Blog 4 Oxygen Sensor Display Unit

This is our fresh new practical circuit diagram shown below:

A Oxygen Sensor Display Unit

Calculations:

To complete the circuit I need to know what resistor to use,here are all the calculations:

R2=R4: 

 Vs-Vd2-Vled/Iled

=12-0.7-11.8/0.0095

=9.5/0.0095

=1000= 1K ohms 

R3:

 Vs-Vd2-Vd4-Vled/Iled

=12-0.7-0.7-1.8/0.0095

=8.8/0.0095

=926≈ 1K ohms

R5:

 Vs-Vd2-Vd1/IeRm

=12-0.7-9.1/0.0056

=2.2/0.0056

=392≈ 390R

R8:

 Ir6

=9.1-0.63/R6

=8.47/10000

=0.85mA

 0.63-0.23/0.00085

=0.4/0.00085

=470R

R7:

=0.23/0.00085

=270R

So:

R2=R3=R4=1K R5=390R R6=10K(already known) R7=240R R8=470R

Here are all the components I need to make the circuit going:
3x 4001 diodes (Peak reverse voltage 50v,Pd 3w,average rectified forward current @75C 1A)
3x 5mm LEDs(Green,Red,Yellow)
1x Zener diode
2x 829 Capacitors
3x 1K resistors;1x 390R resistors;1x 10K resistor;1x 470R resistor;1x 270R resistor
1x LM324an OP-AMP(max supply voltage 32v,operating temp range 0C-70C) which the diagram is shown below:

How the circuit works:

The Green LED starts working when a voltage supply to the circuit just like 12V from the battery when the ignition is turned on in a car. When the car is running, if the engine is firing in a good fuel/power/air ratio, the oxygen sensor gets a good reading to tell ECU the feedback, the yellow LED is working at this time. If the car is running either too rich, too lean or other status, the signal changes and increases the voltage over 1V, red LED starts working so ECU knows engine is not running properly. 

This is  actually a potential divider circuit which means its divided into three regions.
The oxygen sensor will produce a voltage output from 0V-1V and supplies to the circuit, the three regions are Lean(Green LED) from 0-0.23V, Normal(Yellow LED) from 0.23-0.63V and Rich(Red LED) from 0.63-0.99V
For the two input terminal of each OP-AMP, all of the inverting input side receives the voltage signal from the power supply which has already been divided into those three regions to match the OP-AMP of each LED, once the the non-inverting input side receive a voltage from the signal input, one of the LED will lights up when the voltage meets its voltage region.

How do I test if the circuit is working?

First connect 12v to red wire which is the power supply to the circuit and negative to black wire which is the ground of the circuit, then connect signal to the green wire which is the sensor input.

1. Make the signal input to 0V or a little bit more say 0.08V, the green LED should lights up, this voltage indicates the oxygen sensor detected engine is running lean
2. Adjust the signal slowing to around 0.23V and onwards the green LED should go off and yellow LED lights up, this voltage indicates the oxygen sensor detected the engine is running normal
3. At last keep turing up the signal input to above 0.63V and keep it within 1V, the yellow LED should go off and red LED lights up, this voltage indicates the oxygen sensor detected engine is running rich.

This picture shown below is what I have designed the circuit on Lochmaster

After I wired all the components on the board to test the circuit, it did not work straight away.

I found out 3 problems after I started trouble shooting:

·      I did not ground terminal 11

·      I did not ground the Zener diode and Capacitor 2

·      I put all the LEDs both legs on the same line which had the current flowing through legs not LED.

The first 2 problems were because I did not check the circuit probably and when I went through the circuit again I realized they are not connected.

I should also had the LEDs legs on different line so current can go through LED from positive to negative for the last problem.




This video shown below is when I was testing the actual Oxygen Sensor Display Unit I made :

What should I improve and what did I learn?

If I am going to build one of these circuit again in the future, first thing I should improve is to remember more about how every component works, second thing I should improve is to remember rechecking the circuit more careful, because this time the circuit did not work at the first time because 2 parts were not grounded,but next time it could be something else even worse and would probably destroy components or circuit.

Blog 3 Injector circuit board

What we are doing here is to build a Injector Circuit Board which the diagram is shown below

Calculations:

Assume the current flow through both LED is 20mA from range 10mA-50mA

  R14=R15

=Vs-Vled/Iled

=12-2/0.02

=500≈470R

Because we want the transistor to be in saturation mode,so we need the current going through Base close enough it's minimum value.Assume current Ib=2mA

  R13=R16

=Vsingal-Vbe/Ib

=5-0.7/0.002

=4.3/0.002

=2150≈2k2

So R14=R15=470R and R13=R16=2k2

Components list:


2x 470R resistors
2x 2k2 resistors
1x 5mm yellow LED and 1x 5mm red LED
2x BC547 transistors which the datasheet is shown below:

This is how I designed the circuit from lochmaster

How the circuit works and why is it called Injector circuit?

This circuit is basically using transistors to switch device on and off.

There is one separate signal input for each transistor and LED, when a 5v supplies to one of them,the transistor switches on it's controlled LED and it should flashes fast or slow by adjusting the frequency of the signal current.

When use this circuit in a car injection system, LEDs are actually injectors. Each injector has one transistor for switching them on and off, a battery voltage will be supplied through the injectors to all the Collector terminals of the transistors by connecting them in parallel and a voltage signal from ECU will be connected to Base terminal, the ECU will turn on the circuit and energize the injector by grounding the Emitter terminal to each transistor by the pre-programmed order.

This is why it is called an Injector Circuit.

This is the actual circuit I made

How to test the circuit?

To test if the circuit is working or not, connect 12v to the red wire which is the power supply to the circuit and ground the black wire.Then connect 5v signal to yellow wire which is the Base terminal to LED1 which is the yellow LED and it should lights up, process the same thing to LED2 which is the red LED. Also the LEDs should flash when vary the 5v signal frequency.

Results:

I made the circuit going in two tries

On the first try,the green LED was working but not the red one which eventually I found out that I have done the LED and resistor in wrong location which was the resistor sit behind the LED,that way the current will flow through From LED to resistor which current is supposed to be flowed through from resistor to LED

On the second try after I switched the position of the resistor and red LED,the whole board works well as it should be.

Reflection:

This circuit is fun and easy to start with, I was planing to make it work on the first attempt but I didn't, the reason I did not make it work was because I did not design it well and the circuit was a mass so it is not easy to tell which component is in the front or which one is at the back.

If I have the chance to make this again, I will improve the way how I design it on the lochmaster and make it looks nice too, a more clearer circuit will be hard to make a trouble and easy for fault finding as well.

References:

auto101.com

wikipedia

Unitec Moodle

Vijay Naidu