HardLabs

Water timer

atelierlelu·water-timer·hardware/water_timer_revB.kicad_pcb

Water timer PCB layout, top view — open source STM32 board by atelierlelu

About the Water timer PCB

Water timer is an open source STM32 PCB design by atelierlelu, published on GitHub under the CERN-OHL-P-2.0 license. It is a 4-layer board measuring 29 × 29 mm, with 21 components from 8 distinct parts.

Its main chip is the STM32L011F4PX, from the STM32 family. By type, the board carries 7 resistors, 6 capacitors, 5 diodes, 2 switches and 1 IC.

It belongs with the power & battery designs in this gallery.

From the project

A small battery-powered reminder to water a plant.

CC-BY-4.0. Copyright (c) 2026 Atelier Lelu.

A small device to remind you to water a plant. Battery powered but it lasts years. That's it.

Once assembled, enter setup mode to configure how often it waits before blinks (1, 3 or 7 days) by long pressing the top right button for 1.5 seconds. When you release you can cycle through durations by pressing the centre button - green LEDs will blink once (for 1 day), 3 times (for 3 days) or a long blink for 7 days. It auto saves after 10 seconds. Once the 1/3/7 days have passed, the device will blink green every minute (twice) to remind you to water…

Water timer, from the project README
From the project README

Main components on the Water timer

STM32L011F4PX

Water timer bill of materials (BOM)

21 components, 8 distinct parts — part numbers from the project's BOM.

QtyPartRefs
1
STM32L011F4PX
STM32L011F4Px
U1
2
SW_Push
SW1, SW2
2
C2297
Green
D1, D2
1
C84256
Red
D3
2
C7420332
D_Schottky
D4, D5
5
0.1U
0.1u
C1, C2, C4, C5, C6
1
10U
10u
C3
7
10K
10k
R1, R2, R3, R4, R5, R6, R7

Water timer design files

The KiCad project lives in the atelierlelu/water-timer repository on GitHub; these links point at the commit this page was built from.

Water timer: common questions

What microcontroller does the Water timer use?

The Water timer is built around the STM32L011F4PX, from the STM32 family.

How big is the Water timer PCB?

The Water timer measures 29 × 29 mm, has 4 copper layers and is 1.6062 mm thick.

How many components are on the Water timer?

21 components, from 8 distinct parts, with part numbers taken from the project's own BOM. The full bill of materials is listed on this page.

Where can I download the Water timer design files?

From the atelierlelu/water-timer repository on GitHub, which has the KiCad layout, the schematic and the BOM; the links under Design files point to each one.

Can I use the Water timer design in my own project?

Yes, under the terms of its CERN-OHL-P-2.0 license, which atelierlelu chose for the repository.

Can I test firmware for the Water timer without the hardware?

Yes. HardLabs builds a simulation of the board from its netlist and BOM, so you can run and debug STM32 firmware against it before you order a PCB.

Similar boards