| This circuit can control any one out of 16
devices with the help of two push-to-on switches. An up/down counter acts as a
master-controller for the system. A visual indication in the form of LEDs is also
available. IC1 (74LS193) is a presettable up/down counter. IC2 and IC3 (74LS154) (1 of 16
decoder/demultiplexer) perform different functions, i.e. IC2 is used to indicate the
channel number while IC3 switches on the selected channel. Before using the circuit, press
switch S1 to reset the circuit. Now the circuit is ready to receive the input clock. By
pressing switch S2 once, the counter counts up by one count. Thus, each pressing of switch
S2 enables the counter to count up by one count. Likewise, by pressing switch S3 the
counter counts downwards. The counter provides BCD output. This BCD output is used as
address input for IC2 and IC3 to switch one (desired channel) out of sixteen channels by
turning on the appropriate triac and the corresponding LED to indicate the selected
channel. The outputs of IC3 are passed through inverter gates (IC4 through IC6) because
IC3 provides negative going pulses while for driving the triacs we need positive-going
pulses. The high output of inverter gates turn on the npn transistors to drive the triacs.
Diodes connected in series with triac gates serve to provide unidirectional current for
the gate-drive. |
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