How to wire and set a multi-function 12V delay timer relay module – choosing on-delay, off-delay or cycle mode, setting the time band, and a worked zero-code auto-off light.

The HX1838 receiver needs one Arduino pin and one library — and the IRremote v2-to-v4 change is why so much copied IR code stops working. Decode your own buttons, then drive two LEDs and a relay.

A Bluetooth RC car is a 2WD chassis, an L298N driver and an HC-05 that hands your phone’s button presses to an Arduino. Every app button sends one ASCII character, and the sketch is a switch-case that turns each character into an H-bridge state.

A complete 2WD obstacle-avoiding robot car with an Arduino Uno, L298N and HC-SR04 — from peeling the chassis film and soldering the motor tabs to the battery maths that decides whether it rolls or crawls, plus the full runnable sketch with per-motor speed trim.

An MQ-2 module tells you the air has changed, not how many ppm. Warm it up, let the Arduino learn what clean air reads, and alarm on the rise — with wiring, working code, honest calibration limits and a relay-driven exhaust fan upgrade.

An HC-SR04 measures hand distance, the Uno checks one threshold, and an SG90 servo lifts the lid — with the power split that keeps it steady.

A PIR sensor detects change in infrared, not presence — which explains both the light that never switches off and the sensor that forgets you when you stand still. Wiring, the two orange trimmers, the H/L jumper, a non-blocking sketch and the three real causes of false triggers.

A solar panel does not run your Arduino — it refills an 18650, and the cell runs the board. Panel sizing against the TP4056’s 1 A ceiling, boosting to a steady 5 V, honest weatherproofing, and the night-budget arithmetic that decides whether your project survives until dawn.

Switch a relay from your phone with the free Blynk IoT cloud and an ESP32: template and auth-token setup, three-wire relay wiring, and a sketch designed to keep working — BOOT-button override included — when the internet dies.

Wire an LCD1602 or LCD2004 with a pre-soldered I2C backpack to an Arduino Uno in four jumpers — the right library, the 0x27 vs 0x3F address scan, contrast tuning, and a symptom-by-symptom fix for blank or garbled screens.