100m race timer

Hey all! ;D

I want to make a 100m race timer with a sensor to sense the start and a sensor for the finnish, i was thinking of shining a Laser into an LDR and measuring someone run through the laser that way? what do you think? and how will i send data from 100 m away? any ideas?


Yes a laser sounds good. However, you might want to pulse the laser and use a photo transistor and amplifier to minimise interference from ambient light.

As to getting the signal over the distance, I assume you don’t want to run a long wire so I would guess that wireless would be the best. Just a straight forward TX and RX would probably do.

Thanks, just a another question, why pulse the laser?

why pulse the laser?

So that you can distinguish it from constant sunlight more easily.

Will just shielding the sensor work…?

It might, being a laser you could put the sensor at the end of a tube but it is more tricky to set up and you still have some problem with stray light.

Do you have any other suggestions for detecting a person running past a specific point?thanks for the help

How about a web cam running some image processing software. You only need look at a small vertical bar of the image to see if something has moved and trigger the timer.

I’m looking to do something similar… I saw this on you tube, Laser Tmer version

But wasn’t sure what bits of equipment I would need. I’m new to electronics, but not to programming… Any advice?


What kind of accuracy should i expect? and how long will the wireless signal take to register, approx?