Fire alarm circuit design
Design a fire alarm circuit: There is a fire alarm system with three types of fire detectors: smoke, temperature and ultraviolet
light.
In order to prevent false alarms, the alarm system only generates alarm control signals when two or more types of detectors send out fire detection signals. Design a circuit that generates an alarm control signal and verify it on a breadboard. (The preview of the circuit in this question requires the preparation of two design plans, using any two of the three components 74138, 74153 and 74151. You can add the necessary gate circuits, complete the whole design process and take photos and upload them before the experiment.)
(1) Record the experimental data of the fire alarm circuit, where A, B, and C are smoke, temperature and ultraviolet light detectors respectively. When a fire is detected, it is 1, otherwise it is 0. Y is the alarm output signal. When an alarm is required, it is 1, otherwise it is 0. After completing the experiment on the experimental board, record the experimental results as follows:
Write the minimum term
Y=m3+m5+m6+m7
Design circuit
2.1 Using 74138
74LS38 decoder has 3 binary code input terminals A2, A1, A0; 8 decoding output terminals Y0~Y7 active low level, 3 enable terminals G1, G2AN, G2BN, among which G1 is set is high level, G2AN and G2BN are set to low level so that the decoder can work normally.
Simulation waveform diagram
2.2 Use 74153 to design a circuit.
How to use the 74153 data selector to output the minimum terms
1C0–D0, 1C1–D1, 1C2–D2, 1C3–D3, 2C0–D4,
2C1–D5, 2C2–D6, 2C3–D7
F=m0D0+m1D1 +m2D2+m3D3+m4D4+m5D5+m6D6+m7D7
And because the minimum term expression of output Y is Y=m3+m5+m6+m7,
so D0=D1=D2=D4=0; D3=D5=D6=D7= 1.
The circuit diagram is as follows
Simulation waveform diagram
