What is a Resistor?
A resistor is a component that limits the flow of electrical current — the plumbing valve of electronics. It's the most common part in any circuit, and in this kit it plays two roles: protecting components (LEDs) and shaping signals (pull-downs and voltage dividers).
Ohm's Law
The one equation behind everything you'll build:
V = I × R — voltage = current × resistance
Rearranged: I = V / R and R = V / I
Two worked examples straight from your kit:
- LED circuit (Day 2): 5V supply − 2V LED drop = 3V across a 220Ω resistor → I = 3 / 220 ≈ 14mA. Bright and safe.
- Pull-down (Day 3): switch ON puts 5V across a 10kΩ resistor → I = 5 / 10,000 = 0.5mA. Practically free.
Reading the Color Bands
Four bands: first two are digits, third is the multiplier, fourth is tolerance.
| Color | Digit | Multiplier | |-------|-------|-----------| | Black | 0 | ×1 | | Brown | 1 | ×10 | | Red | 2 | ×100 | | Orange | 3 | ×1,000 | | Yellow | 4 | ×10,000 | | Green | 5 | ×100,000 | | Blue | 6 | ×1,000,000 | | Violet | 7 | — | | Gray | 8 | — | | White | 9 | — | | Gold | — | tolerance ±5% |
Hold the resistor with the gold band on the right, then read left to right.
Your Kit's Three Values
| Value | Bands | Where you'll use it | |-------|-------|---------------------| | 220Ω | Red-Red-Brown-Gold | Current limiting for single LEDs (Days 2–4) | | 330Ω | Orange-Orange-Brown-Gold | Current limiting for the RGB LED legs (Day 14) | | 10kΩ | Brown-Black-Orange-Gold | Pull-downs for DIP switches (Days 3–4) and the photoresistor voltage divider (Days 6–7) |
What's a Pull-Down?
A digital input pin that isn't connected to anything doesn't read LOW — it floats, picking up electrical noise like a tiny antenna and reading random HIGH/LOW garbage. A pull-down resistor (10kΩ from the pin to GND) drains that noise away so the pin reads a solid LOW until the switch actually connects it to 5V. Every DIP switch in the missions is wired this way — that's why ON reads HIGH reliably.
Why 10kΩ and not a plain wire? A wire to GND would short 5V straight to ground the moment you flip the switch. 10kΩ is small enough to hold the pin LOW but big enough that switch-ON only wastes half a milliamp.
Power Rating
Your kit's resistors are rated ¼ watt (0.25W). Power dissipated = I² × R. The hottest-running resistor in any mission is the LED's 220Ω at about 0.014² × 220 ≈ 0.04W — barely a sixth of the rating. Nothing in this course will ever cook a resistor.
Combining Resistors
- In series, values add: 220Ω + 330Ω = 550Ω
- In parallel, resistance drops: two 220Ω side by side = 110Ω
You won't need this for the missions, but it's how you improvise a value you don't have.
Tips
- Resistors are not polarized — either direction works
- When in doubt, go bigger: a too-large resistor means a dim LED; a too-small one means a dead LED
- Colors hard to read? Measure with a multimeter set to Ω
- The exact value isn't sacred — resistors are ±5%, and a 220Ω vs 330Ω LED difference is barely visible