Hey, look at that, my blog website is still alive and working. Last post was Sep 2010, a long time ago.
I’m planning a trip to the desert, and one of the things I wanted to make for myself were time lapse movies of sunrise or sunset, and the night sky. My DSLR does not have a wired remote capability and Hoya has decided not to include an interval timer on their low end DSLR
I could have purchased a timer off ebay, that claims to be compatible with every DSLR ever made but those claims make me skeptical. I also did not care for their user interface. So, many months ago, I tore apart one of the Pentax IR remotes, to see what makes it tick. It was a simple design on the inside, a rather large micro-controller with external clock, a transistor, a capacitor, a few resistors and an LED. The trigger button was one of those resistive pad-switch types. Originally I thought I could just trigger the remote by pulling one side or the other end of the button high or low. This did not work, and when I scoped it, I discovered a handshake was employed between the two terminals of the switch, both leading to micro-controller pins. So it looks like Hoya didn’t want people hacking the remote directly.
Switching to plan B, I tore apart an old pioneer cd changer and harvested its IR decoder chip. Following some arduino code from Lady Ada, I tried to capture the timings of the IR signal using a PIC. This worked to a degree, and probably warrants further study down the road, but I couldn’t get the pulse train quite right and so the camera would not respond.
Abandoning the learning-remote line of thought, I connected the IR decoder to my o-scope and manually measured the pulse train. It was only 26 msec, and consisted of 15 transitions. 13 msec on, 2.8 msec off, and then 1 msec on/off repeated eight more times. Using the 12F683 chip (one of my favorites), I had access to an 8MHZ internal clock and a hardware PWM module. Microchip claims the hardware pwm maxes out at 20khz, but I had no trouble getting a stable 37khz carrier out of it. Then I whipped up a little subroutine in proton basic which toggled the carrier on and off with the appropriate timings. I had setup the pic’s pwm output on channel 1 of the scope, and output of the ir decoder on channel 2. I could fire the pentax remote at the decoder and compare it to my pulse train from the pic. When they were an exact match, I got the camera and presto, it started snapping pictures.
That schematic is what I’ve worked out for a bare-bones version of the remote. A single button is used to program the interval, there’s a status led and room for two IR emitters. My current prototype is only using one emitter, because that is all I have right now. I’m also using a 2N3904 which isn’t ideal, but it was working on the breadboard and now it’s soldered in place. I just now looked up the specs, and the poor thing is only rated at 200ma collector current – that could explain the lack of output power I’m seeing on the emitter.
In interest of saving time, I didn’t make a PCB for this revision, but I’ll probably do that for the next prototype. All point to point wiring, I tried to be neat. I used a tiny SMT resistor to drive the transistor, it worked out real handy.
The timer and two AA batteries fit in this mint tin I’ve been saving for years. I don’t know if they are still in production; I would like to get a few more.
I field tested the timer at tonight’s sunset – I’m trying to figure out how to convert a bunch of jpeg’s into an avi now – stay tuned!
Update: Here’s the video, turns out Picasa can generate a timelapse … only 8 seconds, need more frames!