Schematic: Arduino Transmitter

RF 433MHz module:
tx_pin --> pin 3
HC-SR04 module:
trig_pin --> pin 5
echo_pin --> pin 6

Schematic: Arduino Yun Receiver

RF 433MHz module:
rx_pin --> pin 3
TrafficLight (3 LEDs):
RedLED --> pin 5
OrangeLED --> pin 6
GreenLED --> pin 7

DS3231 (Real-Time-Clock):
SCL --> SCL (pin 3 on Arduino Yun)
SDA --> SDA (pin 2 on Arduino Yun)

Code

CONTINUED TO BOOK PART 2 ...