Specifications

CIRCUIT IDEAS
T
his circuit uses only one octal D-
type latch, IC 74LS373, and some
associated circuitry to control
eight different gadgets. To control more
devices, identical circuits, in multiples,
can be used. The circuit incorporates
the following features:
(a) Individual ‘on/off’ control for all
channels.
(b) Emergency ‘off’ control for all
channels.
(c) Immediate ‘on’ control for all
channels.
(d) LED indication for ‘on’ channels.
(e) Optional push-to-on buttons or
tactile switches.
When one presses the ‘on’ switch
(S1) of channel 1, a logic low is applied
to data input pin D0. The same level
appears on the data output pin Q0,
because latch-enable pin LE (active
high) is connected to Vcc, and the out-
put-enable OE (active low) is pulled
down using resistor R9. At the same
time, Q0 output is fed back to D0
input, which thus keeps the common
S.C. DWIVEDI
P. SABARINATHAN
MULTICHANNEL CONTROL
USING SOFT SWITCHES
junction of D0 and Q0 (marked ‘A’ in
the figures) at low level, even after
releasing on switch S1. This low level
is applied to the base of transistor
T1 through diode D9 to turn it on,
and RL1 is activated. LED1 also
glows to indicate that channel 1 is
on. The other channels can also be
switched on, as desired, in a similar
manner.
To switch off channel 1, off switch
S9 of channel 1 is pressed to apply
logic high to point A. Because
199