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Though it's nice not to have to manually time exposures during colder weather it's also nice not to have to subject a laptop to the rigours of the environment. Commercial intervalometers (shutter timers) are available for about $130 from Canon. These are programmable and quite fancy, but still need modification in order to work with the Rebel series of cameras.
This latest in my never-ending series of 'things to build when the weather is lousy' is a simple, inexpensive intervalometer that will control your Rebel's shutter saving both your laptop and your pocketbook. It uses an LM556 dual timer chip and it will automatically take a series of ~35 second to ~6 minute exposures with your Rebel.
The 'dual' in the 556 means that there are two completely independant 555 timer chips on the single die, and this device uses both of them. The first timer is configured in bi-stable mode (this means that the output is stable in either the high or low state). Two buttons are provided which are connected to the 'trigger' and 'reset' pins of the first timer. Pushing the 'on' button drives the output high, pushing the 'off' button drives the output low. The output is connected directly to the 'reset' pin of the second 555 on the chip.
The second timer is configured as an astable multivibrator (not stable in either state) with separately adjustable 'on' and 'off' times. The on time is set through a 1M potentiometer. The 'off' time is set at about 13 seconds through a 33K ohm resistor. When the 'reset' pin is high the timer is running, when it is low the timer is stopped.
Two LEDs are provided as indicators. One tells us that the power (either a 9v battery or 12v from your mount) is on, and the second signifies that the shutter is open.
The camera is connected through a 4N26 (or equivalent) optocoupler to a 2.5mm stereo plug which plugs into the remote port. Shorting the tip to the sleeve of this plug trips the shutter. The device does exactly this by powering on/off the 4N26 to short the plug. If you already have a DSLR Focus compatible serial cable you can use it through a DB-9 male plug.
I needed a dial... so I first marked the case where each setting was for 1 to 7 minutes. Then I drew a diagram, scanned it into the computer and laid out a dial with the numbers and index marks. This was transferred to a PCB which I etched, trimmed and positioned. It works a treat.
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Parts List
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| The box I picked up is a 'no name' unit that has a compartment for a 9v battery and came with the battery pigtail. It cost me about $6. This was by far the most expensive part in the kit which came to a total of about $30 at a local electronic parts outlet. |
Also, the first exposure will be long. Normally the 556 changes state at 1/3 input voltage and 2/3 input voltage. On the first exposure the cap has to charge from essentially 0 to 2/3 input before the shutter closes. What I do is to set the timer at it's shortest exposure and trip the circuit. After LED number 2 turns off I dial in what I want for the rest of the exposures.
If you require exposure lengths that are exact and don't want to lose the first exposure (or fiddle around) then by all means spend $130 on a Canon TC-80. Or, you can spend a few dollars and hours on this.
To download a PhotoShop image with a layer for layout 1 that can be used as a board mask click here
To download a PhotoShop image with a layer for layout 2 that can be used as a board mask click here
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