Reading a Float Switch Sensor on a Raspberry Pi 4B (Water-Level Alarm)

Step by step

1. Drag Raspberry Pi 4B and a Breadboard onto the Canvas.
2. Drag the Float Switch Sensor onto the Canvas — like the Servo or HC-SR04, it connects only through drawn wires, not a breadboard.
3. Hover over its 2 pins to confirm the labels: Signal and GND.
4. Drag a Resistor onto the breadboard and select it — in its settings panel, set Resistance to 10 and the unit to kΩ.
5. Wire GND → a Pi GND pin.
6. Wire Signal → a Pi GPIO pin you'll configure as an input (e.g. physical pin 37), and also Signal → one leg of the 10kΩ Resistor. Wire the Resistor's other leg → a Pi 3.3V pin — this is the external pull-up the switch needs; without it, Signal has no defined level at all when the switch is open.
7. Go to the Code tab and write a script that polls the pin:

import RPi.GPIO as GPIO
import asyncio
 
GPIO.setmode(GPIO.BOARD)
SIGNAL = 37   # adjust to match your wiring
 
GPIO.setup(SIGNAL, GPIO.IN)
 
while not should_stop():
    level = GPIO.input(SIGNAL)
    print("Float UP — contact closed, tank full" if level == 0 else "Float DOWN — contact open, tank not full")
    await asyncio.sleep(0.5)

8. Click Start. The Console should print "Float DOWN — contact open, tank not full" repeatedly — this is the switch's default state (open, matching a real normally-open float switch at rest with no liquid lifting it).
9. While the script is still running, click directly on the Float Switch Sensor's own body on the Canvas (not one of its 2 pins). Its floating ball shifts position and its status text flips to CLOSED — and on the very next poll, the Console switches to printing "Float UP — contact closed, tank full". Click it again to flip back.
10. This click-to-toggle works at any time — before Start, or live while the simulation is running — exactly like the Tact Switch's own press. Unlike a real mechanical float, nothing here "resets" on its own: it stays in whichever state you last set it until you click it again.

What “working correctly” looks like

• At rest (never clicked), the switch reads OPEN and GPIO.input() returns 1 — the pull-up resistor holds the pin HIGH with nothing shorting it.
• Clicking the switch's body flips its own visual (the floating ball's position and its OPEN/CLOSED status text) immediately, and the very next GPIO.input() read reflects it — CLOSED reads 0 (the switch's own 0Ω contact overrides the 10kΩ pull-up), OPEN reads 1.
• Toggling works identically whether the simulation is stopped or running — no need to click Stop first to change the float's simulated position.
• The state persists across multiple reads without being clicked again — this is a toggle, not a momentary press like the Tact Switch's own button.

If something’s wrong

• GPIO.input() always reads 1 (HIGH), even after clicking the switch → make sure you clicked directly on the switch's own body, not one of its 2 pin markers — the pins are small targets near the bottom edge and easy to miss on a first click.
• GPIO.input() always reads 0 (LOW), even when the switch's own status text says OPEN → double-check the Resistor's other leg actually reaches a real Pi 3.3V pin (not left dangling, and not accidentally wired to GND) — a pull-up with no real 3.3V source behind it can't hold the line HIGH.
• Nothing changes when clicked at all → confirm GND is genuinely wired back to the same Pi ground the pull-up's own reference uses — an isolated GND leaves the whole net with no defined state regardless of the switch's own position.
• Wanted a continuous water-level reading instead of just full/not-full → this component is deliberately digital-only, matching a real mechanical float switch's own fixed trip point — for a continuous analog reading, a different sensor (with its own real analog output) would be needed; this simulator doesn't model one for float switches specifically.