Building a timer?

[jmcoreymv]

Ive been trying to find a way to build a timer for some of the labs I have to do so I dont have to use a stopwatch (because I have a very bad response time). What Ive been looking to do is use something like 2 LEDs with photo transistors to create two separate light beams. When something breaks beam one, the timer starts, and when it breaks beam two, it stops. The problem is I dont have much knowledge of how to build something like this with the timing circuit and LCD display. I do have soldering equipment and I know how to solder. I cant seem to find any plans on the web for something like this, any ideas?

 

[Lithium381]

that idea......it's a good one, but it's quite expensive, at least the finish product is, my teacher said so anyways? i'll have a look around for you..

 

[Lithium381]

This looks interesting

Maybe two of those, and then take the signal feed from the buzzer, tie that into the button/switch for the timer and you'll be set(of course you'd need two of 'em)

not sure how accurate these are or how fast they would react........just an idea, good luck

 

[jmcoreymv]

Would it be possible to setup the beam with an led (powered by a battery, so it isnt wired to the main system) and then have the beam received by one of these phototransistors and somehow hook them up to a timing circuit like the 555 timer.

 

[jteef]

To get the output to a LCD i think you're gonna need a microcontroller of some sorts. The project would be a snap with one of those, but I believe it costs a couple hundred to get started with a programmer and all that stuff.

Interfacing basic logic chips to an LCD isn't going to be fun. I don't know what kind of precision you're after. 4 bit and 8 bit counters are common.(I think thats as complicated as we got in our lab) The problem is getting the output of the counter to something you can read. You could connect the output of the counter to LED's and read the binary number and multiply on your calculator times the period of your oscillator frequency.

jt

 

[jteef]

Maybe the easiest and cheapest? option would be to take a stopwatch apart and connect your LED/photodiode system to the buttons on the stopwatch.

jt

 

[jmcoreymv]

That taking the stop watch apart seems like it would work really well...hrmmm

 

[etech]

Do you have a laptop?
World's Least Expensive Pinewood Derby Timer

Plans for a mulitple timer system, modify according to your needs.
The Do-It-Yourself Race Timer


Actually the idea of using a stop watch is pretty good. It shouldn't be too hard to use a phototransistor to close the switches of the watch.