02 Sensor Display Circuit

O2 Sensor Display Board

Component List

• 1 Green LED 1.8v
• 1 Red LED 1.8v
• 1 Yellow LED 1.8v
• 1 LM324N IC: Max Pd = 1310mW,  Max operating Temp: -25 ~ +85°C
• 4 IN4001 Diodes
• 1 9V1 Zener diode
• 4 470Ω Resistors
• 1 10KΩ Resistor
• 1 390Ω Resistor
• 1 270Ω Resistor
• 2 0.1uF Capacitors
• Jumper Wires

Calculations

Technical Explanation

This circuit is designed to show an Oxygen sensors voltage reading, which it obtains from the air fuel mixture after combustion.

It does this by lighting up a red, green or yellow LED to show the conditions of the air fuel mixture.

It uses a IC Chip (integrated Circuit) Called the LM324 Comparator. This comparator compares voltage from the oxygen sensor to a pre-set voltage caused by the resistors on the board.

Basically the series resistors have two voltages which it uses to compare with the O2 sensors voltage. This is between 0.23V and 0.63V.

The list below explains what the different coloured LEDs represent when they are lit:

• Less than 0.23V: Green. Air fuel ratio is lean
• Between 0.23V and 0.63V: Yellow. Air fuel ratio is said to be stoich (14.7:1) which is optimum mixture
• Above 0.63V: Red. Mixture is said to be rich 

Reflection

I had a bit of trouble getting the circuit working because of not wiring the chip up correctly and a faulty Yellow LED. But once these problems were diagnosed and repaired it began working correctly. 

If I was to build this circuit again I would probably make the layout more simpler so that wiring it up is a lot easier and fault diagnosing is easily performed. 

By doing this circuit I learned how to wire up vera boards correctly and also how to find out problems with it. I also learned to be very careful with how I soldier the circuit and to check everything over each time a new part is added and soldiered to the board.

Bread Board Design

Loch Master Design

Vera Board Design

Vera Board Soldiering

Injector Circuit Assignment

Injector Circuit Assignment

Component List

Component	Peak Voltage	Max Current Flow	Reverse Voltage	Total Power Disipation	Operating Temp
INJ2: LED Red	2.2V	10mA	5V	180mW	-55 to +100
INJ1: LED Yellow	1.8V	20mA	5V	60mW	-55 to +100
Q1, Q2, Q3: Transistor BC547 x3	45V	Collector: 100mA Base: 200mA	N/A	500mW	-65 to +150

Other Components

• RC1, RC2: 340Ω Resistor
• RB1, RB2: 1000Ω Resistor
• R3, R4: 470Ω Resistor

Calculations Done

These are the calculations I performed to find out the components I needed to make circuit work correctly:

Injector Circuit on Breadboard working with no wires connected

Injectors working simultaneously

Injectors working Sequentially

Reflection

I had a lot of trouble getting my circuit to work. The main problem I had was with getting all the components to work how they are meant to the biggest thing that was incorrect was having my LEDs on the same line with both legs in-line. I corrected this by re-soldiering the LEDs with each leg on its own path. I also had minor problems with getting the current to flow in the correct places I fixed this by breaking the copper paths on the vera board.  After my second attempt to complete the circuit I got it working correctly. 

Lochmaster Circuit

Completed Vera board Circuit

Transistors

Background

A BC547 NPN
 type transistor

Transistors amplify current they can be used with a IC (or chip) a LED, relay or other high current device with a resistor to convert the charging current to a charging voltage then the transistor is used to amplify this voltage.

It can also be used as a switch, which is either fully ON with maximum current, or fully OFF with no current. The amount of current amplification is called gain.

There are two types of transistors a NPN (Negative, Positive, Negative) or a PNP ( Positive, Negative, Positive) They are made from a semi-conductor material and the letters refer to the different layers of the transistor. Most now days are NPN types as they are the easiest type to make from silicone. Each terminal is labelled either B (base) C (collector) or E (emitter).




Technical Explanation


As I said above transistors are made of three different layers of silicone which can either be one of two types a NPN or a PNP. Each of these three layers have a terminal attached, they are the base, collector, and emitter. 
Referring to a NPN type transistor, the base will have a positive charge and the other two terminals will have a negative charge (collector and emitter).
When no current is flowing In the transistor the P-type silicone layer is short of electrons and the two N-type layers have extra electrons. The P-type layer has holes in it, where the electrons should be. This normally prevents current flow and acts like a barrier.
This prevents electron flow from emitter to collector and this means that the transistor is in a OFF state.
When the transistor is connected to a power supply and a positive charge is put through the base the electrons begin to move from emitter to collector. The emitter becomes negatively charged because of the positive voltage to the base, and the collector becomes positively charged and this causes electrons to be pulled from the emitter to the base and then to the collector. This cause the transistor to be switched to its ON state.

