Battery Indicator

The IN914 (little glassy diode) and the zener diodes all have bands on the body which must be put in the direction shown on the drawing. The bands ar ` e at the K end of the diodes. A magnifying glass will help to locate the bands and also to check the values of the zeners. To identify them, the following procedure will help : with a magnifying
Battery Indicator - schematic

glass find the diode that` has the code IN4148 printed on the glassy surface. This is the silicon diode usually referred to as IN914, NOT a zener. The zeners may have their voltage printed on the side, or they may have numbers. Remember that there are two 6V8 zeners and one 11V, so 4. The molex pins are to connect the wires to the circuit. Push them through in their holes and solder. Bare the Red and Black hook-up wires, tin them and solder to the pins. Red is Positive, Black Negative 5. Connect the circuit to a power supply with a variable Voltage control, but make sure the polarity is co ect. Wind up the voltage and check the performance of your circuit against the quoted performance figures. This circuit depends for its operation upon the different voltage drops across different colour LEDs. At 20mA the voltage drops across red, yellow and green LEDs are typically 1. 7, 3. 0 and 2. 3 volts respectively. When the vehicle battery voltage is too low to cause either ZDI/ZD2 or ZD3 to conduct, Q1 and 02 are held off by R3 and R5. Under these conditions the yellow LED is forward biased and conducts `via D1 producing a potential of about 3. 7 volts at the "A legs" of the LED`s. When the supply rises above about 11. 6 volts ZD3 conducts, biasing Q2 on. By virtue of its lower voltage recuirements the green LED conducts, reducing the voltage at the "A legs" of the LED`s to approximately 2. 6 volts. This is not enough to bias...

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