Post Three: Electronic components

Capacitor  

A capacitor is an electronic component that stores electrical charge. It does this by providing ground when there is an open circuit (switch is open). This storage of electrical charge prevents voltage spikes from happening. A capacitor consists of two metal plates very close together. They are separated by an insulator. When connected to a battery or a power source electrons flow into the negative plate and charge up the capacitor. This charge still remains when the battery or the power source is removed. The amount of charge a capacitor can store depends on the capacitance of the capacitor (measured in Farads F). Capacitors are also used in circuits to smooth-en out the current flow. This allows for the circuit to have a constant smooth flow of current. 

In practical we looked at the relationship between the amount of current flowing through a circuit and the amount of time it took for the capacitor to charge. This was done on the breadboard. We had a 12V power supply and we used a bridging wire as the switch. The amount of current flow was controlled by the resistors (resistance in the circuit). The capacitor used was measured at 100uF. We did three tests, each with a different value of resistor (different amount of current flow). Here's a table showing our recordings.

Circuit Number	Capacitance (uF)	Resistance (Ohms)	Observed Time (ms)
1	100 (uF)	1000 Ohms	500 ms
2	100 (uF)	100   Ohms	45   ms
3	100 (uF)	470   Ohms	250 ms

As we can see the relationship between the current flow and the charge times is very simple. The more current flow in a circuit the quicker the charge time of the capacitor. This is because more current means greater electron flow, hence the capacitor fills up quicker. 

Relays   

A relay is an electronic component that uses a low amperage circuit to switch on a higher amperage circuit. This low amperage circuit is called a control circuit. The control circuit will have a coil of wire that creates a magnetic field around it when the circuit is powered and earthed. The switching circuit (higher amperage circuit) will have a set point of contacts that are switched on and off by having the magnetic field pull (attract) the points over to connect with another set of points. 

The control circuit of the relay usually gets its power from the battery. It will also have a switch that will turn on and off the circuit. This switch can either be on the positive side of the circuit or the negative side of the circuit. The circuit can be switched by either a switch, a sensor with a switch inside it, or an ECU (electronic control unit) that does the switching based on a logic circuit.

The switching circuit (high amp circuit) also gets its power from the battery and this circuit is connected to the component.

Transistor (Bipolar)
A transistor is an electronic component that uses a small amount of current to open the gate for a high current and voltage flow. A bipolar transistor is constructed of three semiconductor plates and are either a PNP transistor or a NPN transistor. As we know protons and electrons attract each other. The semiconductor plates in a transistor either consist of extra protons (+) or extra electrons (-). The PNP transistor has two plates with extra protons and only one plate with extra electrons. The NPN transistor does the opposite of that. Now as we know current consists on electrons. Say you put the P plate in a circuit. The extra protons will attract the electrons flowing in the circuit. This attraction will cause electrons to flow through this plate. The transistor uses this principle. The transistor has three legs the Base, the Collector and the Emitter. (The base is the gate). The base is connected both to the emitter and the collector but neither of those two (the emitter and the collector) are connected with each other. The base is like the control circuit in a relay. When current flows through the base of the transistor it then connects the collector to the emitter allowing for high voltage and high current flow. We call this opening the gate.

Here is a picture of the transistor symbol and the semiconductor construction

How to Check the legs of a transistor
Not all the transistors out there come with their legs named. So we need a way to determine them without mixing them up. Now as we know that the base leg is connected to both the emitter and the collector. This means that we will only have voltage readings when we connect the base terminal to either the emitter or the collector terminal. These voltage readings show us how much voltage is required to push the current through those points. Hence showing us that we have a circuit. Now we know that there are two types of base terminals in a transistor. P-type and N-type. This is determined by which lead of the multimeter is touching the base terminal. 
Here are the multimeter check readings for testing both a PNP transistor and a NPN transistor


* E and C reverse: 1(+) and 2(-): "OL"
* E and C reverse: 1(-) and 2(+): "OL"
* E and B forward: 1(+) and 3(-): 0.655 V
* E and B forward: 1(-) and 3(+): "OL"
* C and B forward: 2(+) and 3(-): 0.621 V
* C and B forward: 2(-) and 3(+): "OL"

This shows us that leg number three in this transistor is the base leg. Now as we can see in both the combination of the conductive readings we got our negative (-) lead on the base terminal hence indicating that it is a PNP transistor. Collector to base junction will always have a lower voltage reading to the emitter to base junction. Therefore with these set of reading we can determine that leg two is the collector leg and that leg one is the emitter leg. For the NPN transistor we would get voltage readings when the positive lead of the multimeter is on the base leg.


