Tinker time again

I've discovered that this pandemic has given me lots of time to "tinker". Some people like to do puzzles, some like to read, some like to watch tv. I like to build things, either out of wood in my wood shop, or using electronics and microcontrollers. This time it's the latter. I wanted to take pictures of water droplets colliding. You've probably seen them before, they look like water mushrooms. In order to accomplish this, two water drops need to fall in sequence with precise timing so that they collide at the perfect moment. Then, with the camera shutter open, the flash is triggered to freeze the action. A flash can freeze action to 1/27000 of a second! To make water droplets fall at precise times, a solenoid driven water valve is used. The valve is fed by gravity from a reservoir (root beer bottle). To control the solenoid, the camera and the flash so that they would activate at the proper timing, I used an Arduino UNO. This is a small programmable microcontroller similar to a Raspberry Pi but simpler. I used it to drive transistors, optocouplers and a MOSFET (for the 12v solenoid) which I wired up on a blank PCB. I wrote a simple program using the Arduino IDE (it uses C++) which allowed me to adjust the timing parameters via a USB connection to my MacBook Air. It takes a lot of tries to get the timing right, even after measuring the height and using basic physics, t=sqrt(16/h). I'm still in the process of honing in on the right numbers, but here are some photos of my initial results. More photos will be posted in my photo gallery section soon.