Digital ChronoMeter

Good day to all!. I'm looking for a cheapest and an easy to build digital Chronometer for my airsoft gun. I'm tired of using the old soda can technique. Please, help me find one. Many thanks!

scottraynor said:

Good day to all!. I'm looking for a cheapest and an easy to build digital Chronometer for my airsoft gun. I'm tired of using the old soda can technique. Please, help me find one. Many thanks!

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I don't know anything about a soda can technique. Are you trying to measure exit velocity of an airsoft gun?

a simple microcontroller and some IR emitter + detectors placed in the barrel should do it. you'll have to rely on a known-good method of determining velocity to calibrate the gizmo, or easier yet just use it as a relative "more/less" kind of reading.

the first photodetector pair starts a counter, and the second pair stops the counter, throw a little math at the result and you've got a velocity number

Hi Scott
Funny you should want to construct your own chrono, I had the same idea a couple of days ago. I haven't gotten any longer than to purchase some photo diodes and IR diodes.
My version will probably be very simple. I imagine a AT89C2051 processor clocked by a 12MHz crystal (gives a machine cycle frequency of 1MHz which makes the timing a little easier).
The 2051 has two external interrupts which will each be trigged by some sort of simple circuit which will trig on the breaking of the light beam emitted by the IR diodes. The interrupts are located on port 3, so you could use port 1 to control 3 7-segment displays. These will with the right code show you the muzzle velocity in fps or m/s as well as the ROF. Anyway that's what I plan to build.
I never used the soda can tecnique myself - I just don't think its serious enough - So for us electronically minded, what else is there to do than make a chronograph of our own?