OXYGEN SENSOR CIRCUIT

In this we used the following components:-

12v Battery

3 LED's:

1x Red led

1x Yellow led

1x Green led

1x Op Amp  LM324

3 diodes 1N4001

7 resistors (R2=1KΩ, R3=1KΩ, R4=1KΩ, R5=380Ω, R6=10KΩ, R7=270Ω, R8=470Ω)

1 zener diode 9v1

2 capacitors  0.1uF

A O2 sensor is located in your exhaust (just after the exhaust manifold), and as the name states it is senses the amount of oxygen in your exhaust gases.

CALCULATION

R2, R3 & R4

I= 9.5mA =0.0095A

The voltage drop in R2 is at 9.6v, Vd=12 - 0.6 - 1.8 =9.6v

R=V/I =9.6/0.0095 =1010.5Ω

The voltage drop in R3 is at 9v, Vd=12 - 0.6 - 0.6 - 1.8 =9v

R=V/I =9.6/0.0095 =947Ω

The voltage drop in R4 is at 9.6v, Vd=12 - 0.6 - 1.8 =9.6v

R=V/I =9.6/0.0095 =1010.5Ω

R5=

Power supply voltage is at 12v, Vd of crossing diode D2=0.6v, Vd of zener diode D1=9.1v

Vd of R5 = 12-0.6-9.1= 2.3v

I=5.6mA=0.0056A

R=V/I =2.3/0.0056 =411Ω

R7 an R8

R6=10KΩ Voltage drop in crossing R6 is at 8.47v

The volage are at 9.1v and 0.63v before the R6 and after the R6 each.

So, Vd=9.1-0.63 = 8.47v

ohms law I=V/R =8.47/10,000 =0.000847A

R8=

VD= 0.4

Vd= 0.63 - 0.23 =0.4v

R=V/I =0.4/0.000847 =472Ω

R7 consumes the voltage which voltage drop is at 0.23

Vd= 0.23 - 0 =0.23Ω

R=V/I =0.23/0.000847 =271.5Ω

Total resistance RT=R6+R8+R7 =10,743Ω

I=9.1/10,743 =0.000847A

OXYGEN SENSOR

n the early 1980s when oxygen sensor was first introduced, it has only one signal wire. This sensitive wire was designed so that it only takes low voltage signal under 1 volt. This crude design has a major flaw; it takes too much time for the sensor to give signal to the engine computer.

It is the computer’s job to regulate the fuel mixture after the sensor warms up which sometimes takes about 10-15 minutes. This time delay can gets worse when the weather gets cold and would dump a lot of raw fuel to the catalytic converter (CAT). This leads to premature CAT failure and high fuel .But since 1994 to 2006 the oxygen sensor has been upgraded to solve this problem.

The O2 sensor is mounted in the exhaust manifold to monitor how much unburned oxygen is in the exhaust as the exhaust exits the engine. Monitoring oxygen levels in the exhaust is a way of gauging the fuel mixture. It tells the computer if the fuel mixture is burning rich (less oxygen) or lean (more oxygen).

In this first of all I made the circuit on breadboard and then took a pcb board and then made the whole thing on it. It was not too easy. I Faced few problems.

REFLECTION

One thing I learnt from this task was to never overlook any aspect of the wiring diagram. As this can cause in the circuit to not work and can also cause damage to the components of that circuit. Always look carefully for the current flow and follow it as you are making your circuit. I also improved on my soldering. I learnt that you are meant to heat up the component leg as well and not just the area around it. Although you have to be care full not to overheat the leg otherwise you can damage the component you are trying to solder. If i was to do this task again a second time the one thing i would make a change on would be the fault finding exercise. I would want a more challenging fault to diagnose.