I’m a software engineer, I’ve had no training in electrical engineering other than hanging around my electrical engineer brother more than thirty years ago. This has not stopped me from attempting to hack an electronic solution to an issue that I was having. The problem was that I bought a time lapse camera which was supposed to support shooting in darkness with infrared light. Which it does. However, it doesn’t have an infrared light source, so you have to provide one. Getting a battery powered IR light source that will last all night is more expense than I wanted. I found an inexpensive IR light source from Polaroid however it has a one hour run time. I noticed that the camera had a port on the side that looked like a flash control cable port… it was labeled as such in the documentation but there was no mention of how to use a flash, how to enable the flash, etc… writing to the company produced no response. I thought perhaps the cheap light source would last all night if it was only on when I was actually taking a picture.
So I got a cheap flash control cable and cut one end off and stripped the wires and using a multi-meter I found that indeed there was a signal there that was in sync with shutter. I remembered that a transistor could be used as a switch and I wondered if anyone made a module for that which I could just trigger using the output of the flash control wire. And thanks to all the STEM classes and such there is such a module and I was able to wire it up between the battery and the light and make the light go on and off using a 9v battery. However, the voltage from the camera trigger was 1000 times too weak to turn on the MOSFET so I then I remembered a thing called an OPAMP which could take a small current and multiply it by a gain. I got one of those and put it between the camera and the MOSFET. I needed a 5v or better power source for the OPAMP so I put two blocks of three AA batteries in series ( which gets you to 8v ) and the OPAMP board had a handy constant 5V out so I could power everything downstream off of that. This also converts the light into having replaceable batteries instead of internal recharging which is faster and easier because you can use one set and charge one set with no waiting.
I could show that the light was going on now when the shutter ( well really focus and shutter ) signal was on, which was great. I was so proud of myself. Then I did a test. I put the whole rig in sealed up box (no light) covered all the red/green led’s on the boards with a small cover box and set up a time lapse with IR of an old mechanical watch with hour minute second hands. I got…. complete blackness. Turns out that the signal to the flash turns off before the shutter actually opens, makes sense because flash units have a specific flash timing to be on for an amount of time after the trigger.
So, I needed a way to keep the light on after the trigger. I thought about perhaps a discharging capacitor? But it seemed like it wouldn’t have time to charge before the shutter? I searched around and found a cool universal timer module that has a trigger mode. It will turn on it’s output and keep it on for a programmable duration, exactly what I need! And it appears it will replace the MOSFET in the circuit I have. I’m waiting for it to be delivered to try again.
I’ll write up the results in part two.
Cheers!
P.S. I’ll share the parts and where to get them etc… IF I get this to work…
