This is another of my pre-Instructables projects. Again it lacks some documentation but still I think it's a nice one to share.
Taking a photo of a water drop splashing on a water surface isn't too difficult - if you invest a little time. And the results are quite stunning. There are lots of people driving this to some excess or doing it professionally. This was not my intention. I just wanted to explore how difficult it is to catch this splash-moment.
Edit: I have added the renamemetogif file with a sequence of drops (as suggested in the comments). You need to download and do as the name suggests since the build-in view does not show animation in gifs.
Step 1: Catching the Moment
The first thing to do was to recognize the single drop falling from a certain height, ready the camera, wait a short amount of time, flash and close the shutter. This could be controlled by my Arduino. It just needed the input about the drop passing a point, a trigger for the flash and another for the camera.
I simply mounted a yellow LED (because I had one lying around) and a LDR (light dependent resistor; because I had a dozen of them lying around) opposing on a 3 cm PVC tube in holes that fit. A drop created from a syringe falling down the tube had to pass the light/resistor gate resulting in a change of the LDR resistance. A few tests showed that this worked - oh kay - so to say. Definitely a laser from a laser pointer would have produced much better results. But for my tests I decided to leave it this way. I just shortened the PVC tube later to just hold the light gate.
Flashing the light
The next step needed some watching on eBay. I shot a flash for about 6€. That was simply perfect. Instead of the 4 AA batteries I connected my lab power supply. The trigger only needed a simple transistor driven by the Arduino. I opened the flash casing and soldered two wires for the trigger. Just to find out later that there was a phone jack which had the two pins already connected. Anyhow, my Arduino was able to trigger the flash - even multiple times per second depending on the needed strength (so having a possible stroboscope!).
Having said strength, opening the case was not that fruitless. The sensor which shuts the flash after enough light has been shed, had a loose cable. So that was fixed on the go.
Pressing the trigger
Operating the camera to open and close the shutter at the right time was more a challenge. I have a very old Casio where I once made a frame to trigger it with a servo. This worked quite nicely but for this project I needed some better camera. So I borrowed my son's Canon. Not a professional device too but more than good enough. Most of the Canon cameras can be hacked to be remote controlled via USB power. Find out more at CHDK (Canon Hack Development Kit). Basically you load a new firmware temporarily into the camera and get tons of new features. I just needed the remote operation via USB. I chose the mode where the first trigger readies the camera (setting focus etc.) and the second actually opens the shutter for the preset time.
Putting the basics together
Now, when the Arduino detects the falling drop (which worked in about 30% of the cases) it sent the first ready signal to the camera. A short delay later the shutter was opened with the second trigger. And finally the flash was triggered to take the photo. This way I got my first falling drops banned on camera chips.
Step 2: More Drips
Since taking photos this way was very cumbersome, I decided to add a motor-driven syringe to produce the drips. Luckily I have a set of Fischer Technik which is ideal to build prototypes. With a few bricks and cog wheels I created a syringe press that allowed to create lots of drops rather precisely. But of course the manual way was not what I was after. I needed to got for "The Full Monty".
Step 3: The Fully Automatic DPAPT (drop-producer-and-picture-taker)
So here is the complete setup. The lab power supply is just used for the flash light. This and the camera are on a small mount that came with the flash. I used some aluminum foil as diffusor for the flash. The mount is fixed on my Dremel vise which allows a nice positioning towards the target. The target is a small egg cup made of glass and filled with water. I placed a piece of white paper behind to get a better light. Unfortunately paper soaks up the drips that splash out and are visible later. Better would be some white plastics you could clean easily.
A bit higer on a stool I placed the rest of the setup clamped to a wooden plank. The syringe press now has a stepper motor driving it. It would turn the motor until a drop has been presses out of the hose and been detected by the photo gate. Now the press motor is stopped and the before mentioned photo process issued. First I had a lot of bad photos until I discovered that the camera needs quite some time to process the photo before another one can be taken. Being too hasty results in bad/black photos. So after a short pause the drop creation is continued until a certain amount of turns of the motor. The motor then turns backward these turns and the syringe can be reloaded (manually). So the only thing to do was: press the start button, wait for all drops to be fallen, clean the camera/spilled water and eventually unload the camera chip to my computer where I had to revisit the photos for good and bad (not so easy).
The schematic is rather simple, so I just attach a picture of it. The same goes almost for the sketch. Initially it waits for the button to be pressed. A short press just produces a single drip and a long press will repeat until the syringe is empty (number of motor turns). The timing values were found empirically and need to be adapted for each setup. It's quite interesting to modify the actual point in time to see different splash-phases.
Step 4: The Last Drop
Yep. That was one of my last photos. It was fun but I'm not addicted. Maybe with lessons learned I will create a new machine in the future. I also know that it's fun to use milk and color instead of simple water. I did not try that, though.
Once again apologies for missing parts and especially the video with the operating machine. Maybe with the next one :-)