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The water level indicator is one of the most popular beginner PCB projects — it teaches sensing, transistor switching, and multi-LED output all in one simple board.
Components You'll Need
NPN Transistors (BC547) x3-5, one per level LEDs (any color) x3-5, one per level Resistors (1K for base, 220Ω for LED) 9V Battery + connector Probe wires (bare copper strips, one per level + one common)
How the Circuit Works
Water conducts electricity (not perfectly, but well enough for this). Each sensing probe is placed at a different height inside the container. When water rises high enough to touch a probe, it completes a weak current path to the transistor's base, switching that transistor on and lighting its corresponding LED.
- A common probe sits at the very bottom of the container, always submerged once there's any water at all
- Additional probes sit at increasing heights — low, medium, full
- Water bridging the gap between the common probe and a level probe turns that level's transistor on
- Each transistor independently drives its own LED — so multiple LEDs can be lit at once as water rises past several levels
Designing the PCB in PCB Wizard
1. Group Each Level as a Repeating Block
Since each level uses the identical transistor+resistor+LED pattern, design one level's layout first, then duplicate it for the other levels. This keeps your layout consistent and is much faster than placing each one from scratch.
2. Place Transistors With Airflow in Mind
Leave a small gap between adjacent transistors rather than packing them edge to edge — it makes probing with a multimeter during testing much easier, and matters more here since you'll likely be adjusting this board during setup.
3. Route the Common Ground Line as One Continuous Track
All transistor emitters (or collectors, depending on your exact wiring) typically share a common ground path. Route this as a single wide track running along one edge of the board, rather than separate tracks to each transistor — cleaner, and easier to trace visually when debugging.
Tip: Label each level pad directly on the PCB silkscreen (L1, L2, L3...) if PCB Wizard's text tool supports it — it makes connecting the right probe wire to the right pad much less error-prone during assembly.
4. Bring Probe Connections to the Board Edge
Route each probe's input track to a connector or exposed pad along one edge of the board, where it's easy to attach the wires that will run to the actual probes inside the water container.
Watch out: Never connect this circuit directly to mains-derived power without a properly isolated, low-voltage supply (like a 9V battery) — water and any mains-connected circuit is a genuine safety hazard.
Testing Your Board
Before placing probes in an actual container, test each level manually — briefly touch a wire between the common probe pad and each level pad in turn, and confirm the correct LED lights each time. Only move to the real water test once every level checks out individually.
