Autotronics:
In this section im going to cover basics on components such as diodes, zener diodes, resistors, capacitors, and transistors on what the purpose of each component is when wired up in a circuit and show theoretical and practical tasks i've completed of each component.
Resistors:
Resistors are put into a circuit to limit current to the main component so the component does not damage.
Resistors have different colour bands on them to indicate different resistance values and tolerance levels each resistor has. their are 4 colour resistors and 5 colour band resistors.
On a 4 colour band resistor the 1st two colours represent single numbers and when put together create a 2digit number. eg. brown = 1`black = 0 so the first two bands make 10 then th 3rd band is the multiplier or in a easier way the amount of zeros you add to the 1st two bands. eg. brown = 1 black = 0 red = 2 which makes 10 plus two zeros which creates 1000, so a brown black red coloured resistor has a resistance of 1000 ohms.
the final band is the tolerance levels, the max the resistor can handle. tolerance levels usually show a silver or gold band. eg. brown = 1 black = 0 red = 2 gold = 5%
i find 5% of 1000 ohms which is 50ohms so the resistor has a positive tolerance of 1050 ohms and negative tolerance of 950 ohms.
Diodes:
there are many different types of diodes, but im specifically going to talk about the Light Emitting Diode(LED), rectifying diode and the zener diode as those are the only diodes worked with in the past weeks.
I had to try and identify the anode and cathode without using a multimeter. On a rectifying diode their is a visable grey strip which will indicate that side is the cathode and on an LED, i usually look at the length of each terminal but if each terminal was cut to an even length i wouldnt know which is which, i then discovered a groove on the plastic part of the LED which indicates that part is the cathode which therefore leaves the other side to be anode.
I was given a set value of 5volts for the power supply and 1000 ohm resistor and needed to find the amount of current that would flow through the system. Using the ohms law which is Voltage=I(amperage)xResistance i calculated 0.005amps would flow if the resistor and diode were wired up to a 5volt power supply.
Using a rectifying diode in forward bias i wired it up in a series circuit on a breadboard from a 5volt power supply with a 1000 ohm resistor and measured the current flowing through the circiut using a multimeter set on amperage and got a reading of 0.004 amps which is okay and shows the diode is working as the diode uses 0.6 volts to operate and if you take the 0.6 volts away from the supply voltage and calculate, you get rougly the same reading. Diodes are mainly used to allow current to flow one way.
Capacitor:
a capacitor is a component that charges up and stores voltage and then when the circiut is awitched off it releases the charge.
The amount of time it takes to charge the capacitor depends on the size of capacitor and size of resistor. So the equation to find the capacitors charging time is Resistance x capacitor size x 5 = charging time (RxCx5=T).
Using a 1000ohm resistor and 100uF capacitor i calculated a charge time of 500ms then checked my theory by wiring the capacitor and resistor and a switch in a parallel. Using a osilloscope i attached my circiut and it showed me the same reading in a wave form which indicated the capacitor was working at its specified range with that amount of resistance. If i had gotten a faster or slower charge time would not indicate a faulty capacitor but that i could have a bigger or smaller resistor than i thought or the capacitor was bigger which would require more charge time.
Transistors:
A transistor is put in a circiut for different reasons, they could be used to amplify voltage or used as a switch to operate another component. two types of transistors i used were the NPN and PNP type transistors. Each transistor has a base collector and emitter.
NPN transistor means it would require a positive feed to the and also positive feed to the collector. When wired in a circuit it is parallel. To allow current to flow from the emitter to the collector, enough current must flow through the base to deplete the boundary layer. When this happend current can flow through and the transistor is in operation.
The more current flowing through the base will allow more current to flow through the collector and emitter which means the transistor is in saturation and fully working. This could be indicated by a low or zero voltage drop through the collector and emitter. if a large voltage drop was found throught the collector and emitter, it indicates that their is low current flowing through the base and is semi-working. When the transistor is in this state it is in its active region. If there is not enough current through the base then the transistor will not work, this is when the transistor is in its cut-off region.
In a PNP transistor, it works similar to the NPN transistor but requires a negative feed to the base and will operate when their is zero voltage at the base.
I created a circuit using the BC547NPN transistor, 5volt power supply and two resistors to switch on an LED. One resistor i put after the LED but before the collector with a resistance of 470ohms and one resistor at the base of the transistor with a resistance of 1000 ohms. Then using a multimeter set on DC volts checked for voltage drops across the base and emitter and from the collector to the emitter and got really low readings which indicated the transistor is in saturation and this also gave off a bright light from the LED. I changed the resistor at the base to a 10,000 ohm resistor and got a much larger voltage drop from the collector to the emitter which means their is too much resistance restricting the current flow at the base and restricting current flow from the collector to the emitter. This also caused a much dimmer light glow from the LED. If too much current flows through the base from lack of resistance, this could over power and burn out the transistor.
Injector Circuit:
I recently wired up and parallel injector circuit using four resistors ,two capacitors, and to simulate injectors, used Light Emitting Diodes from a 12 volt power supply.
using a data sheet i found different tolerance levels of the capacitor. It had a max amperage level of 200 amps so i wanted to work well below that region so i dont damage the transistors. in order to do that i used the ohms law to calculate the different types of resistors i would use in the circuit.
I then wired this parallel circiut on a breadboard, but instead of have 12volt feeds to each of the base's of the two transistors, i attach seperate leads to each base of the transistors which attach to a machine that sends digital waves through the circuit and simulates the opening and closing of an injector circuit. when attached to this machine i switch on the power supply and both LED's were blinking in sync. which indicated the circuit was wired and working fine with no complications, that the resistors were at a good level allowing the right amount of current to flow through.
