Amazon.com: WYPH Ultrasonic Module HC-SR04 Distance Measuring Ranging Sensor for Arduino UNO for Mega R3 Duemilanove Nano Robot Pack of 10pcs : Industrial & Scientific
Smraza 5pcs Ultrasonic Module HC-SR04 Distance Sensor with 2pcs Mounting Bracket for Arduino R3 MEGA Mega2560 Duemilanove Nano Robot XBee ZigBee: Amazon.com: Industrial & Scientific
Amazon.com: ACEIRMC HC-SR04 Ultrasonic Sensor Distance Module for Nano Robot XBee ZigBee by ElecRight(5pcs : Industrial & Scientific