Build systems

Each system takes one build from "should I make this?" to a working circuit: the decision, the steps in order, what goes wrong, the variants, the datasheet it rests on and a one-page card to print for the bench.

Ready to build

Project system
Festival LED lights with an Arduino: a chaser, a fade and a 12 V strip
Diwali LED lights on an Arduino UNO: an 8-LED chaser at 9.1 mA per LED, a PWM fade and a 12 V strip on a logic-level MOSFET, inside the ATmega328P limits.
Printable card
Project system
555 LED flasher: two LEDs that take turns, with every value worked out
A 555 astable flashes two LEDs in turn at 0.99 Hz from a 9 V battery: 10 kΩ, 68 kΩ, 10 µF and two 470 Ω resistors, with currents, battery life and faults.
Printable card

Coming next, in order

FM transmitter, one transistor
Choosing a resistor (colour code, E-series, LED and divider)
12 V LED strip lighting: supply, wiring and dimming
Soldering your first project
Your first Arduino project (blink to button)
Power supply for a project (USB, 7805, LM317, buck)
Automatic night lamp / diya with an LDR
Reading a datasheet
DIY Wi-Fi antenna (biquad, double biquad, can, helix)
Battery-powered decorations: cells, runtime and charging

Until each one is ready, the circuits and calculators behind it are in Projects and circuits and Calculators.