Voltage Dividers
A voltage divider is a simple linear circuit that produces an output voltage that is much lower than its input voltage. The voltage divider divides the voltage among the components of the divider. A simple construction of this will be three resisters wired up in series as shown below. 

Now as we know from series circuits the available voltage after each resistor will be lower. Same principle applies over here. Lets say that V in is 12V and you was V1 to be 7V, V2 to be 2V and V3 will naturally be zero or very close to it. Now to create these outputs you need to add resistance to the circuit. Lets say that you decide to set R1 at 800Ohms. To find the current flowing through the circuit you will have to use ohms law (I = V/R). V in this case is 5V (12V minus 7V = 5V). 5V is the voltage drop across resistor one. So V = 5V and R = 800Ohms. (5V/800Ohms = 0.00625A) now we know the current running through the circuit. This makes it easier to set resistor two and three. To set resistor two you will use ohms law again (R=V/I). In this case I is 0.00625A and V is 5V (7V minus 2V). So 5V divided by 0.00625A equals 800Ohms. Therefore resistor two is set at 800Ohms. We repeat this step to find out the value of resistor three. 2V divided by 0.00625A equals 320Ohms. Therefore resistor three is going to be set at 320Ohms.
This is how a voltage divider works. V1 can be used to power up low beam head lights and V2 can be used to power up park lights in a vehicle.


MOSFET   
A MOSFET is another type of transistor and it is used for amplifying or switching electronic signals.  MOSFET stands for Metal Oxide Semiconductor Field Effect Transistor. This transister differs quite a lot from the bipolar transistor (mentioned above). A MOSFET is voltage operated and not current. It is capable of handling much higher voltages and amperage compared to a bipolar transistor. It uses the same principle tho. It has three legs just like a bipolar transistor and they work similar to the ones of the bipolar transistor. The three legs are Gate, Drain and Source. Gate acts like the base leg. It turns on and off the flow between the drain and the source. But unlike a bipolar transistor the Gate is voltage operated. It does not need current flow to turn on. It requires voltage. The metal oxide gate electrode is electrically insulated from the main semiconductor by a thin layer of insulating material usually glass. This insulated metal gate can act like a capacitor and therefore it can be damages easily by static electricity. Since the gate is isolated there is no  current flow through he gate.

Here's a link of a youtube video that explains more about MOSFETs and how it works.
"http://www.youtube.com/watch?v=j47Yk7bJbxw&feature=related"












   
 

Post Two: Fuel Injector Circuit

The task at hand this week was to design and wire up a circuit which mimics a fuel injector circuit. Two LED's and transistors were used for this circuit. Voltage was supplied to the base of the transistor, this then turned on the connection between the collector and the emitter of the transistor. This action grounded the LED circuit and allowed the LED to turn on. The LED turning on indicates that the fuel injectors are firing.

Component List
There were not many components needed for this circuit. We had two pairs of resisters with different values for each pair. The values for these resistors were calculated (calculations are shown later in the post). We had two NPN BC547 transistors. Two LED's (measured with a multimeter to be 1.7V). Lastly we had a PCB board. All these components were soldered onto a PCB board. 

The Circuit & its Calculations

As you can see from the wiring diagram we have two separate circuits. One is the control side circuit and the other is the main LED circuit. Lets talk about the transistor. The transistor has three legs, the base leg (B), the collector leg (C) and the emitter leg (E). The transistor works like a relay. It needs a low amperage to open the gate for the high amperage flow. In this case when we supply current (amperage) to the base leg, the transistor will ground that circuit with the emitter leg, as the emitter leg is wired up on the ground side of the circuit. This will then open up the gate and connect the collector leg with the emitter leg. This will allow current to flow throw the LED as the circuit is now grounded. Now as you know different components require different amount of current to operate. Using the data sheet we found out that the saturation current flow for the base side of the transistor was 0.5mA (0.005A). The base side of the transistor circuit has a 5V power supply and a resistor. The value of the resistor had to be calculated using ohms law (R = V/I). So my calculation to find out the resistor value was 4.4V divide by 0.005A. This equaled to 880Ohms. So the resistor value is 880Ohms. The reason why I used 4.4V and not 5V is because the base side of the transistor uses up 0.6V to turn on and therefore the voltage available to the circuit is 4.4V and not 5V. Now lets find out the resistor values for the LED circuit. We were given the current required by the LED to operate. It was 20mA (0.02A). The power supply on the LED circuit was 12V. But we got to keep in mind that the LED requires 1.8V to turn on and the collector side of the transistor requires about 0.2V to turn on. This means that the voltage available to the circuit is 10V. We use the same formula as above to calculate the resistance (R = V/I). My calculation was 10V divided by 0.02A, which equaled to 500ohms. The resistor values are 500ohms.  

