6servo-atmel - Servo Laboratory Servo-1 Interfacing a Servo...

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Servo Laboratory Servo-1 San José State University Dept. of Mechanical and Aerospace Engineering rev. 3.0 27SEP2007 Interfacing a Servo to the Atmega 128 Purpose: To introduce the servo as a mechatronic actuator. To discover how to control the movement of a servo using the Atmega 128. To practice interfacing power electronics and switches. Components: Qty. Item 1 Atmel Atmega 128 microcontroller with STK 500 and STK 501 interface boards, and serial port cable 1 Futaba FP-S148 servo Introduction: In this lab you will explore the workings of a radio control (R/C) servo and how the Atmega 128 can be used to control one. An R/C servo consists of a dc motor, gear train, potentiometer, and some control circuitry all mounted compactly in a case. R/C servos are commonly used in radio-controlled cars, airplanes, and boats to provide limited rotational motion to steer, move control surfaces, etc. R/C servos are attractive for educational use in mechatronics, because they are relatively inexpensive (about $12- $20), they can put out about 42 oz/in of torque, they can easily be modified to produce continuous shaft rotation at relatively slow speeds, and they can easily be controlled by a microcontroller. There are three wires, white, red, and black on the servo leading from a 3-pin female connector to the case. These carry the control signal, power, and ground return respectively. Blac Red White or yellow Figure 1. R/C Servo. The R/C servo uses three wires: white carries the control signal, red carries power (usually 4.8 V to 6 V), and black is ground. Figure 2 shows how an R/C servo is made to rotate. The control circuitry inside the servo must receive a stream of pulses whose widths may vary between about 1 and 2 ms. These pulses must occur at intervals of about 10 to 20 ms. A potentiometer coupled to the rotation of the output shaft produces a voltage corresponding to the angle of the shaft. The control circuitry compares the “average” voltage of the control signal (i.e., by low pass filtering) with the voltage from the potentiometer, and the shaft rotates until the two voltages are the same. Figure 2. R/C Servo Operation.
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6servo-atmel - Servo Laboratory Servo-1 Interfacing a Servo...

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