Canon EOS Remote Intervalometer

To create a time lapse video, you need to take a bunch of still images and stuff them into a video editor. The trick is you don't want to have to stand there with a stopwatch for hours, snapping hundreds of photos. Thus the need for an intervalometer - a device which repeatedly trips the camera's shutter. Some cameras already have this feature, and there's custom firmware such as Magic Lantern or the Canon Hack Development Kit which implement the feature, but I wanted to have the opportunity to experiment a little. My main goal is to make videos of the Milky Way as it rotates across the sky. On my camera (a Rebel SL1), I use a 15 second exposure at ISO 12800, and then the camera takes about 20 seconds to process each image. For this reason, I decided to start with a 60 second interval. At this interval, every hour in real-time compresses down to two seconds of video. 

My camera uses an infrared remote, which is ideal, because there's less chance of bumping the camera, causing a shaky image. I have a remote like this. According to various sources on the web, the remote triggers the camera by sending out two 32 kHz pulse trains. If the pulse trains are 5.35 mS apart, the camera triggers with a two second delay accompanied by beeping. If the pulse trains are 7.35 mS apart, the camera triggers immediately. To confirm that this is how it works, I disassembled a photo-interrupter, and removed the phototransistor. I then connected it to a 5 volt source through a 1 kOhm resistor. Because the frequencies involved are rather low, I was able to use my DSO Shell oscilloscope, which has a max speed of only 10 uS per division. 

Sure enough, there were two pulse trains at 32 KHz. I set an Arduino up to drive a 950 um LED at 32 kHz every 5.35 mS and to my surprise it only worked if I waved it all around the camera. If I pointed it directly at the receiver in the front of the camera's hand grip, it didn't work at all. The signal looked good...

Going back to the Amazon remote, I noticed that even if you held the button down, it only sent two pulses trains. I had though that if I sent more pulse trains, the remote would be more reliable. Since that wasn't the case, I added a button to the project that allowed only two pulse trains per button-push. Now it worked reliably. 

One other improvement I added, was that I wired the infrared LED in parallel with the Arduino Nano's internal LED on pin 13. That way you can tell when the LED is on. There's another way you can tell, though. Look at the LED with an old or inexpensive webcam. In the image below, you can see the infrared LED glowing white when viewed through my webcam.

 

This infrared-viewing trick used to work with the camera in my old Palm Pilot, but it doesn't work with my  iPhone. I assume it's because Apple added an infrared filter to the higher quality iPhone camera.

The next step was to make it send two pulse trains every 60 seconds. That was easy but I wanted a count-down timer so I'd be able to tell if the intervalometer was running, and to see how long until the next exposure. In my junk box I had three HP 5082-7340 LED display modules from the 1970s. These displays have nice-looking numbers compared to most seven-segment displays and have on-board memory so your microcontroller doesn't have to tie up processing cycles doing a multiplexed driver scheme. In the days when microcontrollers were expensive these displays were a great idea. Now they're just nostalgic - but I was surprised to see some vendors asking as much as $20 on Ebay, especially since you can get an OLED graphical module for less than $10 these days. 

Here's how the current project looks. Please ignore my ugly wiring! Whenever I try cutting leads to some exact length, they always come out either slightly too long or worse yet, slightly too short. I really need to make some kind of template. So for now, I just use longer jumpers and let the wires go everywhere! 

I have the first digit displaying the letter A, just because it can. Maybe that will be some kind of mode designator in the future. One thing I don't like about these LED displays is that they get kind of warm. That's probably causing excessive battery drain when I'm powering it that way. In the future I may use the display's blanking control as a dimmer so it doesn't use so much juice.

Another thing I want to change is the brightness of the power LED on the Nano. It's so distracting! Rather than attempting to change the microscopic resistor in the circuit, I may just put some white paint over the LED!

Finally another feature I'd like to add is a start/stop button and a way to adjust the interval.

You can find the Arduino source code here.