Month: September 2009

I received a prompt response from Jim Rowe at Silicon Chip Magazine on the beam break trigger. Interestlingly the pulse was designed to be short to work with the time delay trigger kit but I didn’t have any success using the two together, maybe some of the components supplied in the kit were out of spec:

Greetings Mr Johnson,

You are correct in that the effective trigger pulse width from the June 2009 Beam Break Trigger will be only a little over 110us, as determined by the 10uF capacitor and the total resistance of 11.1k# in the charging circuit.
The pulse was actually made this short to prevent multiple triggering of the Time Delay Trigger published in the February 2009 issue. However if you want to use the Beam Break Trigger to trigger a camera directly, I imagine that the pulse width will be too narrow – as you have pointed out.

Your remedy of increasing the capacitor value from 10nF to 1uF is fine, but if this does not give sufficient lengthening of the trigger pulse for some cameras, the resistor from the gate of Q2 to ground can also be increased in value from its present value of 10k#. It could be increased to 22k#, 47k# or even 100k# if a much longer pulse is needed.

Thank you for your feedback, and I hope you find the projects useful.

Regards,
Jim Rowe

Recently I constructed the beam break trigger and photoflash trigger kits featured in Silicon Chip magazine. Both look good in general however I ran into an issue getting the beam break kit to work with the trigger because of the short duration of the output. I thought I’d share a letter I just wrote to Silicon Chip about the problem in case anyone else runs into the same problem before it’s published in print form:

After constructing the beam break trigger from the June 2009 issue I didn’t have any luck getting it to trigger a camera either directly or via the photoflash trigger kit. Unless I’m missing something doesn’t the 10nF coupling between Q1 and Q2 lead to a time constant of mere microseconds? I didn’t measure the timing before-hand but after doing a rough calculation I placed a 1uF cap over the 10nF which lead to a trigger time of somewhere in the order of 10mS and all was fine with the photoflash trigger kit. I left it at that because it’s my intention to use it with the trigger kit however readers should be aware that some cameras require a longer pulse on their external trigger to fire. For example my Canon EOS 450D seems to require a minimum duration of about 60mS in manual focus mode, presumably if the pulse is shorter than the normal shutter lag time it gets ignored. Other than that they are a pair of excellent projects and looking forward to exploring the possibilities they offer.