Oxygen Sensor Complete

Oxygen Sensor Write Up Parts Used

LED 35000 MCD Emitted Colour: Red Vf (V) Max: 2.6 If mA: 75 Vf (V) Type: 2.2

LED 35000MCD Emitted Colour: Yellow Vf (VMax:2.6 If mA: 75 (Vf) Type:2.2

LED 35000MCD Emitted Colour: Green Vf (V) Max: 2.6 If mA: 75 (Vf) Type 2.2

Electrolyte Capcitors x2

9V1 Zener Diode

LM324AN 14pin Intergrated Circuit

R1 390R +/- 5% 0.5 Watts

R2 470R +/- 5% 0.5 Watts

R3 10K +/- 5% 0.5 Watts

R4 270R +/- 5% 0.5 Watts

R5/R6/R7 1K +/- 5% 0.5 Watts

D1/D2 1N4001 50V Silicone Diode 1 Amp

Jumper Wires

Additional 1V power supply

How it Works

Connected with a 12V supply, current flows through the first diode. The voltage is then lowered to 11.3V due to the operating voltage of the diode. Current then flows through the capacitor and towards the first LED, dropping the voltage by a further 1.8V, (9.5V)which then goes towards a 1K Resistor, and then to the 7th pin of the IC. With the Yellow LED, current flows through another 1N4001 Diode, which drops the voltage by 0.7V (10.6V), and then through the LED itself dropping the voltage by 1.8V (8.8V), through another 1K resistor and then to the 8th pin of the IC. For the last LED, there are no additional diodes, so voltage drop only occours across the LED itself (9.5V), which goes through a 1K resistor and then to the 14th pin. When the board is connected to a 12v supply on the positive and negative rails, only the Red LED should turn on. There is a lead on the 12th pin, (called the sensor input) we may now alter which LED's will come on, depending on the varying 1V voltage. As voltage is increased to 0.3V, the red LED will turn off and the yellow LED will turn on. When voltage is increased to 0.7 V, the yellow LED then turns off, and then the green LED will turn on.

Fault Finding

My first board I constructed had faults due to bad soldering. My LED's would blow and components would not operate, so I completely redesigned my board to make it much more user friendly and less complex. When my second board was constructed, My LED's would not turn on when additional voltage was added. After hours and hours of trying to solve the problem, I realised my IC was wired up wrong, and had to change my design once more. With only 1 day left to complete this circuit, I constructed one more, only to find out that my new board shorted out when I connected it to a power supply. With no other alternatives I had to scrap my board and start my write-up.