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Chapter 2 · Watch, then practise

Hardware Design Issues

Check voltage levels and current paths before connecting software-controlled pins to real components.

3 questions · 3 with related videos. Matches are based on playlist titles; broader background matches are labeled.

What to study

  • Digital input thresholds
  • Output drive limits
  • Pull-up and pull-down resistors
  • LED current limiting

Chapter playlists

Choose a playlist

Notes

aLec11 BJT

Jonathan Valvano · 29:22 · Background lecture

Supplementary interfacing lecture; its university outline includes input/output voltage and current. Use the device limits in the answer to check compatibility.

1. Logic compatibility

Can any output called logic 1 safely drive any digital input?

No. Compare output-high and output-low guarantees with the receiving input thresholds, and check absolute voltage limits and currents. A nominal logic label does not guarantee electrical compatibility. Use an appropriate interface when the voltage domains or drive requirements differ.

Electronic Basics #16: Resistors

GreatScott! · 6:07 · Background lecture

Resistor fundamentals provide electrical background. The original chapter playlist exposes no playable entries and this title does not verify a pull-up-specific explanation.

2. Floating inputs

Why use a pull-up or pull-down with a switch input?

An open switch can leave a high-impedance input without a defined voltage. A pull resistor establishes a default logic state; closing the switch forces the other state. Its value balances noise immunity and current consumption, within the device’s electrical limits.

Electronic Basics #8: Everything about LEDs and current limiting resistors

GreatScott! · 6:28

The supplementary LED and current-limiting-resistor lesson matches this calculation; the voltage and current values here are assumed examples.

3. LED resistor calculation

Assume 3.3 V drive, 2.0 V LED drop and 2 mA target current. What resistance follows?

R = (3.3 − 2.0) / 0.002 = 650 Ω. Select an appropriate standard value and check actual output voltage, LED variation and pin-current limits. These are assumed example values, not specifications for every microcontroller or LED.

References