Lightning Detector.

[cjdelphi]

I came across this Circuit...

I don't really understand the role of the 555, the 555 is set to monostable/1 shot, when current is inducted to the 4ft long copper wire, the voltage/current goes through this circuit, but why would you use the 555 trigger pin for a single pulse? why not simply have the transistor feed straight into the optocoupler?...

i'm missing something here, I'd love to one day build a lightning detector but knowing me i'd probably want to get as close to a storm as possible a few times just to make sure it works lol... anyway what's the role of the 555 in this circuit?

 

[Harald Kapp]

The impulse from the lightning may be too short for the arduino to detect it. Therefore the 555 "stretches" the impulse in this monoflop configuration.
http://www.allaboutcircuits.com/vol_6/chpt_8/4.html

Harald

 

[cjdelphi]

The time is too short for the arduino and not 555?

 

[BitHead]

Yes - the 555 looks like it's going to generate a nice, long 1/2 sec.-ish pulse when it's triggered by what could be the very short-duration (sub-microsecond) spiky tip of a lightning strike detect. That's this monostable's job - taking bouncy, spiky, weak transient 'low-going' voltages and turning them into predictably clean-edged, long-duration ones. The monostable is also used a lot for de-bouncing push-button switches being pressed by hesitant, lightly pushing fingers so quick-responding uControllers don't do something twice - or ten - times.

 

[(*steve*)]

Also it will essentially integrate pulses over half a second. This means that many pulses generated from the strike get counted only once.

edit: integrate is the wrong word