Introduction: Laser Triggered High-Speed Photography

About: Frivolous Engineering is the end result of a hobby that got out of hand.

In order to consistently photograph something like milk drops the usual method uses a high-end camera ($500 and up), Speedlite flash ($300 and up) and an optical electronic delayed flash trigger ($120 and up).

There are lots of DIY circuits for this purpose, but they still require a good camera and a high-end flash unit.

And you have to manually open the shutter requiring the photo to be taken in a darkened room.

Here's how you can consistently take the same photos with an simple circuit, inexpensive point and shoot camera, no additional flash unit, all without fumbling around in the dark.

The video above shows the ease of use of this rig and some of the better splashes of the hundreds that I've captured.

I've concentrated on milk drops, but this can be used for many different things. The separation between the laser and the detector could be hundreds of feet apart, or bouncing off mirrors...

Thanks, and have fun spilling milk!

-Brett @ SaskView

Step 1: Materials

I got the following at my local Dollar store (each item was actually $1.25: talk about misleading advertising!)

Laser pointer
Door chime
USB Cable
Shelf brackets
Self-Adhesive backed Velcro
Small picture frame (for the plate glass insert)
Eye drops (for the dropper bottle. I poured out the contents as I believe anything
purchased at a dollar store should never be applied to one's eyeballs!)

Here's what you'll need for the circuit (I don't think your local dollar store will have these so you might try an electronics distributor like Digi-Key):

Part/ValueDigi-Key Part #

4  .01 uF 50V metal film CapsP4513-ND
3  1.0 uF 50V Ceramic Caps
1  10 uF 35V Electrolytic Cap
1  1K Ohms 1/4 W resistor1.0KQBK-ND
1  22K Ohms 1/4 W resistor22KQBK-ND
2  120 Ohms 1/4 W resistors120KQBK-ND
2  200 K Ohms .5W Multi-turn PotsCT94EW204-ND
1 Green LEDP14228-ND
1 Red LEDP14224-ND
1 LM556CN timer IC
1 7404 inverter IC568-2921-5-ND
1 Photodiode                                                                              PNZ300F-ND

Please note that the schematic has been revised to use new photodiode.

Step 2: The Camera

You'll need a Canon camera because we're going to temporarily modify its firmware using the Canon Hacking Development Kit. CHDK is loaded onto the memory card inside the camera, allowing us to override most of the camera's functions, turning a cheap point and shoot into a highly adjustable way-cool time freezer.

Currently there are 47 Canon cameras that CHDK will work with. Check the CHDK Wiki to see a list of them. I'm using an A470 that I purchased new for about a hundred bucks.

Download the correct CHDK build for your camera from the CHDK auto build server and install it on your camera's memory card.

A great tutorial to help you get CHDK running on your camera can be found here.

Installing CHDK didn't harm my camera, and it's temporary. I can revert back to the original firmware simply by turning the camera off and restarting it without CHDK.

Of course I can't guarantee you won't blow up your camera by attaching home-made electronics to it. Do so at your own risk!

Step 3: The Circuit

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

Step 4: The Laser

The laser pointer has a momentary switch but I wanted a slide switch that would allow the laser to remain on without me holding the button.

The Dollar store magnetic door chime not only had the slide switch that I wanted, but also it used the same kind and number of batteries that the laser does. This was cheaper than buying just a switch from an electronics supplier.

I removed the tiny circuit board from the door chime and installed the working guts of the laser in its place using the chime's switch and battery holder.

You don't have to go to this extreme if you don't want to. Just use a rubber band rapped around the laser pointer to keep it turned on.

Like the photodiode, I hot-melt glued some magnets on the back.

Step 5: The Drop Rig

Below is a photo of my setup.

Some pieces of wood and some steel shelf brackets clamped to a TV tray.

The laser is mounted with the magnets on one of the brackets, and the photodiode on the other. In between and slightly above I've velcro'd the eye dropper bottle filled with milk.

Step 6: CHDK Settings: Enabling Synchable Remote

In order for the USB cable remote to work, you have to enable it.

With CHDK installed on your camera go into the Main Menu and at the very bottom you'll see Miscellaneous stuff. Enter that menu and at the very bottom of it you'll find the Remote parameters menu. In that menu set Enable Remote [.]

Make sure there is a dot inside the square brackets, meaning it's enabled.

Below that is Enable Synchable Remote. Enable it.
Next is Enable Synch, enable this too.

Also on this screen are settings for synch delay. They didn't work for me, and that's another reason I built the delay circuit.

