A Camera Intervalometer

Hawai'i is an island of amazing clouds. As the wind sweeps around the dramatic high altitude topography of the island it creates a dramatic cloudscape. The resulting scenes are often the target of my camera, but the motion is hard to see in a single frame or a short segment of video. Time lapse is the answer, allowing the fascinating flow to be seen in the resulting video.

There are so many targets available for time lapse photography, from clouds to tides or simply the day to day activities around us. Since I have had the Canon G11 I have been unable to capture time lapse. The G11 lost a very nice feature found on the G9, an intervalometer mode when shooting movies. The earlier model created movies with 1 or 2 second delays between frames, allowing nice time lapse sequences to be filmed. The G11 does have one feature that compensates, a connector for an external shutter release. Combine this connector with a intervalometer and the camera would again be usable for time lapse work. Better still, the still frames can be full resolution and shot with full manual exposure control, the resulting time lapse could be assembled into very nice HD video.

I have a programmable shutter release for my Canon 20D, the Canon TC-80N3. A nice device, but it has always frustrated me. It does not display the remaining number of exposures in a sequence and the backlight shuts off after a few seconds meaning I have to use a flashlight near the exposing camera to read the display in the dark, or risk jiggling the camera fumbling for the backlight button. I decided that if I build my own I can design it with just the features I want.

The camera shutter release connector is simple enough, a focus contact equivalent to a half press of the shutter button. An expose contact equivalent to a full press of the shutter button. The details of how to use these contacts are widely available on the internet, with example designs from several other hackers. Both of these contacts are used in my design, a pair of opto-isolators designed to actuate each contact. The focus contact is closed four seconds prior to the exposure to allow the camera to focus if necessary.

The design is simple, a PIC16F873 microntroller and an LCD display form the heart of the device. I have a lot of code around for the PIC, and know the processor well. This allows the coding to proceed quickly and with fewer errors. The addition of the LCD display is new for me and it took some work to develop robust control routines. Not complaining here, I enjoyed the coding.

The device runs on two AA cells and consumes a maximum of 11mA with the backlight on. Power management is incorporated with the display powered off and the processor dropping into sleep after 30sec of inactivity. Even at full load this should provide over 250 hours of operation from standard AA batteries. An internal 3V regulator is available to take power from an external source allowing continuous operation for even longer periods.

Care was taken to produce accurate timing as the intervalometer cycles from delay, to expose to inter-frame delay. A master clock counts seconds and each phase transition takes place on a second mark. If shooting short exposures in auto-exposure with a five second interval, each frame will trigger exactly five seconds apart, despite whatever time it takes the camera to expose and store each frame. Camera control was carefully tested with a digital oscilloscope to insure no glitches exists and timing is correct.

The resulting intervalometer is now operational. There are a few features that I wish to add in the short term, but there always are for this sort of project. Expanding the frame counter to 16 bits is probably the first on the list. I included a number of extra contacts in the external connector, a pair general I/O lines and a serial port. I hope that one of my next projects will be a pan-tilt camera platform. This simple intervalometer will then become the controller that sequences motion with the exposures... shoot, move, shoot again... all I need is a few more lines of code to accomplish some sophisticated sequencing.

A nine pin D-Sub connector is used to provide a rugged connection, extra contacts for the extra features and a lockable connection. A very basic serial port is executed using a two transistor level shifter. Nothing new here, another circuit commonly published across the web.

Various tasks are configured through use of different cables. The first cable is simple a DSub 9 at one end. While the camera connector is a 2.5mm stereo plug for the Canon G11. There is no reason that the intervalometer can only be used with the Canon G11. With the correct cable the device could control any camera with an electronic external shutter release.

While I do have a number of plans for improvements, they will have to wait. I have a lot of ideas for video to be shot with this setup, with the final testing complete it is time to start taking time lapse!