What this covers

A kit arrives as a bag of small objects, most of them unlabelled in any obvious way. This is how to work out what each one is and which way round it goes.

Getting this wrong is the usual way a beginner destroys a part, and it is entirely avoidable.

Before you begin

Nothing to wire. Have your components to hand, and good light. A multimeter helps for the last section but is not needed for the rest.

Resistors

Small, usually beige or blue, with a wire at each end and coloured bands around the body. They have no polarity, so either way round is fine.

The bands give the value. Hold the resistor with the lone band, usually gold or silver, on the right, then read from the left.

On a four-band resistor the first two bands are digits, the third is the multiplier and the fourth is tolerance. Red, red, brown, gold is 2, 2, times 10, which is 220 ohms: the one in nearly every LED circuit.

Five-band resistors use three digits then a multiplier. Brown, black, black, red, brown is 1, 0, 0, times 100, which is 10 kilohms.

Two honest warnings. Brown, red and orange are genuinely hard to tell apart under poor light, and on blue-bodied resistors red and orange look almost identical. And a resistor can be read from either end, giving two different answers. If the value you read seems odd for the circuit, turn it round and read it again. When it matters, measure it.

Surface-mount resistors

The tiny black rectangles on module boards are marked with numbers instead of colours. The first digits are the value and the last is how many zeros follow.

• 103 is 10 followed by 3 zeros, which is 10,000 ohms, or 10 k.
• 221 is 22 followed by 1 zero: 220 ohms.
• 472 is 47 followed by 2 zeros: 4,700 ohms, or 4.7 k.
• 000 or 0 is a link, zero ohms, used as a jumper.

This is worth knowing because it lets you read a module before trusting it. The 103 on the DHT11 board is the pull-up resistor that tutorial says you do not need to add; the markings beside each LED on the traffic light module are its current-limiting resistors.

LEDs

Clear or coloured plastic, two legs of different lengths.

• The longer leg is the anode, the positive side.
• The shorter leg is the cathode, and goes to ground.
• The rim has a flat spot on the cathode side. Trust this over leg length, because legs get trimmed.

An LED fitted backwards does not light and is not damaged. An LED fitted without a series resistor is damaged immediately. Of the two mistakes, only one costs you a part.

Capacitors

Two kinds turn up in beginner kits, and they differ in the one way that matters.

Ceramic, small orange or blue discs, no polarity, marked with a three-digit code read in picofarads the same way as surface-mount resistors. 104 is 100,000 pF, which is 100 nF, the common decoupling value.

Electrolytic, small cylinders, usually black or blue, with the value printed plainly such as 100uF 25V. These do have polarity. The negative leg is shorter and the body carries a stripe marked with minus signs down that side.

An electrolytic fitted backwards may survive, may fail quietly, or may burst. Always check the stripe. Note also the voltage rating: a 6.3 V capacitor on a 12 V supply will fail.

Transistors and voltage regulators

Both are small black semicircular or rectangular packages with three legs, and they look very similar. The printing on the flat face is the only way to tell them apart, and it is small.

Common markings in these kits: 2N2222, BC547 and S8050 are transistors; 7805 and AMS1117 are voltage regulators. Pin order differs between types and cannot be guessed, so look up the part number before wiring one.

If the printing is worn away, the part is not worth the risk. Put it aside.

Diodes

Small glass or black cylinders with a band at one end. That band marks the cathode, the end current flows towards. Diodes only conduct one way, which is the point of them, so the band is not optional information.

1N4007 is the common power diode and 1N4148 the common small-signal one.

Modules

Anything on its own small circuit board is a module, and these are the easiest of all, because the pins are labelled on the board itself.

Read the silkscreen. VCC or + is power, GND or - is ground, and the rest are signals, usually named for what they do: DO for a digital output, AO for an analog one, SDA and SCL for I2C, TRIG and ECHO on the ultrasonic sensor.

Two things to remember. The header can usually be fitted either way round, so read the label rather than counting positions. And VCC means the voltage this module wants, which is not always 5 V.

Check yourself

1. Red, red, brown, gold. What value?
2. An SMD part marked 472. What value?
3. Which LED leg goes to ground, and what is the more reliable sign?
4. You find a cylinder with a stripe down one side. What are you being told?

Answers in order: 220 ohms. 4.7 kilohms. The shorter one, and the flat on the rim is more reliable than leg length. That it is polarised, and the striped side is negative.

Troubleshooting

Next steps

• Easier first: Voltage, Current and Resistance.
• Next: Using a Breadboard, where these parts get connected together.
• Related product: a digital multimeter, which settles every doubt on this page in seconds.

Sources and attribution

All text in this tutorial is original Siratek work.

• Resistor and capacitor marking schemes are the standard published codes.
• Part numbers are given as examples of what commonly appears in these kits, and any specific part should be confirmed against its own datasheet.

No third-party tutorial text, diagrams, photographs or code has been reproduced here.