Forge — From idea to product

Slide 1

Why units matter

Every measurement in electronics is a number plus a unit. "10" doesn't tell you anything; "10 V" tells you everything. The unit is the difference between specifying a battery and specifying a phone charger.

What units do for you

Three things, mostly:

Make the number meaningful. "4.7" could be 4.7 ohms, 4.7 kilohms, 4.7 megohms — three resistors that behave nothing like each other.
Let you check your work. If you're computing power and end up with units of "volts × volts ÷ ohms", something is wrong. Right answer: V²/Ω = watts. Units catch errors before maths does.
Let you read every datasheet on Earth. The whole industry uses the same units. A part from Texas Instruments and a part from Microchip share the same volts, amperes, ohms.

What's coming in this lesson

Two slides:

SI prefixes — k (kilo), M (mega), G (giga), m (milli), µ (micro), n (nano). The factor-of-1000 jumps that turn "47000 Ω" into "47 k", "0.000022 F" into "22 µF".
The five electronics units you'll use daily — volts, amperes, ohms, farads, henries.

Get these two slides solid and you can read 90% of any schematic, BOM, or datasheet.

Slide 2

Prefixes you'll see daily: k, M, G, m, µ, n

Electronics values span a huge range — picofarads to amps, microseconds to days. SI prefixes are how the industry writes "10⁻⁶" without making you read it as "ten to the negative sixth". You'll see six prefixes again and again.

The six you'll meet daily

Prefix	Symbol	Factor	What it looks like
giga	G	× 10⁹	2.4 GHz Wi-Fi signal
mega	M	× 10⁶	1 MΩ pull-up resistor
kilo	k	× 10³	10 kΩ pull-up, 5 kbps comms
milli	m	× 10⁻³	5 mA LED current, 100 ms delay
micro	µ	× 10⁻⁶	22 µF capacitor, 10 µs ADC sample
nano	n	× 10⁻⁹	100 nF decoupling cap, 50 ns rise time

How to read them

The prefix multiplies the bare unit. So:

10 kΩ = 10 × 1,000 Ω = 10,000 ohms
22 µF = 22 × 0.000001 F = 0.000022 farads
3.3 V = 3.3 volts (no prefix; just volts)
50 mA = 0.050 amperes

The ones that trip people up

Two things to watch for:

'M' vs 'm'. Capital M is mega (million); lowercase m is milli (thousandth). A 1 MΩ resistor and a 1 mΩ resistor are off by a factor of a billion. Case matters.
'µ' vs 'u'. The proper symbol is µ (Greek lowercase mu), but typed casually as 'u' or 'uF'. They mean the same thing — micro. A common convention is to use µ where the font supports it and u where it doesn't.

You don't need to memorise this whole table on day one. You'll use these every day on the lab bench and they'll stick. The point of this slide is recognising them when you see them.

Quick check

A datasheet lists a resistor as 4.7k. What's the resistance in ohms?

Slide 3

Electronics units: V, A, Ω, F, H

Five units cover almost everything you'll measure in electronics for the first year. Memorise these and you can read almost any datasheet.

The five

Quantity	Unit	Symbol	Common appearance
Voltage	volt	V	3.3 V, 12 V, 230 V mains
Current	ampere ("amp")	A	5 mA LED, 2 A battery charger
Resistance	ohm	Ω	10 kΩ pull-up, 100 Ω current-limit
Capacitance	farad	F	22 µF, 100 nF
Inductance	henry	H	10 µH choke, 1 mH inductor

The one law you'll cite the most

Voltage, current, and resistance are tied together by Ohm's Law:

V = I × R

In words: voltage equals current times resistance. Two practical uses:

Sizing a current-limit resistor. An LED needs 20 mA at 2 V. Your supply is 5 V. The resistor has to drop (5 − 2) = 3 V at 20 mA, so R = 3 V / 0.020 A = 150 Ω.
Predicting current. A 1 kΩ resistor across 5 V will pass I = V/R = 5 / 1000 = 0.005 A = 5 mA.

You'll do this calculation hundreds of times. Worth burning into memory.

Power

Voltage and current together give power, measured in watts (W):

P = V × I

A 5 V phone charger drawing 2 A delivers 10 W. A 12 V LED strip drawing 1.5 A is using 18 W. Power matters because that's what your power supply has to provide and what your heatsink has to dissipate.

These five units, with the two equations, cover the foundation of every electronic product. The rest of the technical ladder builds on this.