Car Voltage Gauge

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The Car Voltage Gauge is
based on 3 parts. The input circuit is an Analog to Digital Converter
(IC2 CA3162E). The purpose of this chip is to sample an analog voltage
and convert it to a decimal value which is read by a Display/Decoder
Driver (IC1 CA3161E). This chip will turn each seven segment display on
through the driver transistor Q1 – Q3. The power is derived from the car
and is converted to 5 volts by the 5 volt regulator. The circuit works
as follows: The 10uf capacitor is charged up by the cars voltage. Its
value is then read by IC2 and a decimal value of that voltage is
provided to IC1 which multiplexes the three display units.

Each display is turned on sequentially with its appropriate value
displayed. The transistors Q1 through Q3 control the drive to each seven
segment display. By monitoring the cars voltage with an accurate
multimeter you can adjust the “Zero Adj.” pot and the “Gain Adj.” pot
for accurate readings. LED 1 and 2 are
optional. They can be used to indicate power on or can light up a cut
out display that says “Volts”. This can be made by a plastic module that
has a thin plastic cover on it with the word “Volts” cut into it. The LED’s would be mounted inside the module.