3. Automatic Night Lighting Control
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A street lighting system must activate when the light sensor signal is low. Since standard NOT gates are not available, the circuit is implemented using a NAND gate configured as an inverter.
To understand how this line is evaluated, we examine the truth table for a NAND gate where inputs A and B are tied together (A = B):
| Input (A and B tied) | NAND Output |
|---|---|
| 0 | 1 |
| 1 | 0 |
Calculation breakdown:
- When the Sensor is 0 (Dark): Both inputs to the NAND gate are 0. The output of a NAND gate is 1 when any input is 0; therefore, the Street Light Output is 1.
- When the Sensor is 1 (Day): Both inputs to the NAND gate are 1. Since both inputs are high, the NAND gate outputs 0, turning the light off.
Circuit Implementation:
- Inversion Gate: Connect the Ambient Light Sensor to both inputs of a NAND gate.
- Connect: Map the output of the NAND gate to the Street Light Output probe, ensuring the street light activates automatically when it is dark.