Water Level Sensor Circuit Design
Thought for 1 min 58 sec
Based on Flux knowledge-base guidance and safe GPIO practices, here’s my recommendation:
-
Pull-down resistor
- Use a 100 kΩ pull-down on the Pico GPIO to define a solid LOW when no water bridge is present.
- At 5 V this draws only 50 µA, minimizing corrosion and power drain.
-
Voltage level shifting (only if you must keep the probe at 5 V)
- Because the Pico’s GPIO is not 5 V-tolerant, add a simple divider:
- R1 = 6.8 kΩ from the probe to the GPIO node
- R2 = 10 kΩ from the GPIO node to ground
- This yields ≈2.98 V at the pin—well above the ~2 V logic-high threshold and within 3.3 V tolerance.
- Because the Pico’s GPIO is not 5 V-tolerant, add a simple divider:
-
Better alternative
- Power the probes from the Pico’s 3.3 V rail instead of 5 V and omit the divider. The 100 kΩ pull-down alone is then sufficient.
- Or implement a capacitive water sensor using PCB pads (per soil-moisture-sensor best practices) to avoid galvanic corrosion altogether.
Part suggestions (all < 60 % power rating, AEC-Q200, good stock):
Table
| Function | Part |
|---|---|
| 100 kΩ Pull-down | CRCW0603100KFKEA |
| 6.8 kΩ Divider R1 | CRCW08056K98FKEA |
| 10 kΩ Divider R2 | RC0805FR-1310KL |
Let me know which option you’d like to implement or if you’d prefer the 3.3 V-powered variant—then I can help place and wire them in Flux.
Use 3.3V rail
Implement 5 V divider
Ask wiring divider
Capacitive sensor option
