Specifications

CIRCUIT IDEAS
in 1-volt steps. Dial II has ten resistors of
1,100-ohm value each. This dial is marked
from 0 to 0.9 volt in 0.1 volt steps. Dial
III has eleven resistors, having a value of
1,210-ohm each, with dial marking from
0 to 0.09 volt in 0.01 volt steps. The val-
ues of the resistors in a given ring are 1.1
times the values of the resistors in the
preceding ring. The bridge shown in the
illustration would read the value of un-
known voltage as 6.43 volt (when the null
detector reads ‘0’) as detailed below:
Dial I - 6 volts
Dial II - 0.4 volt
Dial II - 0.03 volt
Total : 6.43 volt
Note: 1. For the above example, the
equivalent circuit has been reduced to a
simpler form by EFY— in three stages,
as shown in Fig. 2, for the benefit of the
readers.
more
closely the
bridge
output can
be read. If
lower
value re-
sistors are
used, the
bridge
output impedance becomes lower. How-
ever, this would increase the power dissi-
pation in the bridge.
The principal limitation of this ar-
rangement is the allowable power dissi-
pation of the resistor in the first ring,
across which the full supply voltage is
applied. Resistors in dial I must be able
to withstand the full supply voltage of 10
volts. Regulated power supply (10-volt)
only should be used in this circuit.
2. Please do not confuse the dial volt-
ages mentioned inside each of the three
dials with the actual voltages across the
associated resistors, which would be dif-
ferent.
The tighter the tolerance of the resis-
tors, the more accurate will be the mea-
surement of the unknown voltage. For
null detection, any micro-ammeter or gal-
vanometer can be used. However, the
more sensitive the null detector is, the
S.C. DWIVEDI
A
ll of you must have observed a
dancing peacock, spreading out
its beautiful feathers, turning
around, closing them, and then doing it
all over again. The author has attempted
to reproduce a similar effect using a set
of LEDs arranged according to a prede-
termined pattern.
The circuit is built around two dual
JK flip-flop ICs 7476, which have been
wired as a Johnson counter. The count
sequence of this counter is shown in
Table I. The free running oscillator built
around IC1, a popular timer NE555, gen-
ELECTRONIC DANCING PEACOCK
C.K. SUNITH
115