The Two Laws Relating To This Circuit 
Ohms Law:
"Ohms Law states that the current through a conductor between two points is directly proportional to the potential difference across the two points, and inversely proportional to the resistance between them." (Wikipedia quote) The formula for this is I = V/R. This formula can be rearranged to find any of the values as long as you know two of them. 
Kirchhoff's Law:
Kirchhoff's Law states that the voltage supplied to a circuit is used up within the circuit before it reaches back to the power source (ground). Voltage supplied = Voltage used by the circuit.


Breadboard Circuit Test
Before we were allowed to make our circuit on the PCB board we had to first prove that it actually works. That's why we first build our circuit on a breadboard to see whether it actually works. This is when i encountered my first problem. The class didn't have the exact value of the resistors i needed so therefore i had to compromise. Instead of a 500ohm resister and a 880Ohm resister, i was supplied with a 470ohm resister and a 800ohm resister. This meant i had to re-calculate my current readings. The 30ohm difference from 500ohms to 470ohms only made a difference of plus 0.1mA. This meant that my LED was now going to receive 0.021A instead of 0.02A. This was a very small change and therefore was nothing to worry about. The calculation was 10V divided by 470ohms, which equaled to 0.021 (formula used was I = V/R). The same calculations were carried out for the 880ohms resistor to the 800ohms resistor. The calculation was 4.4V divided by 800ohms, which equaled to 0.0055A. The lower resistance added 0.05mA to the current flow. This change would not make a difference as it is too small to cause any damage. Also the saturation value means what is the minimum current required to turn the base side of the transistor fully on. That means a little more current is fine and wont cause any harm to the transistor. 

PCB Board
Once we proved that our circuit works on the breadboard we were allowed to make it for real on the PCB board. The PCB board is something that we haven't used before. It has rows of holes where you components can sit into and all the holes on each row are connected together (but row to row are not connected). This is why we had to put cuts in the rows to stop it from connecting to all the components. The purpose of the PCB board is for us to use these rows and and make a circuit and not use wires. Before we could lay out our components on the PCB board we had to plan it on the computer, using a program called LochMaster. This program allows you to place your components any way you want and it then allows you to check for continuity between each component. If say my resister and LED were connected together (had continuity between them), both of them would then receive 10V power supply and the voltage wont be shared. This is why we put cuts in between the components (middle of my resister and in the middle of my LED).

After our design was checked and ticked off we were allowed to place the components on the PCB board and solder the components down. When we solder the solder has to be small and shinny. A dull soldering represents a bad connection and it wont have a long life. I encountered my second problem while soldering. I bridged two components together, creating a short circuit. This would mean that my LED's wouldn't turn on and the circuit wont work. To fix this problem was easy. I used the soldering iron to break the solder in between the two components to unbridged them. This technique was showed to me by Vijay, my tutor.

Here is the pictures of my completed task

 

This is the frontal view

This is the backside view

Problems & Reflection

My main problem in completing this task was soldering. I just couldn't do a good joint soldering. My soldering sometimes even bridged two components together creating a short circuit. This was fixed as explained above. Soldering a component can be the thin line between a good connection and a bad connection. A good connection will have little solder. It will be covering the whole leg and it will be shinny. A bad connection will be having lumps of dull solder that don't even cover the entire surface of the components leg. If given the opportunity i would improve my soldering skills by practicing on a dummy PCB board. This will improve my soldering skills and it will result into a better joint connection. A bad connection can also cause resistance in the circuit. This resistance can create restriction to current flow. This will mean that the circuit will now experience a lower current flow and the voltage available to components will also decrease by a small amount, as this voltage is now required to push the current through this bad connection. This will not make much difference to the circuit but it can corrupt the circuit readings. This is why it is vital to have good connections. 

