Alright, so I’ve been meaning to share this little weekend project I cooked up. The weather was getting pretty warm, and I figured, why not build something fun, maybe a bit silly? That’s how the idea for an automatic squirt gun popped into my head. Sounded like a good way to mess around with some electronics and maybe keep the neighbor's cat out of my flowerbeds, you know?

Getting Started: The Parts Pile

First thing I did was rummage through my parts bins and order a few bits. I knew I'd need a small water pump. I found one of those little 12V diaphragm pumps online, the kind people use for small fountains or RV sinks. Cheap and cheerful. Then, for the "automatic" part, a PIR motion sensor seemed like the obvious choice. Had a couple of those lying around from another project that never quite got off the ground.

And of course, a brain for the operation. I grabbed an Arduino Uno – it’s my usual go-to for these quick-and-dirty builds. Simple, plenty of pins, and I know my way around it. To switch the pump on and off without frying the Arduino, a relay module was essential. The pump draws way more current than an Arduino pin can handle directly.

• A 12V mini water pump
• A standard PIR motion sensor
• An Arduino Uno
• A single channel relay module
• Some flexible tubing (like for fish tank air pumps)
• An old plastic water bottle for the reservoir
• A 12V power adapter (had one from an old router)
• Jumper wires, breadboard for initial testing

I figured this would be a piece of cake. Hook it all up, write a few lines of code. Done in an afternoon. Famous last words, as usual.

The First Attempt: More of a Dribble, Really

So, I got everything on the breadboard. PIR sensor to an input pin, relay control to an output pin, pump wired through the relay. The code was dead simple: if the PIR sensor goes HIGH, turn the relay on for a second, then off. Pump runs, water squirts. Easy, right?

Well, not quite. The pump hummed to life, sure, but the "squirt" was more of a pathetic dribble out the end of the tube. Not exactly intimidating. And aiming it? The tube just kind of flopped wherever it wanted. Plus, the PIR sensor was being a pain. Sometimes it would trigger if a butterfly flew past, other times a whole person could walk by and nothing. This wasn't going to scare off any cats, let alone be fun.

Making it Actually Squirt: Iteration Time

Okay, clearly, I needed a proper nozzle. I remembered an old Windex bottle in the recycling. I salvaged the nozzle from that, managed to jam the tubing onto it. Instant improvement! Now I had something resembling a jet of water. Progress!

Next, aiming. The floppy tube wasn't cutting it. I found a small block of wood and used a couple of zip ties to secure the nozzle and a section of the tube to it. Still pretty crude, but at least it pointed roughly in one direction. I also spent a good half hour fiddling with the little potentiometers on the PIR sensor to adjust the sensitivity and the on-time. Lots of waving my hand in front of it, moving further away, closer, trying to find that sweet spot.

Once I got it roughly working on the bench, I decided to make it a bit more permanent. I grabbed a small plastic project box. Managed to cram the Arduino, the relay module, and all the wiring inside. It was a bit of a rat's nest, but I secured things with some hot glue and more zip ties. Drilled a few holes for the wires (power in, sensor cable, pump wires out) and a hole for the USB cable just in case I needed to reprogram it without taking it all apart.

The "Field Test" and a Surprised Postman

With my slightly more robust contraption ready, I took it out to the garden. I propped it up on a brick, aimed it at a pathway the local felines seem to enjoy. Filled the water bottle, plugged it in, and waited.

It actually worked! Well, sort of. The first "intruder" it detected wasn't a cat. It was the postman, cutting across the edge of the lawn. He got a quick spray on his trousers. He was not amused, initially. I had to rush out and apologize, explain the whole crazy setup. Thankfully, he saw the funny side after a second and we had a laugh about it. Note to self: maybe put up a tiny warning sign next time, or at least don't aim it where the postman walks.

After that little incident, I did see it deter a couple of cats. They'd wander into its range, get a quick, harmless spritz, and then beat a hasty retreat. It wasn't a super-soaker by any means, more of a gentle "pssht, go away" kind of thing. But it did the job I originally intended, somewhat.

Looking Back and What's Next

It was a fun little build, definitely kept me occupied for a weekend. If I were to make a version two, I’d probably look for a slightly more powerful pump. And definitely a better mounting system, maybe something that could pivot. A 3D-printed enclosure would be cool too, make it look a bit more professional than a Tupperware box with wires sticking out.

I also thought about adding a bigger reservoir, or maybe even hooking it up to a garden hose for an unlimited supply, but that felt like it was escalating things a bit too much for a simple prank device. For now, it's a quirky little gadget that brings a smile to my face. And I learned that PIR sensors can be finicky little things. All part of the fun, right?