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camera trigger for lighting pictures

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Well... just looking over the schematic now. To reduce sensitivity, it looks like two fairly easy options...


1) Put a 1MegOhm POT in place of the 1M feedback resistor on the first stage 324 op-amp (the resistor between pins 6 & 7).

One leg of the POT to pin 7, the wiper to pin 6.

Adjust the POT as needed - a lower resistance will mean lower gain, and less sensitivity.




2) With circuit ON, measure the voltage present at pin 13 of the final stage 324 "comparator".

Turn circuit OFF.

Disconnect the circuits reference input to pin #13 of the final stage 324 "comparator".

Wire up a 10K POT with one end to V+, the other end to ground, and the wiper to pin 13.

Set the POT at a middle point of its adjustment.

Power up the circuit and adjust the POT so that the voltage at pin 13 matches the original measured voltage.

Make minor adjustments to the POT to alter the reference voltage (triggering level).


Like to see the pics if you get some!

Edited by Archilochus

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Thanks for the info. I've been learning as I tinker with this stuff, lots of reading, and the feedback resistor was going to be the place I started for making it less sensitive. I wasn't sure if it would work or not but you just confirmed my thinking, thanks. As for the second option, I would've never came up with that but I think I understand how it would work, it's just a variable resistance in place of the voltage divider resistors.


Which one do you think would be the better option and with option 2 can the voltage divider resistors stay in the circuit or do they have to be removed?


I'm glad that there are people on here who know what they're doing.


I'll definately share the pics if it ever storms here again while I'm home.

Edited by phil

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Hi Phil,

I'd go with the first option since it's easier. I just added the second option in case there was some reason you didn't want to alter the first stage amplier, or maybe didn't have the parts laying about to try the first one.


If you were to use the second option, the original voltage divider resistors should probably just be be left in the circuit.

At a glance, it looks like you could remove them with no problems, but it can't hurt to leave 'em in just in case (they will drain a bit of power though).

Edited by Archilochus

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Looking forward to seeing how this works. I tried the other way, lightning in the distance made the sky all lit up like daytime while I wait for the right one.



If you use a higher f-stop you should be able to minimize the distant lightning blowing out the sky. Also, I wouldn't hold the trigger down for more than 10 seconds or so for each frame.

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