I’m after something to take lap times on my pump track without spending a fortune.

So far the options seem to be:

– cheap watch on handlebars with a larger button soldered into the start/stop switch

– home-made light gates of some type and stopwatch

– android app (are there any that use the camera as a motion sensor to trigger a stopwatch?)

– angry impatient girlfriend and stopwatch

I’m not afraid of a bit of soldering but I’m no electronics expert. Anyone made their own system?

I’ve got one of these:

It’s designed for swimmers to wear on a finger & count laps, but works fine attached to your handlebars and using your thumb to press the button to start / stop. About £25.

This might be a reasonable place to start

http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1290903871

You want to time repeated laps on a pump track AND have a girlfriend? Pfft.

I like hacking stuff, I’d be thinking about an arduino board, as above and some kind of sensor.

Probably the simplest way would be an infrared light sensor / emitter pair and building a light gate out of it. You can buy infrared emitters and receivers specially designed for this.

Possibly, one could a buried capacitive sensor of some kind – I understand if they’re made big enough they can detect cars, although I don’t know how big a battery you need for that!
http://www.arduino.cc/playground/Main/CapSense

It would be extra neat if you could work out some way to uniquely identify riders, so you could time multiple people, I think that would need some kind of RFID system. You’d need to bury the sensor mat under the start line, or use antennas at the side (I understand you can stick the RFID tags on people’s helmets, and use a big antenna to read them).

In terms of the Android app, I don’t know of one, if you were happy to leave your phone pointing at the right place, I don’t see it being super hard to write, don’t have time right now, otherwise I’d hack you something up myself.

a light gate – like the ones used for intruder alerts at windows, etc.
Some sort of microprocessor board that had DIO ports to get the signal in. Google spreadsheet and a SIM card to live update the time for each break of the beam. Then your girlfriend can stay at home with a cuppa and check your progress on-line.

Can be doubled up to time DH runs too!

Something like this

http://www.tredz.co.uk/.DRC-X-Monitor-SP1-Universal-Lap-Timer-Stopwatch_44742.htm

Or if you want to get the soldering iron out replace the button with a photransistor and make a light gate

@nickjb I like the look of the DRC X-monitor. I can try having the button on there at first and sort out some gates if I don’t get along with it. It seems they can only be pre-ordered for the moment though.

The rest of the ideas look good but a little too expensive/advanced for my level of programming and soldering.

Thanks for all the replies!

This is on my list of projects to do, along with a dual slalom timing system (I’m currently writing the software for the DS system, with the next step being to connect it to the start gates, followed by accurate finish line timing)

What you want can be done fairly easy with an arduino, a light gate, a couple buttons, and some way of outputting the results (LCD, or computer).

However, the cost is all in the light gate, if you want something repeatable/accurate. Arduino is £25ish, LCD £5ish, buttons £couple.
You’re talking upwards of £130 for a thru-beam set-up, but I’ve still not decided on what one, as everytime I look at spec sheets, my head starts to hurt!
I really need to sit down, work out the required response times for a tyre/rim whizzing past at XXmph, then find something suitable.

Off course, you could always use something like a pressure pad, but then you need to make sure you put it somewhere that you’re likely to have weight on it while going over the top of it.

Cheeper/more reliable than a DIY light gate might be some kind of wand?

GF or CF pole ~3mm diameter, microswitch on one end, some kind off box to stop the switch being crushed.

Stick it on the floor and everytime you run over it the switch closes, enough flex in the rod so that it deflects once its pressed the switch. Add a thyristor, transistor, capacitor and resitor wired top to switch on for say 2 seconds so it only records the first event (front wheel), the wire it upto a suitable stopwatch that can record laps.