Appendix G — Electronics for AVR programmers

Purpose

Connect register-level firmware to the electrical circuit it controls.

Digital inputs

A floating input has no reliable logic state. Learn pull-up/pull-down behavior, active-low wiring, input thresholds and why a button is an electrical component rather than an ideal Boolean variable.

Outputs and current

GPIO pins have electrical limits. LED current needs a resistor; loads that demand more current need a driver stage. Respect per-pin, port and device limits from the datasheet.

Drivers

Transistors/MOSFETs allow a low-current MCU signal to control a larger load. EduBoard RGB0 and BUZZ0 deliberately expose this distinction.

Debounce

Mechanical contacts bounce. Software debounce is a policy layered on physical behavior; Exercise 12 connects both.

Decoupling

Local decoupling capacitors provide a short high-frequency current path near IC supply pins. Bulk capacitance serves a different time/energy scale.

Clocks

Clock source, frequency, fuse configuration and timing calculations are linked. Timer/UART errors can originate from a wrong clock assumption.

Logic levels

TTL/CMOS MCU logic is not RS-232. Likewise, 5 V and 3.3 V systems are not automatically compatible. Identify voltage domains before connecting boards.

Analog

ADC measurements depend on reference, source impedance, noise, grounding and layout. A numeric ADC code is not automatically an accurate voltage measurement.

Habit

For every peripheral lab, draw the complete path: MCU pin → protection/driver/passive components → connector/load → return path.