Problem with activating bulb mode on Canon 40D


I have built a camera controller and I am having issues with activating bulb mode on the camera.
Normal shutter activation works OK.

The controller should follow the following process; open shutter, wait for a sensor to trigger, activate flash, close shutter.
I have this working with a timed exposure (for example 3 seconds) but cannot get it to work with bulb mode.

On the 40D, bulb mode is active while the shutter release is pressed. It works the same way when using a manual shutter release cable. The release cable is a simple contact switch and the shutter is open while ever you are holding the button down.

I have the camera connected to the Arduino via an opto isolator and I had thought that keeping the pin high would keep the shutter open but this is not happening. The shutter is triggering but closing very quickly. I have tested the trigger by using a LED circuit and the LED is lit exactly when it should be so the timings on the pin are OK.

Any suggestion would be greatly appreciated.

The shutter button on the camera (and on the remote) is using two switches which is swiched in succession. Without both, bulb mode won't function.

You need two opto-isolators.

// Per.


Added the second opto. Now working like a charm. Thank you very very much.