Oxygen sensor display unit
Today's blog will focus on an oxygen sensor simulator. By simulator I mean it isn't actually an oxygen sensor but a small circuit hooked up to a main power supply and a much smaller variable power supply so we can adjust the voltage going through certain parts of the op amp.Basically it will display three different coloured LEDS which will turn on individually when a certain voltage runs through them. This Blog will consist of the calculations needed to get it operational and the components chosen for the task. I will also show the circuit in working order and maybe try and reflect on ways to improve it.
Calculations
.Well first things first we needed to get some calculations prior to starting the assignment so we could figure out what components we needed.
The picture above (made it as big as I can) called "Brons calculations"shows the circuit in its most basic and understandable form. As you can see the calculations for each resistor has been shown in a mathematical equation. The minimum amount of amps required to activate an led is 9.5ma. I decided to use 10ma just to be on the safe side and to also make my calculations a little bit easier. Basically to work out the size of the first resistor (R2) we had to use the VIR triangle.
R2= V/I R2=12v-0.6v(diode d2)-1.8v(led 1)=9.6v
10ma(0.01a)= 960Ω
With this equation we were able to work out the equation for resistor 2 to 4. Resistor 5 was slightly different as we had to take the zener diode into the equation as well which was 9.1v and the IzRm already displayed the appropriate amps which was 5.6ma. The equation for resistor 5 was
R5= 12v-0.6v(diode)-9.1v(D1 Zener diode)=2.3
R5= 2.3v/5.6ma(0.0056a)= 410.71Ω 2dp
R6 was already given to us as a 10k (10,000Ω) resistor. We still needed to use the available values to get the amp value for this part of the circuit (which should be the same form R6 to R8). This way we can figure out the values for R7 and R8.
amps for R6= 9.1v-0.63v=8.47v
8.47v/10000Ω= 0.000847amps
Now that we had the available current we could determine the values for the last 2 resistors.
R7= 0.23v/0.000847amps= 271.55Ω 2dp R8=0.4v/0.000847amps= 472.26Ω
These calculations concluded which resistors we should use.
Components
Ounce we had figured out what size resistors we needed it was just a matter of getting the components on the circuit diagram listed above. Getting resistors and other components with values exactly the same as our calculations is very difficult. Because of this we used ones that were available with similar values (getting the exactly right sized resistor is either very rear or very expensive). As long as they didn't vary to much it would still function properly. Our list of components and the ones actually used are listed below.
R2=960Ω - 10000Ω R3=900Ω-1000Ω R4=960Ω-1000Ω R5=410.71Ω-390Ω
R6=10kΩ R7=271.55Ω-270Ω R8=472.26Ω-470Ω
3* 1n4001 diodes- 1n4007 diode
3* LEDS (red,yellow and green).
2* IIC104 capacitors.
one 9.1v Zener diode
one op amp
one bread board
After acquiring all these components we then simply had to put it all together on a breadboard. HAHA allot easier said then done. Although it probably would of been rather simple to simply connect wires to each individual component, the bread board had the problem of being very small and compact. Also because all the lines in the bread board join everything up when components are run in the same horizontal line we had to offset everything and place the off amp right in the center. This in turn lead to an incredibly large amount of small individual wires that had to be cut and stripped to make the circuit work. After doing this tedious task the only real goal but that stage was to MAKE IT XXXXEN WORK. This was the finished product.
As you can see it was a freaking maze of wires. Not only this it took me almost an hour to figure out what was wrong with it as the yellow LED wouldn't turn of when the green one turned on. Turns out the diode was being run horizontally (meant the negative and positive were touching) and needed to be offset . I recorded 2 videos. The first one was pretty good and described what an actual oxygen sensor does and how this simulates it. Sadly they cant be more then 30 seconds long otherwise they get to big and cant be sent via email (WTF?). Because of this i had to do another much shorter one which was incredibly xxxxen vague. Because of this I will give a better explanation of what an oxygen sensor does in writing and how this is shown with my simulator circuit.
