Self-powered shower timer - inspired by teenagers spending ages in the shower; along with an excuse to build something.
Saw something similar in a random catalog years ago.
Features:
- Uses water flow generator to create the power needed
- Compact-ish design to screw into the shower feed
- RP2040 as the micro-controller
Search for Water Turbine, and lots of different things turn up on Amazon and eBay.
Decided to take a chance on this one
- Voltage was 12v - had no idea what type of current/voltages would actually come out. Knowing wthat something in 5-3.3v would be needed seemed that opting for 12v would give some room to drop this and get some current.
- The connectors were 1/2" threaded which is the UK standard for showers.
On testing it seemed that with only a modest water flow it could get to 12v; taking it apart later determined that there was a regulator and capacitor inside that help to regulate the voltage. Current to power a couple of LEds was quite sufficient.
This was witih a decent mains-level water pressure.
There's a 5mm tri=colour LED, driven with 3* 2n2222 transistors from the GPIO pins.
For power I had one these very small boards available SparkFun BabyBuck Regulator Breakout - 5V
The controller I had available was a Seed XIAO RP2040
To address the 'elephant-in-the-room' - a dual core processor is way too much; an embedded arduino, or a PIC controller would have been far better. Even smaller and even less power.
But for 2 reasons; one the only controller that was small enough was the XIAO; plus after I'd managed to unsolder some of the pads previously it wasn't really up for anything needing SPI or I2C.
Second reason is you can use Rust!
Note that the brass converter which is internally threaded to 1/2". so this was needed to connect to the shower outlet - with washer as well.
The white outer casing a small plastic container from aquarium fish food; cleaned, label removed and cutdown. Glued with circuit inside.
Contained in this repo based on this tutorial
When the power is connected; the software works through using 3 GPIO pins to control the LED. It'll move through Green-Blue-Red-Flashing Red. Moving ever 4 minutes, and ending on the flashing red.
To build the software please see the tutorial mentioned above, the two main commands I used where
cargo build --release
elf2uf2-rs target/thumbv6m-none-eabi/debug/xiao_rp2040_rs op2.uf2
Rather than cargo run which would to try and download the code to the XIAO, I was running this on WSL2 so the transfer was a manual step.
Bascially Yes; does it reduce the shower time - well maybe it won't long term when the novelty wears off.
The big issue is if you turn on the water slowly; the XIAO doesn't start properly. This will be connected to the power; and could be fixed by a hardware reset at some point.
And really it would be so much better to use a different microprocessor (PIC probably) and also use a proper PCB.