An LED-based water level indicator built with BC547 transistors, three color-coded LEDs, and conductive probes. Designed as a hands-on project for Digital Logic Design course to demonstrate transistor switching in real-world sensing applications.
Course: Digital Logic Design
Semester: 2nd Semester
Language/Technology: Analog Electronics, Transistor Switching
| Feature | Description |
|---|---|
| Three-Level Detection | Low (Red), Medium (Yellow), High (Green) |
| Transistor Switching | BC547 NPN transistors act as electronic switches |
| Visual Feedback | LEDs light up instantly when water touches probes |
| Current Protection | 330Ω resistors protect LEDs from overcurrent |
| Breadboard Prototype | No soldering required, easy to test and modify |
| Component | Quantity | Purpose |
|---|---|---|
| Breadboard | 1 | Circuit assembly |
| 9V Battery with Holder | 1 | Power supply |
| BC547 NPN Transistors | 3 | Electronic switches |
| LEDs (Red, Yellow, Green) | 3 | Level indicators |
| 330Ω Resistors | 3 | Current limiting |
| Jumper Wires | As needed | Connections |
| Conductive Probes | 3 | Water level sensors |
| Glass/Plastic Tank | 1 | Water container |
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Transistor as a Switch – Each BC547 transistor controls one LED. When water touches a probe, it provides a small base current that saturates the transistor, allowing a larger current to flow through the LED.
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Level Detection – Three probes are placed at different heights inside the tank:
- Low Level → Red LED turns on
- Medium Level → Yellow LED turns on
- High Level → Green LED turns on
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Current Limiting – 330Ω resistors limit LED current to ~21.8mA, preventing damage.
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Water Conductivity – Tap water contains minerals that conduct electricity, completing the base circuit when the probe is submerged.
| Water Level | Active LEDs | Color |
|---|---|---|
| No water / Dry | None | — |
| Low only | 1 | Red |
| Low + Medium | 2 | Red + Yellow |
| All three levels | 3 | Red + Yellow + Green |
All tests passed. Response time was instantaneous. No components were damaged.
| Circuit Diagram | Hardware Setup |
|---|---|
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