Step 3: The Circuit

Picture of The Circuit
circuit copy.jpg
At the bottom you'll see a link to a pdf containing the schematic.

To trigger your CHDK enabled camera we'll be using the USB remote function. In this case we have to use it via the 'syncable' method, which is lightning fast compared to the normal USB remote.

The syncable remote also operates differently. It triggers the camera on the falling edge instead of the rising edge of the 5-volt signal. When the camera detects the 5 volt USB signal, it gets ready to take a shot, waiting for the voltage to fall to zero.

There are high-speed camera trigger circuits floating around the 'net but I couldn't find any for syncable USB. So I cobbled together the circuit below.

It uses a 556 timer IC, an inverter, a photoresistor and some caps and resistors.

The dollar store had a USB cable identical to the one my camera uses. I lobbed one end off of it, instead of wrecking the one that came with my camera.

A 5-volt power supply is needed to power the circuit. If you don't have one, pick up a cheap USB charger, or add a 7805 voltage regulator to the circuit.

The photoresistor is not on the circuit board; it's mounted on a small piece of perf board at the end of a short cable. Glue some magnets onto the back for easy alignment with the laser.

The circuit should be built first on a bread-board and tested. Once you're sure everything is working then either etch a circuit board or use a prototype board like I did. Or just continue using the circuit on the bread-board.

NOTE: OCT 2nd, 2009 There was a huge mistake in the schematic that instructable member toxoof pointed out. The PDF has been corrected.

OCT 19, 2009:  another error has been found in schematic. Arrrggggg!

July 30, 2010: Schematic revised to use photoresistor

Download the pdf here:  Schematic
Frivolous Engineering (author) 2 years ago
Hey Redrua:
1: Photo-resistors are much easier to location/purchase, but they aren't as responsive/fast as diodes. It's your choice what to use.

2. The type of cap doesn't matter (except for price) as long as the value is correct. What type of cap you use depends on price/availability.

3. 220K pots should work. Multi-turn one are preferable because you have finer adjustment compared to a single-turn pot.

Hope this answers your question!
redrua2 years ago
I have some questions.
First question is: In step 3 you told that schematic revised for photo resistor. I went to a electronic component store bought everything but the photodiode. Then I checked the schematic and saw that you used photodiode (sharp BS120R0F) in it. Should I use my photo resistor instead of photodiode or should I buy a photodiode?

Second question is: I am not a electronic tech guy or something like that. I am just wondering why you used differend type of caps? (ceramic, metal film, electroylitic) when I was at component store they told me that they don’t have ceramic ones. I thought that they all are caps and told them ok give me what you have. Their capacity are same. Now I am not sure about what I did. Will this cause a problem or not?

Third question is : I get trimpots but they do not look like the ones on your photo and they are 220K ( they have only these). Is it ok?

As I said I am not a electronic guy. I asked these questions to people working at shop but they said they can not give advice because they don’t want to be responsible. And that store is the only one in this city. I don’t care about the prices of the components (a few bucks) or price of camera (it is toy for my kid, bought for a few bucks from someone), I just want to take these photos. I just want to do it right. I will be glad if you help me.
drivera14 years ago
harshads5 years ago
i have a sony cyber-shot camera and less likely to obtain a canon.......please post the method with a sony cyber-shot camera.
i will be very gratefull
natsfr harshads5 years ago
I just just did it with an Alpha 700 from sony,
give me your cybershot model, maybe it's the same connector for remote command :)

(I'll write a little how to for the alpha)
lfcrule25 years ago
 You think it's possible to modify a shutter remote with this so that I can trigger my film slr?
dr_3soma5 years ago
Dear\ SaskView Very Nice instrutable but i'm asking about the circute and the laser trigger could be installed with flash (Professional FLASH) so the laser trigger will release the flash instead of camera and the trigger could be suitable for DSLR Professional Cameras like Nikon D80, Waiting for your reply and thanks again Essam
txoof5 years ago
I would like to try to hack this to work with my Olympus E510. I built a remote shutter release that basically just brings two of the pins in the jack to ground and that fires off the shutter. Can you offer any advice as to how I could modify your circuit to do the same thing? I'm not terribly savvy when it comes to anything more complex than a super basic circuit like the one I built for my shutter release, but it seems like I should be able to either make a relay (seems slow) or something that does the same job to make this work for my camera.
Any ideas would be greatly appreciated!

Link to my shutter release: http://www.instructables.com/id/Olympus-Evolt-E510-Remote-Cable-Release-Version-2/
Thav5 years ago
Pretty neat. If you're worried about damage to the USB connector on the camera you can add two schottky diodes to shunt away transient voltages from the USB connector. It's probably not necessary with this circuit since it is pretty simple but it's an extra precaution. You would want to place the diodes as close to the connector/cable as possible. If that's far away from your main circuit, consider adding a 0.1uF ceramic cap from +5V to ground near the USB connector.