Diagram showing how current flows from base,
 to allow flow from emitter to collector

The small voltage to the base creates a much larger current flow from the emitter to the collector and it becomes a amplifier and a switch at the same time. Because if no current is flowing to the base there will be no flow from emitter to collector. 
Also regulating the voltage to the base allows the current flow to be controlled accordingly to what is required of the circuit. 


Testing Transistors


Testing is done using a multimeter on diode test mode and putting the probes across each terminal. If the transistor is working correctly each pair of terminals should get a certain reading:

• From Base to Emitter it should behave like a diode and only conduct one way.
• From Base to Collector it should also conduct one way
• From Collector to Emitter there should be no conduction either way.

If you don't no what each terminal is you can also find this out using the multimeter as well. From emitter to base there should be a higher voltage drop than from collector to base. For example With the meter touching each terminal you should get the following readings at each pair:

Example of terminals of a Transistor 

this can be different depending on 

transistor type and manufacturer

• Meter touching 1 and 2 (+-) OL
• Meter touching 1 and 2 (-+) OL
• Meter touching 1 and 3 (+-) 0.665V
• Meter touching 1 and 3 (-+) OL
• Meter touching 2 and 3 (+-) 0.621V
• Meter touching 2 and 3 (-+) OL

Problems if faulty


A transistor normally does not fail if it is used in a circuit it is designed for and it is not exposed to excessive heat from a soldering iron for example. But if it is used incorrectly and fails this would be because it has exceeded its usage range. If it fails the circuit would be broken and no current will flow and would need replacing to repair it.  

Electronic Components

Resistors

Background Information

Resistors restrict the flow of electrical current. They do this to prevent damage to electrical components in a circuit. for example L.E.D (light Emitting Diode) require a 1KΩ resistor to prevent it from burning out too quickly and allowing it to last.

They come in a range of values which refer to how much resistance the resistor will create. These values are measured in Ohms (Ω). These resistances will vary from around 1KΩ to a maximum of 1MΩ. 1kΩ is equal to 1000Ω and 1MΩ is equal to 1000000Ω.

The resistance of a resistor is obtained by reading a colour code that is on the resistor this is represented by coloured bands on the component itself. 

this is a 2kΩ Resistor

 The colours represent numbers ranging from 0 - 9 each numeral has its own colour and the position of the colour has a different meaning. The first 2 bands going from left to right are the first 2 numerals of the number and the third band is the multiplier or number of zeros. Referring to picture on left the red is 2 and the black means 0 and the second red is 2 which means two zeros so its value is 2000Ω or 2kΩ. 

The forth band is its tolerance or how much resistance it will have at cold or hot operations. This resistor has a gold band which  means it will have + or - 5% resistance change depending on the resistors temperature.

 Resistor Colour Chart

  Technical Explaination

Resistors are made from two terminals on either side of a carbon rod.

The rod is a form of semiconductor which does not conduct electricity well, and causes resistance, this resistance is created by heat. This causes the current flow to be regulated by it being lost through heat dissipation thus decreasing the current flow in the circuit, which can be used to reduce damage to components, that are not rated to run on the full amount of current flow caused by the voltage source, for example in a12V circuit.

Test Procedure

Testing a Resistor. Resistor tested was a 10KΩ
 the closest rating of the resistor was 9.92KΩ as shown on meter

Testing of resistors is simple all that is required is a multimeter with a resistance setting. Using the probes of the meter on ether side of the resistor a reading can be obtained which is displayed on the meter.     


Problems if Faulty


Resistors are not known to fail often but if they do it is because there has been an excessive voltage surge or wrong value resistor used for application, that causes it to fail. This will cause a break in the circuit stopping current flow.


Reflection


What I learned from working with resistors was how to read the value of a resistor and how the tolerance value effects it, and also how to work out how temperature can effect the resistance it causes. eg.


Brown, Black, Brown, Gold = 100Ω with 5% tolerance (+ or -)
which means with very high or very low temperatures the resistors value or resistance can go up or down


so: 
100Ω-5%= 95Ω when the resistor is at a low temperature.


100Ω+5%= 105Ω when the resistor is at a high temperature.


This can become a large difference depending if the resistor is a high resistance value.