Cheat Sheet

Electronics All-in-One For Dummies Cheat Sheet

From Electronics All-in-One For Dummies, 2nd Edition

By Doug Lowe

As you design and use electronic circuits, you invariably find yourself scratching your head trying to remember what color stripes are on a 470 resistor or what pin on a 555 Timer IC is the trigger input. Never fear! This handy Cheat Sheet helps you remember such mundane details — plus the decidedly not mundane but essential safety info — so that you can get on with the fun stuff, efficiently and safely.

Staying Safe: Electronics Safety Rules

Safety first! Electronics is a potentially dangerous hobby. Any circuit that works with 230 VAC power from an electrical outlet is especially dangerous and can kill you. Here are some basic safety guidelines to keep you safe while you work:

  • Never work on a circuit while power is applied.

  • Don’t connect power to a circuit until the circuit is finished and you’ve checked your work carefully.

  • 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’re disconnected from power.

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

  • Always work in a well-ventilated space.

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

Remembering Electronic Resistor Colour Codes

Resistor values are marked with small coloured 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 be.

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

Here’s the full list to keep handy:

Colour 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
Grey 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 maths. The most likely reason is to calculate how much resistance you need for a given situation, how much current a circuit is going to pull or how much voltage will be dropped between two points in a circuit.

You can make all these calculations by using one of the following formulas derived from Ohm’s law:






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 (ICs) ever made. When you use it, you 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, and the same applies to knowing its pinouts as well.

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

Understanding LM741 Op-Amp Integrated Circuit Pinouts

Operational amplifiers are one of the most common types of IC. The LM741 is a popular single op-amp IC, and you need to understand the purpose of each of its pins to make your electronics projects 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