The museum alarm circuit uses the logic diagram in Fig. 1. A display case opens a reed switch, giving input A a value of 1. At night, input B is set to 1 by...
Question 1 Report
The museum alarm circuit uses the logic diagram in Fig. 1. A display case opens a reed switch, giving input A a value of 1. At night, input B is set to 1 by the security computer. The siren is connected to the output.
(a) State the output when A is 0 and B is 0. [1]
(b) Give all binary input pairs that make the siren output 1. [3]
For each input, the road tunnel controller uses the circuit in Fig. 1. V is 1 when poor visibility is detected. W is 1 when the road surface is wet. The variable-speed sign should show a reduced limit only when exactly one of these conditions is true.
(a) State the name of the gate. [1]
(b) Give the sign output for V = 1, W = 0 and for V = 0, W = 1. [2]
(c) State the sign output for V = 1, W = 1. [1]
(d) Give one reason why an OR gate would not meet this requirement. [1]
Answer Details
The museum circuit is an OR gate, so the siren operates whenever at least one input is 1. The road-tunnel circuit is an XOR gate, which outputs 1 only when the inputs are different.
- Museum alarm (a) When \(A=0\) and \(B=0\), neither OR input is active, so the output is 0. [1]
- Museum alarm (b) The input pairs that produce siren output 1 are A = 0, B = 1 [1], A = 1, B = 0 [1], and A = 1, B = 1 [1].
- Road tunnel (a) The gate is XOR, also called exclusive OR. [1]
- Road tunnel (b) For \(V=1, W=0\), the sign output is 1 [1]. For \(V=0, W=1\), it is also 1 [1]. Exactly one condition is true in both cases.
- Road tunnel (c) For \(V=1, W=1\), the XOR output is 0. [1]
- Road tunnel (d) An OR gate would not meet the requirement because it would give output 1 when both inputs are 1. The requirement says the output should be active only when exactly one condition is true. [1]
Download The App On Google Playstore
Everything you need to excel in your exams
