Paso 1: materiales
Todo lo que realmente necesitas es:
1. un protoboard (http://www.amazon.com/Solderless-BreadBoard-tie-points-power-rails/dp/B005GYAIES/ref=sr_1_1?ie=UTF8 & qid = 1442695282 & sr = 8-1 & keywords = protoboard)
2. un Arduino de cualquier tipo (usé un Uno) (http://www.amazon.com/Arduino-UNO-board-DIP-ATmega328P/dp/B006H06TVG/ref=sr_1_1?s=electronics & ie = UTF8 & qid = 1442695333 & sr = 1-1 & keywords = arduino + uno)
3. módulo relé (http://www.amazon.com/Indicator-Light-Channel-Module-Arduino/dp/B00P7QDJD2/ref=sr_1_5?s=electronics & ie = UTF8 & qid = 1442695315 & sr = 1-5 & keywords = relé + módulo)
4. un sensor SR04 ultrasónico (http://www.amazon.com/niceEshop-Ultrasonic-Distance-Measuring-Sensor/dp/B00F167T2A/ref=sr_1_4?s=electronics & ie = UTF8 & qid = 1442695299 & sr = 1-4 & keywords = sr04 + distancia)
5. los cables puente (http://www.amazon.com/Wosang-Solderless-Flexible-Breadboard-Jumper/dp/B005TZJ0AM/ref=sr_1_2?s=electronics & ie = UTF8 & qid = 1442695342 & sr = 1-2 & keywords = puente + cables)