Controlling Four RC Servos From Your Android Phone, Tablet, or iPhone

The EMGRobotics Audio Dual Servo Controller Board connects your iPhone/iPad or Android device to four servos (two servos for the left channel and two servos for the right channel) via the headphone jack. 

The servo controller is only 1.0" x 0.6" and comes with a 18" headphone cable. The controller can be purchased with or without a battery holder/power switch.

The servo controller is commanded using tones in the range 1000hz to 10000hz. Half the range is dedicated to controlling servo 1 while the other half is used to control servo 2. 

A jumper on the board is used to configure the servo controller in one of three modes: Differential Mode, Relative Mode, and Absolute Mode. Differential Mode is for robots using two continuous rotation servos in a differential drive configuration (one servo drives the left wheel while the other servo drives the right wheel). In Relative Mode the tones either cause the servo to turn left or turn right at speeds depending on the tone frequency. Relative Mode is ideal for camera tracking applications. Finally, Absolute Mode can be used to control the absolute position of the servo. Each tone positions the servo at a repeatable angle. this mode is ideal for robot arms or walking robots.

The Audio Dual Servo Controller Board can be purchased from

The servo controller can be commanded by any application that can generates tones in the range of 1000Hz to 10000Hz, including RFO BASIC - A BASIC interpreter for Android devices. For more information about RFO BASIC:


In addition, EMGRobotics has the Android Robot Controller a computer vision based Android application for controlling the board to track object based on color or face detection.

The EMGRobotics Robot Controller for Android can be downloaded from the Google Play store here: Google Play

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