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.