Specifications

CIRCUIT IDEAS
erates approximately 1Hz waveform. The
output of IC1 serves as the clock input
for the counter built around IC2 and IC3.
The circuit can be reset by momen-
tarily depressing switch S1. When the cir-
cuit is powered on, capacitor C1 will be
initially uncharged, with the result that
all the flip-flops are cleared. Now, as the
capacitor starts charging toward the posi-
tive rail, the clear inputs of all the flip-
flops go to logic 1 (and stay there) and
the flip-flops are enabled. The counter be-
gins to count in a particular se-
quence, as shown in Table I. When-
ever the output of a flip-flop goes
high, the associated transistor con-
nected at its output saturates. It
drives current through the array of
LEDs connected as collector load,
thereby causing them to turn ‘on’.
Upon arrival of first clock pulse,
the LSB will be set. The counter will
now count 0001. This means that
the array of LEDs at the centre of
the display panel will be lit. When the
next clock pulse arrives, logic 1 will also
be copied to its preceding flip-flop and the
counter will read 0011. As a result, the
array of LEDs adjacent to the centre ar-
ray (on both sides) will be lit. In this fash-
ion, the count progresses upwards till it
reaches 1111, when all the arrays of LEDs
will be lit. Now the wings of the peacock
are fully spread. At this stage, you may
manually swing the display board both
ways, holding it at its centre bottom by
TABLE I
Johnson Counter Count Sequence
D C B A Decimal LED’s LIT
MSB LSB Count Upon Count
0 0 0 0 0 Nil
0 0 0 1 1 L1 to L3
0 0 1 1 3 L1 to L7
0 1 1 1 7 L1 to L11
1 1 1 1 15 L1 to L15
1 1 1 0 14 L4 to L15
1 1 0 0 12 L8 to L15
1 0 0 0 8 L12 to L15
0 0 0 0 0 Nil
your thumb and forefinger to resemble a
dancing peacock.
The countdown sequence of the
counter will be initiated upon the arrival
of the next clock pulse, which causes the
count to read 1110. At this stage, the ar-
ray of LEDs at the centre of the display
panel will be turned ‘off’. The counter then
counts down to 1100 upon the arrival of
the next clock when the array of LEDs
adjacent to the centre array (on both
sides) will also be turned ‘off’. In this man-
ner, the counter continues to count down
till the contents read 0000, when the
whole array of LEDs are turned ‘off’ and
one full cycle is completed. The counter
then starts the counting sequence all over
again.
The circuit can be assembled on a gen-
eral-purpose PCB. The LEDs can be
stacked into an array as per the pattern
shown in the figure. The circuit requires
both +5V and +12V DC supplies. The cir-
cuit can be used as a festival display.
S.C. DWIVEDI
an overload shutdown facility, while those
incorporating this feature come with a
price tag.
The circuit presented here is an over-
load detector which shuts down the in-
A
n overload condition in an inverter
may permanently damage the
power transistor array or burn off
the transformer. Some of the domestic in-
verters sold in the market do not feature
verter in an overload condition. It has the
following desirable features:
• It shuts down the inverter and also
provides audio-visual indication of the
overload condition.
• After shutdown, it automatically re-
starts the inverter with a delay of 6 sec-
onds. Thus, it saves the user from the
inconvenience caused due to manually re-
setting the system or running around in
darkness to reset the system at night.
• It permanently shuts down the in-
verter and continues to give audio warn-
ing, in case there are more than three
SIDDHARTH SINGH
INVERTER OVERLOAD PROTECTOR
WITH DELAYED AUTO RESET
Fig. 1
116