The circuit described here is a Priority Lamp Circuit which gives priority in switching. Switches SW1 to SW4 are push-to-off type or push button type, as desired. Normally, pushing of any switch will turn ‘on’ the corresponding relay, i.e. pushing of SW1 enables the npn transistor T1 and hence relay RL1 operates. The logic section of Priority Lamp Circuit is designed to get a controlled high output. The pressing of one switch disables the operation of all switches and results in priority in switching. In normal cases, all switches are closed and all relays are in ‘off’ state. When two switches are pressed in one step, it checks priority and one relay turns ‘on’ in Priority Lamp Circuit.
The circuit of Priority Lamp Circuit comprises five ICs. IC1, IC2 and IC4 (7408) are quad 2-input AND gates. IC3 (7432) is a quad 2-input OR gate. IC5 (7404) is a hex inverter which can replaced by IC 7400 with some specification modifications. The feedback loop between output and input lines of IC4 and IC5 gives controlled high output for one relay.
Select SPDT relay for dual mode operation for priority in ‘on’ and ‘off’ for the connected lamps as shown in the circuit diagram of Priority Lamp Circuit.
The input and output lines of the digital section of Priority Lamp Circuit can be connected to the other digital circuit to detect the input line from which the first high occurs. It is also used to make non-interrupted multichannel system. When any one channel is in working state the other channels are automatically disabled in Priority Lamp Circuit.
NOTE: – In the switch SW5 (a–d) position 1 is for priority-ON, 2 is for priority-OFF
PARTS LIST OF PRIORITY LAMP CIRCUIT
Resistor (all ¼-watt, ± 5% Carbon)
R1 – R4 = 2.2 KΩ
IC1, IC2, IC4 = 7408
IC3 = 7404
IC5 = 7432
T1 – T4 = SL100
SW1 – SW4 = Push – To – Off Switchs
SW5 (a–d) = 4 Poles 2Ways Switch
RL1 – RL4 = 5V, 100Ω SPDT relay
Lamp1 – Lamp4