I want a way to do long exposures (>30s) without needing to keep my finger on the button or my eyes on the clock as I might be doing other things with both, like manually guiding a telescope. I want precise exposure times for reproducibility. I want to be able to optionally do this continuously to create a timelapse. It also needs to be portable and low power.
This was my first micrcontroller project that wasn't just messing around. A dual 7-seg display from an old VCR and an MSP430F1123. A 32.768 khz watch crystal keeps the time and you set each digit with a +1 and a +10 button. Both buttons at once cancels an in-progress exposure. If you keep the trigger button pressed, the exposures will auto start as the timer expires and if the camera is not set to bulb, this can be used to create normal light timelapses. If the camera is set to bulb this can be used to create low light timelapses. The flexibility is limited as you cannot put 'dead space' between the exposures, though it would be a very easy software tweak. A switch on the side controls power, and a second switch on the front changes between seconds and minutes.
If I did things over again I would use a smaller case with enough room for a li-poly cell. I would also use audio jacks instead of wires so that this could, for example, be daisy chained with the RF trigger or any other device designed to trigger the camera.
MSP430 Source Code
Can be found here (For reference only, all rights reserved)
2009 Jasper Nance KE7PHI