[2011]
Second Year Computer Engineering
Electronics Lab
Lab 0

Second Year Computer Engineering Electronics Lab
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Color code
How can the value of a resistor be worked out from the colors of the bands?
Each color represents a number according to the following scheme:
Number Color
0 black
1 brown
2 red
3 orange
4 yellow
5 green
6 blue
7 violet
8 grey
9 white
The first band on a resistor is interpreted as the FIRST DIGIT of the resistor value. For the resistor shown below, the first band is yellow, so the first digit is
4:
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Second Year Computer Engineering Electronics Lab
Lab 0
The second band gives the SECOND DIGIT. This is a violet band, making the second digit 7. The third band is called the MULTIPLIER and is not interpreted in quite the same way. The multiplier tells you how many noughts you should write after the digits you already have. A red band tells you to add 2 noughts.
The value of this resistor is therefore 4 7 0 0 ohms, that is, 4 700 , or
4.7 . Work through this example again to confirm that you understand how to apply the color code given by the first three bands.
The remaining band is called the TOLERANCE band. This indicates the percentage accuracy of the resistor value. Most carbon film resistors have a gold-colored tolerance band, indicating that the actual resistance value is with
+ or - 5% of the nominal value. Other tolerance colors are:
Tolerance Colour
±1% brown
±2% red
±5% gold
±10% silver
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Second Year Computer Engineering Electronics Lab
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Large capacitor have the value printed plainly on them, such as 10.uF (Ten Micro
Farads) but smaller disk types along with plastic film types often have just 2 or three numbers on them.
Three ways to kill an electrolytic capacitor :
1.
Overvoltage: If the specified voltage is exceeded, current will leak through the isolation, not in a slow way that might regenerate weak areas, but violently, creating hotspots where additional break-down occurs. The danger of explosion is imminent .
2 Reversed polarity: If the applied voltage is near the normal (right polarity) working voltage, break-down is quick and violent. The effect of a low inverse voltage might be reversible .
3. Heat. Heat shortens the life of an electrolytic capacitor. A good rule of thumb is that every 10deg C over 85 will cut the life expectancy in half.
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Blocking diodes are one way valves used in electrical circuits. These are very simple devices that are often real time savers. Other than the amperage rating of the diode, there are only three basic things to remember:
1.
Cathode (side with the stripe)
2.
Anode (side without the stripe)
3. Anytime the cathode is more positive than the anode, no current will flow .
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Second Year Computer Engineering Electronics Lab
Lab 0
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An LED is the device shown above. Besides red, they can also be yellow, green and blue. The letters LED stand for Light Emitting Diode. The important thing to remember about diodes (including LEDs) is that current can only flow in one direction.
To make an LED work, you need a voltage supply and a resistor. If you try to use an
LED without a resistor, you will probably burn out the LED. The LED has very little resistance so large amounts of current will try to flow through it unless you limit the current with a resistor. If you try to use an LED without a power supply, you will be highly disappointed.
So first of all we will make our LED light up by setting up the circuit below.
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Second Year Computer Engineering Electronics Lab
Step 1: First you have to find the positive leg of the LED. The easiest way to do this is to look for the leg that is longer.
Step 2: Once you know which side is positive, put the LED on your breadboard so the positive leg is in one row and the negative leg is in another row. (In the picture below the rows are vertical.)
Step 3: Place one leg of a 330 ohm resistor (does not matter which leg) in the same row as the negative leg of the LED. Then place the other leg of the resistor in an empty row.
Step 4: Unplug the power supply adapter from the power supply. Next, put the ground
(black wire) end of the power supply adapter in the sideways row with the blue stripe beside it. Then put the positive (red wire) end of the power supply adapter in the sideways row with the red stripe beside it.
Step 5: Use a short jumper wire (use red since it will be connected to the positive voltage) to go from the positive power row (the one with the red stripe beside it) to the positive leg of the LED (not in the same hole, but in the same row). Use another short jumper wire (use black) to go from the ground row to the resistor (the leg that is not connected to the LED). Refer to the picture below if necessary.
The breadboard should look like the picture shown below.
Lab 0
Now plug the power supply into the wall and then plug the other end into the power supply adapter and the LED should light up. Current is flowing from the positive leg of the LED through the LED to the negative leg. Try turning the LED around. It should not light up. No current can flow from the negative leg of the LED to the positive leg.
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Second Year Computer Engineering Electronics Lab
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