Glossary

15 terms that recur across the curriculum. Skim before starting; refer back as needed.

ACK

An acknowledge bit (SDA LOW on the 9th clock)

In I²C, the receiver pulls SDA LOW after a byte to acknowledge it was received.

attenuation

ADC setting that changes the measurable voltage range

Higher attenuation allows measuring higher voltages but may reduce linearity/accuracy.

deep sleep

ESP32 power mode that consumes microamps

In deep sleep, the CPU stops, RAM is lost (unless using RTC memory), and only RTC peripherals run. Wake sources include timer, GPIO, or touch.

duty cycle

Fraction of time the PWM signal is HIGH

Duty cycle controls average power: 25% duty means HIGH for 1/4 of each period.

floating

An input with no defined HIGH/LOW state

Floating inputs pick up noise and randomly flip. Always use pull-ups or pull-downs.

NACK

A no-acknowledge bit (SDA HIGH on the 9th clock)

In I²C, NACK often means 'no device responded' or 'stop sending me data'.

Ohm's Law

V = I × R (voltage equals current times resistance)

The fundamental relationship in DC circuits. If you know any two of voltage, current, or resistance, you can calculate the third.

open-drain

Outputs can pull LOW, but need pull-ups for HIGH

I²C uses open-drain so multiple devices can share a wire safely. No device actively drives HIGH; pull-up resistors do that.

power

P = V × I (watts)

Power is energy per unit time. In electronics, P = V × I. High power means heat—components have maximum power ratings.

power budget

Calculating total energy consumption over time

Sum (current × time) for each mode (active, sleep, transmit). Critical for battery-powered devices.

pull-up

A resistor that makes an input read HIGH by default

A pull-up (external or internal) prevents a GPIO input from floating. For a button-to-GND wiring, enable an internal pull-up or add ~10kΩ to 3.3V.

quantization

Rounding a continuous value into discrete steps

ADCs quantize voltages into integer codes; PWM duty also quantizes into timer steps.

RC time constant

τ = R × C (how fast a capacitor charges/discharges)

After one time constant (τ), a capacitor charges to ~63% of the final voltage. After 5τ, it's essentially fully charged.

strapping pin

A GPIO that affects boot mode on reset

Some ESP32 pins are sampled on reset to decide boot configuration. External circuits (like buttons) can accidentally force a bad boot mode.

voltage divider

Two resistors in series create a fraction of the input voltage

V_out = V_in × (R2 / (R1 + R2)). Used for level shifting, sensor scaling, and battery monitoring.