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Picture of External Trigger for Stop Watch
This instructable will show how to add an external trigger to a stop watch so that it can be used for event timing from circuits. It's designed to accept from 1.5 - 50 VDC, though I've only tested it from 1.5 - 9 VDC.

Step 1: Dissemble Watch

Picture of Dissemble Watch
01B - Cover Off.jpg
01C - PCB Out.jpg
Take the watch apart.
 
VaTech069 months ago

Thanks for the post. Appears that the external trigger of 12 volts (constant, lets say a motor running), would start the stopwatch upon application of the trigger voltage. This constant voltage would maintain transistor in conductive state. When the 12 volt trigger voltage went away (motor stops) the clock would continue to run, stopping only when the 12 volts was re-applied to the trigger. Is this accurate? I am not an electronics guru. I ask because I have made my own stopwatch modification which does indeed 'pulse' the start/stop contacts of the stopwatch upon external 12v power on/off. It uses relays and capacitors but if there is a way to do it with transistors, it would be much preferred. Yours seems so elegant and I am hoping my understanding is wrong. Below is my 'final product'

https://www.youtube.com/watch?v=fPy2otYtT1Q

neat, what are you planning on using this for?
vreinkymov (author)  amandaghassaei3 years ago
A microcontroller that I'm wanting to use has a discrepancy between the datasheet timing and the simulator timing so I want to see how much time analog-to-digital conversion takes. I figure I'd be able to put the analog-to-digital conversion inside a loop and then calculate it from there.