17. Automatic Night Lighting Control

Solution Explanation

From the behavioral table, Street Light Output = 1 when Ambient Light Sensor = 0, and becomes 0 when the sensor is 1.

So the required function is NOT.

NOT gate is prohibited, so use the available NANDgate.

Let:

A = Ambient Light Sensor
Y = Street Light Output

The required function is:

Y = A'

Using the Boolean law:

A · A = A

Therefore:

Y = (A · A)'

Now check the NAND operation when both inputs are connected to A:

This produces the required NOT behavior.

Therefore:

Street Light Output = (Ambient Light Sensor · Ambient Light Sensor)'

Connect Ambient Light Sensor to both inputs of the NAND gate to generate Street Light Output.