Boolean Logic (AQA GCSE Computer Science)

A logic circuit is being developed for an audio advert in a shop that plays automatically if a customer is detected nearby.

• The system has two sensors, A1 and A2, that detect if a customer is near. The audio plays if either of these sensors is activated.

• The system should only play if another audio system, S, is not playing.

• The output from the circuit, for whether the advert should play or not, is Q.

Complete the logic circuit for this system.

Write a Boolean expression to show how the output D is calculated from the inputs A, B and C in Figure 3.

You must use the correct symbols for the Boolean operators in your expression.

A game uses three sensors.

A red light (R) in the game switches on if all of the following conditions are true:

• sensor D is off

• sensor L is on

• sensor W is on

Another circuit in the game will output True if any two sensors are activated or if all three sensors are activated. This has been represented as the Boolean expression:

(W . D) + (D . L) . (W . L)

The expression contains an error.

Identify one choice that shows the expression with the error corrected.

A green light (G) in the game switches on if all of the following conditions are true:

• sensor D is off

• sensor L is off

• sensor W is on.

Write a Boolean expression for this logic circuit.

You must use Boolean expression operators in your answer.

Draw a logic circuit for the following scenario.

A sewing machine is running (R) if either the foot pedal is on (F) or the hand dial is on (H) but not both.

You should use only the gates AND, OR and NOT in your answer.

A farmer uses an automated system to indicate if soil conditions are right for planting.

The conditions are right for planting if the soil is:

• warm

• wet

• the correct acidity.

Figure 2 shows the logic circuit for this system

Figure 2

The inputs to the system are:

Soil temperature (T):
0 if the soil is cold
1 if the soil is warm.

Soil moisture (M):
0 if the soil is dry
1 if the soil is wet.

Soil acidity (A):
0 if the soil is the correct acidity
1 if the soil acidity needs adjusting.

The output (P) is:
0 if the conditions for planting have not been met
1 if the conditions for planting have been met.

Complete the truth table for the circuit in Figure 2.

The farmer wants to modify the system so that it will indicate that the soil conditions are right for planting if at least one of the three conditions has been met.

Describe changes that could be made to the logic circuit in Figure 2 to allow this to happen.