Pentax IR Interval Timer

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.

Cam Remote Schematic

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!

5 Replies to “Pentax IR Interval Timer”

  1. In this era of just purchasing everything off the shelf and throwing out old stuff it is so refreshing to see people that can recycle bits of old equipment and make something new.
    I wouldn’t know where to start on a project like this but more power to you for this and future projects.

  2. I have a Sony a-230 and a-330 neither of which will take a wired “timer”. Both use a simple IR remote focus and fire remotes they only cost about $2.

    The off the shelf interval timer unit is an easy way to go. I purchased a timer for about $20 on E-Bay. Oops only plugs in on other Sony models, but it has focus and fire outputs via a (3 contact) stereo plug.

    Would it be possible to fire an IR with that interval timer output via a simple circuit? If so, can someone email me a reference. Thank you.

    1. you could disassemble your IR remote and look at how the button works, if one side of the button connects to ground or the positive supply, then you can substitute the button with a transistor, and use a simple timer circuit or microcontroller to trigger it. in my pentax remote, the button connected two pins on the chip that controlled the remote, and employed a digital handshake, rather than a simple pull up / pull down. obviously pentax chose to to this to make it hard to hack the remote physically. they should have made the IR signal more complex, it was easy to reverse engineer.

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