[LinuxGirl]

Hi,

I am doing a science fair project where I use a microphone and a light sensor to measure how far away lightning struck or a firework went off by the delay from sensing the light to sensing the sound. I have built a device that should work for sensing the light and sound (though I will probably make improvements to it later on), but I now my biggest problem is I need a way to test it.

I can wait until there is a storm to try it out on some thunder, but I think I need some other ways to test it, too. I could maybe test it with fireworks, but I would need the big kind that get launched into the sky and i don't think there are going to be any firework shows this time of year.

I need help brainstorming any kind of thing you can think of that would make a blast of sound at the exact same time as a flash of light. Can you guys think of anything?

[dragonstar57]

firecrackers?

[SMF]

What you need is a sound activated photographic flash unit. Activating it at 100 meters with a starter pistol should give you about a third of a second difference between the flash and sound. You can figure this pretty accurately for a specific distance, temperature, and air density. This sort of flash setup is rare but available. I would try talking to a professional photographer or to someone who is a gun hobbyist. They may know someone who can help you calibrate your device in real time. For a less accurate test you could use a camera to flash your device up close and then making a loud noise two seconds, or whatever, later. SM

[Mr Skeptic]

If it is dark enough, you can get away with much less light. Hitting a piece of flint with a hammer, perhaps? You could use a hammer as part of an electric circuit, but not with an incandescent light because they take time to heat up. Maybe with an LED. Or small firecrackers, if those are legal where you live.

[Svetoslav Pavlov]

Use motion detector and/or alarm system

[LinuxGirl]

At first I thought firecrackers would work, but they are not legal here and it would probably be pretty inconvenient to do a lot of testing with a big firework that I would have to light. But, I was eventually able to figure something out. I hooked up a light bulb and a buzzer in a circuit with a push button, so when I pushed the button, it made them both flash and beep at around the same time. By testing it at known distances away, I found that it took about 30 ms for the light bulb to heat up and actually start shining, and I was able to work this offset into my program. So far, I have been able to get it to have +- 10 m accuracy, but I hope to get better than that. Anyway, I just wanted to let you guys know that I'd got it working and thanks for your suggestions!

[imatfaal]

Way to go! Remember that atmospheric conditions will affect speed of sound - ie increased air pressure. I would be tempted to set up a control set that I know distances of to calibrate everytime you measure