iesmith.net photography

In May of 2009, I successfully submitted a portfolio of ten images for an LRPS distinction. In an attempt to show the panel I wasn't a landscape photography 'one trick pony', I included two of the perhaps three genuinely successful 'studio' photographs I'd taken at that point. They were reasonably well received, and the judging panel commented that it was nice to see I "stayed indoors, from time to time."

I have to admit, the judges had a point. I love the outdoors, and so it's natural that my photography leans heavily towards landscapes. I've often wished I was more accomplished at studio photography however, if for no better reason than having the ability to occationally distance myself from the fickle British weather. It's ironic then, that a project that began as a way to stay dry during a British summer should involve me getting as quite as wet as I have photographing my chosen subject for this little project: water drops.

The Arduino Microcontroller - Is it waterproof?

I'd always been drawn to time-lapse and macro photography, and it seems that the obiquitous water-drops are a common first step into this strange and wonderful photographic world. In researching it further however, it quite quickly became apparent that there would be more to this project that met the eye; the action takes place in a fraction of a second in a tiny space no more than 18 inches or so from your camera lens. Presented with these challenges, it seemed to me (and undoubtedly many before me) that there would be two ways you could go about photographing these tiny splashes. The first is simply to fix up your camera on a tripod, set up a reasonably predictable source of water drops and fire away at it. There are many people who have achieved great success with this approach, however not being blessed with the greatest amount of patience, I wanted to increase my hit rate. It's for this reason that I went for the second approach; to control as many of the variables as possible using any and all tricks I could put my mind to.

The challenge would therefore be to build, find or scrounge a detector that would be able to detect the moment a falling water drop began it's descent, and then to wait a configurable period of time before triggering the camera's flash and/or shutter - in other words a photogate/delay timer circuit. There are kits available such as those from HiViz.com, however I felt that the delay timers on these circuits were a little less controllable than I would like, and with my programming skills being somewhat better than my electronics skills, I decided to build a programmable circuit based on the Arduino Microcontroller. Additionally, controlling the delay timer from a PC or laptop would give me millisecond accurate control, and it would be much more repeatable than the somewhat vague screwdriver-adjusted potentiometer employed by the HiViz kits.

I chose the Arduino as it's a wonderful little platform for rapidly developing solutions such as this, and I found that with just a little electronics knowledge I was able to get into building and designing my own circuits quite quickly. You'll soon see that I quite quickly got beyond the simple litle flash controller I'd originally planned on building.

Before we get to the good bits though - a note on safety. Be careful, please! Flash units have some very high voltages, so take all due care and attention. I take no responsibility for burned out flash units, smouldering Arduinos, fried cameras and melted retinas because you discharged a flash into your eyes. Magic smoke is a crucial component of any electrical device, and once it escapes it can be very expensive to have it put back in again! I'd also warn you about soldering irons too, but since I accidentally burn myself with one on a semi-regular basis, I'd feel somewhat hypocritical. That said though, they're hot - be careful which end you pick up!

Required Parts - A Shopping List

First, I'll go over the parts required to build your own circuit. I've linked to sites where you can buy these components off the shelf, but you may well find there are parts available elsewhere at a lower price. It's always worth shopping around if you have the time, but even so, the parts listed below should set you back no more than about £30.

• 1x Arduino Microcontroller. I used a Duemilanove, but many of the other models will also work.
• 1x Arduino Prototype Shield or Breadboard.
• 2x 4N35 or 4N25 Opto-isolators.
• 1x GP1A57HRJ00F Photo Interrupter & Breakout Board.
• 3x 1K Ohm Resistors.
• 1x 220 Ohm Resistor.
• 1x Momentary Pushbutton Switch. Note: I used a Combined LED Switch to combine both the arming switch and the indicator LED, but a seperate LED & switch works equally well.
• Up to 2x mono 3.5mm jack socket connectors and plugs (optional). I use these as input/output connectors, which is particularly useful if your flash has a 3.5mm jack trigger input! Note: you'll need an additional stereo connector too, if you decide to hook up your Photo Interrupter in this way also.
• 1x 100mm x 80mm x 40mm Project Box (optional).
• 1x Standard USB Cable (printer type).

Don't be shy about substituting parts if you know what you're doing... I'm by no means an electronics expert, but I have tested the parts used above quite extensively now, and I do at least know they work.

How it Works

The Arduino Photogate is actually a relatively simple circuit. As a relative beginner to electronics myself, I found it easier to understand than the HiViz kits I had worked with previously. This may simply be a product of my designing it myself, however I do believe that it's modular design helps in this regard.

If you look to the circuit diagram to the right (click to enlarge) you'll see that it can be broken down into a number of discrete sections:

• The detector. To the left of the diagram, there is an IR LED and photodiode hidden inside the GP1A57HRJ00F. These components simply detect when a drop of water passes between the two 'arms' of the detector and breaks the infrared beam.
• The shutter trigger. Once the drop has broken the infrared beam, the circuit sends a signal to the rightmost opto-isolator (see circuit diagram), which will then open the camera's shutter - which should have shutter speed set on the 'bulb' setting. This step is strictly optional, and you can disregard this part of the circuit entirely if you're willing to work in a darkened room and rely on your flash to capture the action.
• The timer. The timer is built into the Arduino Microcontroller, and simply waits the period of time (usually milliseconds) that you've programmed into it via the USB cable until the drop reaches the water container and makes a splash.
• The flash trigger. Once the drop has reached the water and made a splash (or more accurately, when the programmed delay period has been reached) the circuit then sends a signal to the leftmost optoisolator to close the output circuit and fire the flash.
• If you're using the shutter trigger, the circuit will then close the camera's shutter.
• The arm switch. Once the flash has fired and the shutter closed, the Arduino will then disarm the trigger, which will stop the flash or shutter from firing again until such time as you're pressed the contact switch. The LED will turn off, indicating that the circuit is disarmed. This will prevent the flash from firing too quickly should any stray water short the detector, which could burn out your flash. You'll then need to press the contact switch to take another photograph.

You can download the circuit diagram in PDF format here.