wire. This will be long enough for our 200 Meter races, plus enough extra to run from one of the switches to the stopwatch. Coax should be used to avoid RF interference.

This place: has 1000 feet (300 meters) of nice extra thin rg59u for $99 or 500 feet for $65.

Here's the Frankenstein stopwatch all put back together. 

I mounted the stopwatch to a small plastic box with some silicone glue. In retrospect maybe I should have used Velcro, as in a couple years it will need to be peeled apart to replace the 386 watch battery in the stopwatch. The box is just big enough to hold the 9V battery that powered the de-bouncing circuit, an on/off switch, and a power LED.
I found a nice plastic box to store it in.

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

The two 15 foot long timing tapes arrived this week. I hooked them up to the stopwatch and did some testing. The tapes trigger nicely with a bike rolling over them and the de-bounce circuit allows enough time for a bike rolling very slowly. I also put a 10K resistor in series with the switch to simulate a reeeeeally long wire and it still triggered, so I don't think we will have any problems with that. The tape switches are very flexible and supple. The TapeSwitch rep had some concerned about bikes damaging the switches, but agreed that taping them down with duct tape should protect them.
Garrie Hill graciously donated a spool of about 800 feet of multi-conductor, very tough wire, rolled onto a convenient hose reel. I added quick-disconnect connectors to the tape switches, stopwatch and "big wire", to allow the system to be set up and torn down quickly. Since there is only one triggering circuit to this system, both the start and finish tape switches were connected to the same two wires in the long cable. Testing proved that it works fine. Time for the acid test!

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!

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 to water. 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. 

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.

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 but is recommended because there is more RF noise out there all the time, and the spool of wire acts like a really long antenna.


Timing Circuit Parts List:
Quan Item Radio Shack Part#
2 15 foot 131-A tape switches
1 cheap stopwatch with big buttons
1 200 meter roll of wire
1 555 timer 276-1718 
2 2K resistors 271-1325 
1  47K resistors 271-1342
1 100K resistor 271-1347
0.1uF capacitors 272-135
1 22uF electrolytic capacitor 272-1026
3 diodes 276-1102
1 12v reed switch relay (tapeswitch) 275-233
1 5v reed switch relay (stopwatch)
1 9 volt battery connector 270-324
1 9 volt battery 
1 Project box and PC board combo 270-283

Not on the schematic above was a red LED with a ~330ohm resistor inline in parallel with the existing diode across the relay coil that controls the start/stop stopwatch button. You can see it on the proto-board above. This was jammed into the stopwatch with the rest of the circuitry, and is visible through the smoked plastic stopwatch housing. This was added so I could see when the de-bounce circuit was running.

After 4 years the timing system is still running on it's original batteries, and has been working great. The only problems seem to occur on extremely hot days when the timing tape seems to get "stuck" after being run over. On those days it's best to just tape the timing tape at each end. When it gets stuck, shaking the tape around a bit seems to un-stick it. We have also been using this system to time the HPB races for the past couple years, substituting a normally-open pushbutton on the end of a long wire to start the timing, and using the pushbutton the the stopwatch to stop it.

This year Sean Costin donated both a new spool of wire, which is much thinner, therefore easier to transport, and two Robic stopwatches. The advantage of the Robic stop watches is that they are actually calibrated, and that they time own to the thousandth of a second

The idea was to build two new timing systems to replace the old HPRA one (which still works), and to send the other to the Dutch HPV racing group to ensure they provide the WRRA with electronically timed race results.

I built the two new timing systems in project boxes and built up the circuit on a breadboard.  I ordered all the parts from Mouser Electronics. Here's a list of the parts I purchased. Note: two 12V relays are specified in this list. Later I changed out the relay that triggers the stopwatch to a 5V reed relay.

Here's the built up circuit showing the LED indicator for power and "triggered". You can see that this enclosure has a built in spot for the 9V battery.
Here's the completed timer. On the outside is the on / off  switch and an RCA connector to the tape switch, as well as the LEDs.

The old timer had a "feature" where if you turn off the timing circuit or unplugged the cable to the tape switch while the timer was running it would trigger the circuit. This was annoying because when the races are multi-lap it is nice to be able to disable the triggering so the racer can hit the pressure tape in the middle laps without stopping the timing of the run.

Fortunately this new timing system does not have the same issue as the previous one. We can now do the multi lap sprints and just switch off the timing circuit during the middle laps, then switch it back on before the finish lap, and the timer keeps running until the racer crosses the tape switch on the final lap.. I think it's a different model of 555 timer that allows for this, but I'm not sure.

The new timer had an issue where when the 9V battery was not at 100%, the stopwatch would not get triggered. I traced it down to the secondary reed relay that triggers the stop watch. Apparently the 555 timer was not supplying enough current to trip the relay when the battery was not new-ish. I changed the stopwatch trigger relay to a 5V relay (updated parts list and schematic above), and now the timing system works down to about 8.5V.

I replaced the power indicator LED with  an "LED Battery level voltage monitor meter indicator" from EBay. The LED has a button to set the modes and it was not easy to set up but it works well to display the battery level, showing green, yellow or red depending on the battery condition. Note: no inline resistor is needed with this voltage monitor LED.

Also we obtained two new tape switches. The old ones had become kinked over the years, which made them very finicky.  

The timing system worked well throughout the 2015 racing season.

Recently I was thinking about inexpensive ways to trigger this circuit with an optical sensor and laser. Here's an inexpensive circuit that would work well using a phototransistor. (Vishay TEPT4400. $0.25 from Avnet) It looks like the 555 timer could be driven directly by the phototransistor rather than using the relay on the input side. A cheap laser pointer could be used to trigger this system. A light blocking tube would be needed to block the sunlight and only allow light from the direction of the laser. Lining this system up would be difficult in the direct sun. I think a small trigger beeper would work well on the output side to replace the trigger LED.


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