A 12V supply is connected to the 12V positive wire, the current flows through a protection diode and a capacitor, in order to filter the voltage into a smoother flow. The zener resistor (R5) limits the current flowing to the zener diode, which regulates the voltage down to 9. 1 volts. Current for the various inputs of the Integrated Circuit is then
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further limited by the resistors R6, R7 and R8. Also 0V is connected to the negative lead which is connected to earth via R7 and the IC`s pin 11. After R5, pin 4 on the IC is connected to the 12V positive rail. The sensor input is connected to a supply of 0 to 1V which represents an actual oxygen sensor output range. A low voltage of 0. 01V will cause the red LED to light up, if a higher voltage of 0. 3V is detected by the oxygen sensor tester then the green LED will light up and when an even higher voltage of 0. 4 - 0. 5V is detected the yellow LED will light up, and finally when a high voltage of 0. 6 to 0. 9 is detected the red LED lights up. Testing Procedure: To test this circuit you will need to connect a 12V supply to the 12V positive wire and then the 0V negative wire to earth. At the same time a variable supply of 0 - 1V is to be connected to the supply wire, and again the earth to the 0V negative wire. The LED`s will emit light in relation to the variable voltage you have placed upon the circuit. Faults: I had to make two attempts at this circuit. My first attempt taken had many faults come along with it. All three of my diodes did not have drillings under them as they ran along the same track. My yellow LED had shorted after multiple times of taking out and putting back in the LED. Pin 10 and 13 were not connected as they should have been, also Pins 6 and 9 were not connected. I put a drill hole under the...
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