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Servo Motor
Figure 5-2. An Arduino-based servo motor control system block diagram
Flexiforce Sensor
Arduino Servo Motor
Figure 5-3. A remixed FlexiForce sensor-activated servo motor control system block diagram
Figure 5-4. An Arduino-based stepper motor control system block diagram
Figure 5-5. A remixed FlexiForce sensor-activated servo motor control system block diagram
How It Works
As discussed in Chapter 4, transistors and electromechanical relays are used as direct electronic circuit drivers to control medium-to-heavy current-drawn electrical loads. With the aid of the Arduino’s ATmega328 microcontroller, digitally operated motors like a servo and stepper can be controlled quite easily. Referencing the block diagram in Figure 5-6, to operate a servo motor digitally, an output port pin from the ATmega328 microcontroller drives the command control signal lead of the electromechanical component. The command control signal lead receives digital data in the form of pulses that correlate to the angle in which the servo motor will rotate. The pulse has a specific ON time duration that represents an angle. For example, the starting or neutral position to command the servo motor is 1.5ms. An angle of 0° is accomplish using a 1.25ms pulse. To rotate the servo motor to 180° a 1.75ms pulse from the Arduino is needed. Figure 5-7 shows the primary pulses and the angular position of the servo motor.
Figure 5-6. An Arduino-based computing platform used to control a servo motor
Figure 5-7. Typical pulse widths with angular positions for controlling a servo motor
Experimenting with a Servo Motor
The Arduino computational platform provides the command control signal (PCM) to drive a typical servo motor. A servo motor is an electromechanical device that uses error-sensing negative feedback to correct the operation of a mechanism. Negative feedback is a small amount of energy taken from a voltage- or current-detecting component and looping it back for proper adjustment to the error-correcting device. In Figure 5-6, the circuit schematic diagram consists of the Arduino and the servo motor illustrated in Figure 5-8. When you upload the sketch in Listing 5-1, the servo motor starts a sweep from neutral position to 180° and back to its original starting point. This motion is continuous, which allows the Arduino to be an automated tester for other suspect servo motors.
The servo motor wiring to the Arduino is quite simple. The wiring consists of the command control signal wire of the servo motor going to D9 of the Arduino PCB. The brown wire goes to ground with the red wire terminating at the +5VDC on the board. A wiring alternative is to use a solderless breadboard for the servo-to- Arduino connections, as shown in Figure 5-9 on the Fritzing circuit build.
Figure 5-8. Controlling a servo motor with an Arduino
Figure 5-9. Fritzing circuit build of an Arduino-based servo motor controller
Fritzing Software
The Fritzing circuit build serves as prototype guide for the actual construction of the Arduino-based servo motor controller. Although the prototyping tools used by the author are slightly different, the wiring shown in Figure 5-9 is quite similar to the actual build. Figure 5-10 shows the prototype of the servo motor controller. The process of designing a product virtually using graphics or modeling software and then building with real components is practiced daily in electronics manufacturing. Fritzing software is free and provides a wealth of resources online for taking a solderless prototype and turning it into a functional PCB-based product. So if you are a hobbyist, a student, an artist, or even a professional engineer, Fritzing software lets you adopt an electronics design automation (EDA) approach to your Arduino projects. The library of parts is quite substantial and provides technical resource for learning electronics with the Arduino.