Specifications

CIRCUIT IDEAS
ing through the channels continues un-
til it receives an audio signal exceeding
the preset threshold value. The skip
switch S1 is used to skip a channel even
if audio is present in the selected chan-
nel. The number of channels can be eas-
ily extended up to ten, by using addi-
tional 4066 ICs.
WATER TEMPERATURE
CONTROLLER
VIJAY D. SATHE
RUPANJANA
T
he circuit presented here controls
the temperature of water as well
as indicates it on an LED
bargraph. When the temperature of wa-
ter is 0o C, none of the bargraph dis-
play LEDs glows. But as the tempera-
ture starts increasing above approxi-
mately 30o C, LEDs from LED1 through
LED8 of the bargraph start glowing one
after the other. When temperature is
around 30oC, only LED1 would be ‘on’.
For temperature greater than 97dig C,
all display LEDs will be ‘on’.
To detect the temperature of water,
commonly used resistance-temperature
detector (RTD) PT100 is used. It is con-
nected to one of the arms of a Wheat-
stone bridge as shown in the figure RTD
PT100 has a resistance of 100 ohms
98