HardLabs

Wassermelder

HoFaLab·wassermelder·hardware/wassermelder.kicad_pcb

Wassermelder PCB layout, top view — open source RP2040/RP2350 board by HoFaLab

About the Wassermelder PCB

Wassermelder is an open source RP2040/RP2350 PCB design by HoFaLab, published on GitHub. It is a 2-layer board measuring 17.8 × 29.3 mm, with 13 components from 9 distinct parts.

Its main chip is the SC0918, from the RP2040/RP2350 family. By type, the board carries 5 resistors, 2 transistors, 2 connectors, 1 module and 1 capacitor.

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

From the project

HoFaLab Wassermelder (water alarm). Documentation and firmware for a small hardware project created at HoFaLab

To achieve a practically unlimited battery life, a small circuit is needed.

The voltage from the battery (J1) is disconnected from the Pico W via the P-FET transistor Q1. The resistor R1 pulls the gate of Q1 high and the transistor shut off. When the water sensor triggers, it pulls the gate of Q1 via R2 low, because the Resistance of R2 is a lot lower than R1. This pulls the gate voltage of Q1 below it's threshold voltage, allowing it to conduct and powering on the Pico W. The capacitor C1 stabilizes the voltage for the Pico W. The very first action of the Pico W is to pull it's pin GP0…

Wassermelder, from the project README
From the project README

Main components on the Wassermelder

SC0918

Wassermelder bill of materials (BOM)

13 components, 9 distinct parts — part numbers from the project's BOM.

QtyPartRefs
1
SC0918
Pico W
A1
1
AO3401A
Q1
1
AO3400A
Q2
1
BATTERY
J1
1
SENSOR
J2
2
Conn_01x01_Male
Mount1, Mount2
1
100µF/25V
C1
2
56kΩ
R1, R4
3
1kΩ
R2, R3, R5

Wassermelder design files

The KiCad project lives in the HoFaLab/wassermelder repository on GitHub; these links point at the commit this page was built from.

Wassermelder: common questions

What microcontroller does the Wassermelder use?

The Wassermelder is built around the SC0918, from the RP2040/RP2350 family.

How big is the Wassermelder PCB?

The Wassermelder measures 17.8 × 29.3 mm, has 2 copper layers and is 1.6 mm thick.

How many components are on the Wassermelder?

13 components, from 9 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 Wassermelder design files?

From the HoFaLab/wassermelder 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 Wassermelder design in my own project?

The repository has no license, so all rights stay with HoFaLab. Use it as a reference, and ask the author before reusing the design.

Can I test firmware for the Wassermelder without the hardware?

Yes. HardLabs builds a simulation of the board from its netlist and BOM, so you can run and debug RP2040/RP2350 firmware against it before you order a PCB.

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