Components :
12v Battery
3 LED's:
1x Red led
1x Yellow led
1x Green led
1x Op Amp LM324
3x Rectifier diode 1N4001
1x Zener Diode 9v1
2x Capacitors
7xResistors
R2=1KΩ, R3=1KΩ, R4=1KΩ, R5=380Ω, R6=10KΩ, R7=270Ω, R8=470Ω ( i had to round up my calculations to find the right resistors we had)
Wires
Calculations:
It was really simple , we used ohms law to find out the resistance . First we find out the voltage and divide it by the led (amps) resistance = Voltage / Amps
LED= 1.8v 9.5mA/0.0095A (we converted into amps )
R2
Voltage drop = Power-Diode-LED
Vd= 12v-0.6-1.8= 9.6v
Then we use ohms law to find out the resistance
R=V/I - 9.6/0.0095= 1010.5Ω
R3
Voltage Drop = Power-diode D2-diode D4-LED
VD=12v-0.6-0.6-1.8=9v
and again we use ohms law to find out the resistance .
R=V/I 9v/0.0095=947Ω
R4
This will be the same as R2
Voltage Drop = Power-diode-Led
VD=12v-0.6-1.8=9.6v
By using ohms law we get the resistance by R=V/I
9.6/0.0095=1010.5Ω
We have 12volts power then we have a diode which is 0.6 now we have 11.4volts.
12v-0.6=11.4v
Now we can calculate R5
VD= 11.4-9.1=2.3vd . We got 9.1 from the zener diode (9V1)
9.1-0.63=8.47vd we got 0.63 from point 1
Now we use ohms law to calculate the resistance R=V/I
2.3v/0.0056a= 411Ω
R6 = 10k
We use ohms law to find out the amperage I=V/R
8.47v/10,000= 0.000847a
R8
We minus the two points 0.63 - 0.23 which gives use 0.40v now we can calculate the resistance using ohms law R=V/I
0.40v/0.000847a = 472 Ω
R7
Using ohms law we find the resistance
R=V/I 0.23v/0.000847= 271.5Ω
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| Op Amp |
The circuit is divided into 3 parts , depending on the sensor output it will show one led on.
The Green LED shows that the mixture is LEAN.
The Yellow LED shows that the mixture is Normal.
The Red LED shows the the mixture is RICH.
When we wire it up onto a vechile while idling it will show the green led turn on because it is running lean and as we start to cruise the LED will change to yellow and the green led will turn off to show us that the car is running normal as we start to accelerate the red led will turn on to show the vechile is running rich
Problems:
I had a slight problem when i went to test my circuit. There was contact with one of the wires which caused both the green and yellow led to turn on. So we did a fault test on each conponent using a multimetre to see the different voltages at each point and compare with my calcutaions. Then we did another visual check and saw a connection which caused the problem. Now we found and fixed the problem and circuit is working normal
Reflection:
If i had the opportunity to do this circuit again i would add more LED's to show a more accurate reading . By building this circuit i now know how an op amp functions and how the Oxygen sensor works
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| Circuit on the bread board |
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| The red pin is power , the yellow pin is ground and the blue pin is the sensor input. |
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| Wired up and tested on bread board and it works :) |
Here is a Video of my O2 Sensor circuit on bread board , the green Led shows it is lean , then the yellow Led shows its normal and the red to show it is running rich
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| This is the board we are going to solder on , it is very easy for us because it shows us where to place the components |
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| Added all the components , and looks nice and tidy |
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| Perfect soldering , and leds. |
This video shows my circuit working , and as we can see green led turns on for lean mixture then yellow for normal and then red for rich. And goes back to yellow as we decrease speed then stops at green
For next week i will put the cirucit nicely into a box and test it on the engines down at RM-1066
This week was our last week , i have cut out a box for fit my circuit and see the LED's . Also we had to create a fault on our pcb boards in pairs and diagnose the problem.
Me and my partner had to make a fault on our pcb boards , i had made a cut in R2 and my partner had made a cut in R4.
My prediction was that if R2 was cut the RED led would not work but the rest of the circuit will and that if R4 was cut that the Green led will not work.
Next i did a Voltage drop to make sure every component is getting the voltage they are suppose to be getting.
I predicted right the cut in R4 made the Green led not work the the red & yellow leds worked fine and the cut in R2 made the red led not work but Green & yellow worked as normal.
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| As you can see there is a cut made on R4 |
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| Black box , need to drill the holes and place the leds inside . |
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| All finished and boxed nicely |
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| Diagnosing the problem for fault finding |
A video showing my circuit wired up to an engine which went into closed loop.
When we connect the O2 sensor to a car and start driving as we accelerate the RED LED will turn as the mixture gets RICH and if we start to slow down to cruise the Yellow LED turns on to show the mixture is NORMAL as we come to stop the GREEN LED lights up to show the mixture gets LEAN.
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