Specifications
CIRCUIT
IDEAS
‘low’ or
vice
versa).
The out-
puts of
flip-flops
drive the
corre-
sponding
relays, in
conjunc-
tion with the four relay driver transistors
SL100. The wires earlier removed are con-
nected to this circuit. On the switch panel
board, the micro-switches are connected,
and under the board the connections are
wired as suggested above.
Relays RL1 though RL4 are 9V, SPST-
type micro-relays of proper contact rat-
ings.
The circuit may be expanded for six
switches by using one more IC 7476, and
an IC ULN 2004 which has an array of
seven Darlingtons for driving the relays.
So two more micro-switches and relays
may be connected in a similar fashion.
This circuit can be assembled on a
general-purpose PCB and the total cost
should not exceed Rs 300. It is suggested
that the circuit, after assembly on a PCB,
may be housed in a box of proper size,
which may be fitted on the wall in place
of a normal switchboard.
TABLE I
Displayed Counter IC4’s active Relay
count count low output activated
0 000 Q0 NIL
1 001 Q1 RL1
2 010 Q2 RL2
3 011 Q3 RL3
4 100 Q4 RL4
5 101 Q5 RL5
0 000 Q0 NIL
T
he circuit presented here is that
of a digital fan regulator,
variable to provide five speed lev-
els as catered for in ordinary fan regula-
tors. The circuit makes use of easily avail-
able components. An optional 7-segment
display with its associated circuitry has
been provided to display your choice of
fan speed.
The heart of the circuit is a modulo-6
binary counter, built around IC2 and IC3
(IC 7476) which are dual JK flip-flops.
The counter counts up in a straight bi-
nary progression from 000 to 101 (i.e. from
when the clock goes from high to low. Let
us begin with the assumption that the
counter reads 000 at power on. The
monoshot built around IC1 (NE 555) pro-
vides necessary pulses to trigger the
DIGITAL FAN REGULATOR
0 to 5) upon each successive clock edge
and is reset to 000 upon next clock. The
count sequence of the counter has been
summarised in Table I.
Each flip-flop is configured to toggle
C.K. SUNITH
RUPANJANA
171