   

     

Automotive Electronics

Resisters
Resisters are electronic components that are used in various circuits. A resistor's job is very simple. It restricts the amount of current flow in a circuit. This restriction to current flow is called resistance and the value of resistance is measured in Ohms. A resistor has no positive or negative end, and therefore it can be wired up either way in a circuit. The amount of resistance caused by a resistor is determined by the colour bands on it.
Colour bands
The first couple of bands on a resistor are the units you write down.
The second to last band is the multiplier.
The last band is the tolerance of that resistor.
E.G  Say a resistor has these bands; Red, Violet, Brown and Gold. Now following the colour code chart the units are 2 (Red), 7 (Violet), 10 (Brown, also the multiplier) and 5% (Gold). The resistance of this resistor would be 265Ohms.
Here is the resistor colour code chart

 

What we did in class was first get ourselves familiar with recording the resistance of individual resistors by using the colour code chart and by using a multimeter. The multimeter was set on Ohms. The next thing we did was we chose two resistors and put them in series (one after another). We then had to calculate the total resistance and then measure it using a multimeter. When you put two resistor in a series circuit they act like one big resistor. Their resistance are added together. This was proved by out measured resistance of the two resistors. The resistors used were an 9940Ohms resistor and a 5520Ohms resistor. The total resistance measured with a multimeter was 15,490Ohms. This is the same as adding 9940 to 5520.

The third thing we had to do was to wire up the same to resistors in parallel. In a parallel circuit the total resistance of the circuit is lower than the resistance of its lowest resister. This means that the circuit's total resistance to current flow will be less than 5520 Ohms as this is the value of the circuits lowest resister. The formula for this is RT = 1/R1 + 1/R2 + 1/RN... Using this formula we calculated a resistance of 3549Ohms. But when we measured it with a multimeter the resistance came out to be 3420Ohms. The slighly lower resistance can be caused by the tolerance in the resistors.  

Diodes  

A diode is an electronic component which conducts and lets current flow through in only one direction. From Anode (positive) to Cathode (negative). There are a few different types of diodes. For our practical class we used a normal basis diode plus a LED (Light Emitting Diode). The first exercise was to measure the voltage drop over the diode. A voltage drop over a diode tells us how much voltage is required to open the diode's gate to let the current through. The voltage drop over the diode then stays constant no matter how much or how little load is applied to the circuit. The voltage drop over our diode was 0.564V and for the LED it was 1.783V. These readings were taken in forward biased direction (Anode to Cathode). In reverse biased direction (Cathode to Anode) the voltage drop reading was 0, as current cant flow through a diode backwards. To take these readings our multimeter was set on 'Diode Test Mode', The red lead was on the Anode leg of the diode and the black lead was on the Cathode leg of the diode. 

In the next exercise we had to wire up the diodes in a simple circuit. The circuit had a Vs (voltage supply) of 5V, R (resistance) of 1000 Ohms and a diode. First was our normal diode. We then had to use Ohms law and calculate the current through the circuit. The formula for this is I = V/R. Therefore the calculation was 4.4/1000 = 0.00449A (A stands for amps. Amps is the unit for current). The reason why voltage is 4.4V and not 5V is because 0.6V is used up by the diode to let the current through and therefore is subtracted from the voltage supply. The voltage available for the circuit to use is now 4.4V and not 5V. We then measured the current flow using our multimeter. To do this you have to set eh meter onto mA and then place it in series in the circuit. The measured reading was 0.0045A. We then had to measure the voltage drop over the diode. This is done the same was as explained above. Meter set on diode test mode, red lead on anode leg and black lead on cathode leg. The measured voltage drop was 0.601V. 

The Diode was then replaced by our LED. We then had to record the current flow in the circuit. The current flow had reduced from 0.0045A to 0.0030A. This is because an LED requires a higher voltage to let the current through. Therefore the voltage available to the circuit has been reduced and that's why so has the current flow. This LED required 1.8V to let the current through and that meant that the circuit only had a available voltage of 3.2V. This is why current flow was reduced in the circuit.