Oxygen sensor, what does it do?
ECUs data base. This info helps the ECU decide how to adjust the fuel ratio. So it can be described something like this in the simulation.....
low voltage 0.1v-0.4v (green LED lights up) the car is running lean, need to add more fuel to the air fuel ratio.
Middle voltage 0.41v-0.7v (yellow LED lights up) car is running efficiently, car will try to keep running to this ratio
High voltage 0.71v-1v
One thing to consider though is that although an oxygen sensor does all this it still needs to take other variables into account like whether the engine is still cold or whether its struggling to get up a hill (which in turn will need allot more fuel). Because of these variables the ECU will sometimes adjust the fuel ratio to an unfavourable value to cope with these demands.
Conclusion and things I would do to improve it?
To conclude this blog I would like to state i was just incredibly glad that it actually worked (spent so much time wiring it up). I cant really imagine i would like to spend any real time trying to improve it as you get premade boards with all the components displayed on it to show were they go. All you have to do is solder the components in. Because of this I cant justify finding ways to improve this circuit on a bread board as its neither time nor cost effective (and incredibly xxxxen stressful). In saying that this the exercise has proven to be rather challenging in terms of problem solving and patience so it seems like it was a worth while experience as i still learned quite a bit. Sadly I was unable to to the whole exercise as I'm currently in Australia at my brothers wedding. So I hope you take this into consideration when you read this blog and see how much effort I put into the writing content.
References=http://highfields-arc.co.uk/beginner/foundation/3a-btechbasic.htm
PS When you put the websites in the caption the pictures don't show up, real annoying.
As you can see it was a freaking maze of wires. Not only this it took me almost an hour to figure out what was wrong with it as the yellow LED wouldn't turn of when the green one turned on. Turns out the diode was being run horizontally (meant the negative and positive were touching) and needed to be offset . I recorded 2 videos. The first one was pretty good and described what an actual oxygen sensor does and how this simulates it. Sadly they cant be more then 30 seconds long otherwise they get to big and cant be sent via email (WTF?). Because of this i had to do another much shorter one which was incredibly xxxxen vague. Because of this I will give a better explanation of what an oxygen sensor does in writing and how this is shown with my simulator circuit.
Oxygen sensor, what does it do?
ECUs data base. This info helps the ECU decide how to adjust the fuel ratio. So it can be described something like this in the simulation.....
low voltage 0.1v-0.4v (green LED lights up) the car is running lean, need to add more fuel to the air fuel ratio.
Middle voltage 0.41v-0.7v (yellow LED lights up) car is running efficiently, car will try to keep running to this ratio
High voltage 0.71v-1v
One thing to consider though is that although an oxygen sensor does all this it still needs to take other variables into account like whether the engine is still cold or whether its struggling to get up a hill (which in turn will need allot more fuel). Because of these variables the ECU will sometimes adjust the fuel ratio to an unfavourable value to cope with these demands.
Conclusion and things I would do to improve it?
To conclude this blog I would like to state i was just incredibly glad that it actually worked (spent so much time wiring it up). I cant really imagine i would like to spend any real time trying to improve it as you get premade boards with all the components displayed on it to show were they go. All you have to do is solder the components in. Because of this I cant justify finding ways to improve this circuit on a bread board as its neither time nor cost effective (and incredibly xxxxen stressful). In saying that this the exercise has proven to be rather challenging in terms of problem solving and patience so it seems like it was a worth while experience as i still learned quite a bit. Sadly I was unable to to the whole exercise as I'm currently in Australia at my brothers wedding. So I hope you take this into consideration when you read this blog and see how much effort I put into the writing content.
References=http://highfields-arc.co.uk/beginner/foundation/3a-btechbasic.htm
PS When you put the websites in the caption the pictures don't show up, real annoying.
Very good, you just need to re-check your lean/rich answer to what voltage you get from the Oxygen sensor signal. It should be the other way around. Also add something for fault finding and diagnostics.
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