Step 7: CHDK Settings: Extra Photo Operations

Now go into the Extra Photo Operations menu at the top of the main menu and set:

Disable Overrides [disable]
Include AutoIso & Bracketi [.]
Override shutter speed [1/10000]
Value factor [1]
Shutterspeed emun type [Ev Step]
Override aperture [5.03]
Override Subj. Dist. V [350]
Value factor [1]
Override ISO value [80]
Value factor [1]
Force manual flash [.]
Power of flash [1]

In order to get the right exposure you will have to adjust the aperture, ISO, and flash power settings.

Lower aperture numbers will brighten the shot, higher numbers will darken the shot.

Keep in mind that the higher power of flash, the longer the flash's duration will be. You will want to use the lowest flash power that provides sufficient exposure. Flash power of zero is very feeble and you may need to use 1.

For the ISO you will want to use a low ISO value because higher ISO's cause more noise and the resulting pictures look grainy. The overall ISO is the value times the factor. Factor can be 1, 10 or 100 giving you an ISO anywhere between 0 and around 32000. Keep in mind that ISO's lower than 40 or higher than 800 are most likely beyond what the camera can actually achieve.

The CHDK wiki says it best:
Just because you can set an override shutter-speed, f/stop or ISO sensitivity on your camera with CHDK, it doesn't mean your camera can actually do that setting. Be sure you have tested to make sure that extreme setting is actually making a difference in your resulting images.

Override Subj. Dist. is supposed to override the auto-focus forcing the camera to focus at a desired distance. I can't seem to get this to work. I'm not sure if I'm doing something wrong, or if there is a bug. My work-around is when the camera is being armed it will auto-focus and I put my finger at the point where the drop is going to land, letting the camera auto-focus there.

Step 8: Adjusting the Camera Settings

Normally you would be triggering an external flash, while the shutter is open using a cable release with the camera in 'bulb' mode. Once the flash goes off, you let the shutter close. This requires the room to be darken because the shutter will be open for many seconds.

In this setup you can have the room lights on because the flash and shutter are triggered at the same time, and the exposure is set for 1/10,000th of a second.

Before we hook the camera up to the trigger circuit we first adjust it's settings, manually taking pictures until we get the exposure correct.

Mount your camera on a tripod and place a stationary test object right where the drop is going to land. Frame the test object, and adjust zoom to your liking. Use the macro setting if your camera is close enough to do so.

Keep in mind that you will most likely get milk splashed onto your camera and lens, so the Dollar Store glass plate should be placed in front of the lens to prevent this. If the glass plate is in front of the flash it may reflect back into the lens, causing unwanted glare.

Now take a test shot and revue how it turned out. If the shot isn't properly exposed adjust the exposure, flash and ISO until it is.

You can also adjust the shutter speed, but keep in mind that it's mostly the flash that's freezing the action. I set the shutter speed to 1/10000 of a second and left it alone.

On my A470 aperture override is not available. In its place is ND Filter State. ND stands for Neutral Density filter. Some cameras don't have an iris, but instead have a filter to adjust how much light enters the camera. If your camera has this instead of aperture override you won't have as much control over exposure because there are only three settings: [In], [Out] and [Off].

Step 9: Adjusting the Circuit

With your drop rig in place mount the photoresistor to one of the steel brackets and the laser on the other one. Adjust the position of the laser so that the droplets fall through the beam. Adjust the position of the photoresistor so that it's illuminated with the laser.

Power up the circuit. LED1 will light up, indicating power.

Before we begin using the eye-dropper, we should set the photoresistor's sensitivity using VR1. Momentarily interrupt the beam. LED2 should blink indicating the circuit has tripped.

Adjust the sensitivity so the circuit triggers consistently. You may find ambient room light is interfering with the circuit, either preventing or causing false triggering, so you may need to dim the room lights, or mount a shade around the photoresistor.

Make sure that the delay potentiometer is set somewhere around the middle. If it's set to the very end of it's limit, the circuit won't work.

Once the circuit is working, power it down and plug the USB cable into your camera.

Turn on your Camera with CHDK running, then power-up the circuit. A 5-volt signal will be fed to the camera. Sensing that signal, the camera will pre-focus, and then it's LCD viewfinder will blank. The camera is now armed and ready, waiting for the 5 volt signal to fall to zero.

Interrupt the laser beam, and after a very short delay the camera will take a high-speed flash photo.

Interrupting the beam a second time will re-arm the camera for it's next shot. Once the circuit is working, interrupting the beam alternates between arming the camera, and tripping the shutter.

Now it's time to start spilling milk. All that's needed is to dial in the proper amount of delay.

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