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Cheat Sheet

Electronics All-in-One For Dummies

As you design and build with electronic circuits, you will invariably find yourself scratching your head trying to remember what color strips are on a 470 resistor or what pin on a 555 Timer IC is the trigger input. Never fear! This handy electronics Cheat Sheet will help you remember such mundane details so you can get on with the fun stuff.

Electronics Safety Rules

Safety first! Electronics is a potentially dangerous hobby. Any circuit that works with 120 VAC power from an electrical outlet is especially dangerous and could potentially kill you. Here are some safety guidelines to keep you safe as you work:

  • Never work on a circuit while power is applied.

  • Do not connect power to a circuit until the circuit is finished and you have carefully checked your work.

  • If you smell anything burning, immediately disconnect the power and examine your circuit to find out what went wrong.

  • Keep your work area dry.

  • Always wear safety goggles.

  • Be careful around large capacitors; they can continue to hold voltage long after they are disconnected from power.

  • Be especially careful when you solder because a hot soldering iron can easily burn you.

  • Always work in a well-ventilated space.

  • Have safety equipment such as a fire extinguisher, a first-aid kit, and a phone nearby.

Electronic Resistor Color Codes

Resistor values are marked with small colored stripes. The first two stripes represent numeric values and the third stripe is a multiplier. The fourth stripe gives you the resistor’s tolerance — that is, it tells you how close to the indicated value you can expect the resistance to actually be.

For example, a resistor with brown, black, orange, and gold stripes is a 10,000 whose actual resistance may vary by as much as 10%.

Color Digit Multiplier (in Ohms) Tolerance
Black 0 1 20%
Brown 1 10 1%
Red 2 100 2%
Orange 3 1 k 3%
Yellow 4 10 k 4%
Green 5 100 k
Blue 6 1 M
Violet 7 10 M
Gray 8 100 M
White 9 1,000 M
Gold 0.1 5%
Silver 0.01 10%

Ohm’s Law in Electronics

Sometimes in electronics you have no alternative but to whip out your calculator and do a little math. The most likely reason for doing this is to calculate how much resistance you need for a given situation, how much current a circuit will pull, or how much voltage will be dropped between two points in a circuit. All of these calculations can be made by using one of the following formulas derived from Ohm’s Law:

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In the above formulas, V represents voltage (in volts, naturally), I represents current (in amperes), and R represents resistance in ohms.

 

555 and 556 Timer Integrated Circuit Pinouts

The 555 is one of the most popular integrated circuits ever made. When you use it, you’ll need to be aware of the purpose of each of the eight pins in the 555 package. You may also occasionally use a 556 IC, which consists of two 555 timers in a single package. You’ll need to be aware of its pinouts as well.

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Function 555 Timer 556 First Timer 556 Second Timer
Ground 1 7 7
Trigger 2 6 8
Output 3 5 9
Reset 4 4 10
Control Voltage 5 3 11
Threshold 6 2 12
Discharge 7 1 13
Vcc 8 14 14

LM741 Op-amp Integrated Circuit Pinouts

Operational amplifiers are one of the most common types of integrated circuits. The LM741 is a popular single op-amp IC, so you should understand the purpose of each of the pins in this integrated circuit to make your electronics project run smoothly.

Pin Function
1 Not used
2 V- Inverting Input
3 V+ Non-inverting Input
4 -V Power
5 Not used
6 Vout Output
7 +V Power
8 Not used
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