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Hardware

Supported Sensors

Raspi-Sump works with the HC-SR04 ultrasonic distance sensor and compatible variants. For sump pit use, the JSN-SR04T v2.0 waterproof version is strongly recommended.

Sensor Notes
HC-SR04 Standard sensor, not waterproof
JSN-SR04T v2.0 Waterproof, recommended for sump pit use
JSN-SR04T v3.0 Not compatible — different protocol

!!! danger "JSN-SR04T v3.0 — Do not use" Version 3.0 uses a different communication protocol and is not compatible with Raspi-Sump. Verify the version before purchasing.

Voltage Divider Requirement

The HC-SR04 and JSN-SR04T sensors operate at 5V and return a 5V signal on the echo pin. The Raspberry Pi GPIO pins are 3.3V tolerant only — a 5V echo signal connected directly will damage your Pi.

A voltage divider on the echo pin is required to reduce the signal to 3.3V.

Simple Two-Resistor Divider

Sensor Echo ──┬── GPIO Echo Pin
              │
             R1 (1kΩ)
              │
             R2 (2kΩ)
              │
             GND
  • R1: 1kΩ between the sensor echo pin and the GPIO pin
  • R2: 2kΩ between the GPIO pin and ground

This divides the 5V echo signal to approximately 3.3V.

The trig pin (Pi → sensor) does not require a divider — 3.3V is sufficient to trigger the sensor.

GPIO Wiring

Any available GPIO pins can be used for trig and echo. The defaults are:

Signal Default GPIO Pi Header Pin
Trig 17 Pin 11
Echo 27 Pin 13
VCC (5V) — Pin 2 or 4
GND — Pin 6

!!! note "BCM numbering" Raspi-Sump uses BCM GPIO numbering, not the physical pin numbers printed on the Pi header. Set your chosen pins in raspisump.conf under [gpio_pins].

Sensor Placement

  • Mount the sensor at the top of the sump pit, facing downward
  • Set pit_depth in raspisump.conf to the distance from the sensor face to the bottom of the pit
  • Ensure the sensor has a clear line of sight to the water surface — avoid mounting near pipes or walls that could cause false reflections
  • The JSN-SR04T v2.0 has a minimum sensing distance of approximately 20cm — do not mount closer than this to the maximum expected water level

Raspi-Sump runs on any Raspberry Pi 2 or greater with Raspberry Pi OS Bookworm (v12) or Trixie (v13).