Some time ago, I first became interested in water drop photography after seeing some spectacular images on PBase and elsewhere.
I had a brief attempt at this using an eye dropper and a basin of water, trying to synchronise the splashes with the shutter by hand.
I failed miserably and almost gave up. Then I came across a web site written by David Hunt, in the Republic of Ireland, in which
he describes using a Raspberry Pi to control the water drops and the camera shutter:

http://www.davidhunt.ie/water-droplet-photography-with-raspberry-pi/

I invested in a Raspberry Pi and played around with this, building the interface described above, but, for a variety of reasons,
never got around to completing the project until very recently! (I did go through several versions of the Pi during the course
of this project and am currently using version 4, perhaps the most powerful version, to date. Most of the time, I tend to use
this as an internet radio while I'm working on my desktop!)

(There are now commercially available kits which do, for a price (!), what this Raspberry Pi system does, and more perhaps,
but to my mind that’s almost cheating – someone else has done all the work and all the operator is doing is pressing a button.
(Also, the commercial kits don't play Internet radio!) For me, half the fun – and satisfaction – is making the kit in the first place!
Even so, I didn’t design this, but I did have fun putting it all together, and brushing up on my soldering and programming skills
– I spent a lifetime working with electronics and programming in Fortran, as a research physicist, so this was a novel way of
using those rusty old skills!)

The sequence of events for these images is as follows, for those not familiar with the process: a solenoid valve (the heart of the
system) opens and closes to release a small drop of water, then a short time later it repeats to release a second drop. The first
drop hits the surface of the water in the tray below and it then "bounces" back up and starts to rise. At the same time, the second
drop falls and crashes into the first drop as it rises, creating the splash. At this point, the camera is triggered to take the photo.

There are thus 4 parameters to control - the size of the first water drop (which depends on the length of time the valve is open),
the time period to the second drop, the size of the second drop and the delay before firing the shutter. These parameters are
controlled by the software running on the Raspberry Pi, and getting these all "correct" is a matter of trial and error.

So, at long last, here are a few examples of my early attempts at water drop photography! Plain water turns out to be quite tricky
to work with, and more successful results are usually obtained using fluids with somewhat higher viscosities. Accordingly, my first
attempts were done with water thickened slightly with xanthan gum (something like 1/3 teaspoon per litre of water).