Java - Servo Brick – Tinkerforge

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# Java - Servo Brick

This is the description of the Java API bindings for the Servo Brick. General information and technical specifications for the Servo Brick are summarized in its hardware description.

An installation guide for the Java API bindings is part of their general description.

## Examples

The example code below is Public Domain (CC0 1.0).

### Configuration

Download (ExampleConfiguration.java)

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    import com.tinkerforge.BrickServo;
    import com.tinkerforge.IPConnection;

    public class ExampleConfiguration {
        private static final String HOST = "localhost";
        private static final int PORT = 4223;
        private static final String UID = "a4LCMm3K2bS"; // Change to your UID

        // Note: To make the example code cleaner we do not handle exceptions. Exceptions you
        //       might normally want to catch are described in the documentation
        public static void main(String args[]) throws Exception {
            IPConnection ipcon = new IPConnection(); // Create IP connection
            BrickServo servo = new BrickServo(UID, ipcon); // Create device object

            ipcon.connect(HOST, PORT); // Connect to brickd
            // Don't use device before ipcon is connected

            // Configure two servos with voltage 5.5V
            // Servo 1: Connected to port 0, period of 19.5ms, pulse width of 1 to 2ms
            //          and operating angle -100 to 100°
            //
            // Servo 2: Connected to port 5, period of 20ms, pulse width of 0.95
            //          to 1.95ms and operating angle -90 to 90°
            servo.setOutputVoltage(5500);

            servo.setDegree((short)0, (short)-10000, (short)10000);
            servo.setPulseWidth((short)0, 1000, 2000);
            servo.setPeriod((short)0, 19500);
            servo.setAcceleration((short)0, 1000); // Slow acceleration
            servo.setVelocity((short)0, 0xFFFF); // Full speed

            servo.setDegree((short)5, (short)-9000, (short)9000);
            servo.setPulseWidth((short)5, 950, 1950);
            servo.setPeriod((short)5, 20000);
            servo.setAcceleration((short)5, 0xFFFF); // Full acceleration
            servo.setVelocity((short)5, 0xFFFF); // Full speed

            servo.setPosition((short)0, (short)10000); // Set to most right position
            servo.enable((short)0);

            servo.setPosition((short)5, (short)-9000); // Set to most left position
            servo.enable((short)5);

            System.out.println("Press key to exit"); System.in.read();
            ipcon.disconnect();
        }
    }

### Callback

Download (ExampleCallback.java)

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    import com.tinkerforge.BrickServo;
    import com.tinkerforge.IPConnection;
    import com.tinkerforge.TinkerforgeException;

    public class ExampleCallback {
        private static final String HOST = "localhost";
        private static final int PORT = 4223;
        private static final String UID = "a4LCMm3K2bS"; // Change to your UID

        // Note: To make the example code cleaner we do not handle exceptions. Exceptions you
        //       might normally want to catch are described in the documentation
        public static void main(String args[]) throws Exception {
            IPConnection ipcon = new IPConnection(); // Create IP connection
            // Note: Declare servo final, so the listener can access it
            final BrickServo servo = new BrickServo(UID, ipcon); // Create device object

            ipcon.connect(HOST, PORT); // Connect to brickd
            // Don't use device before ipcon is connected

            // Add and implement position reached listener
            // (called if velocity set by setVelocity is reached)
            servo.addPositionReachedListener(new BrickServo.PositionReachedListener() {
                public void positionReached(short servoNum, short position) {
                    if(position == 9000) {
                        System.out.println("Position: 90°, going to -90°");
                        try {
                            servo.setPosition(servoNum, (short)-9000);
                        } catch(TinkerforgeException e) {
                        }
                    } else if(position == -9000) {
                        System.out.println("Position: -90°, going to 90°");
                        try {
                            servo.setPosition(servoNum, (short)9000);
                        } catch(TinkerforgeException e) {
                        }
                    } else {
                        // Can only happen if another program sets velocity
                        System.out.println("Error");
                    }
                }
            });

            servo.enablePositionReachedCallback();

            // Set velocity to 100°/s. This has to be smaller or equal to the
            // maximum velocity of the servo you are using, otherwise the
            // velocity reached listener will be called too early
            servo.setVelocity((short)0, 10000);
            servo.setPosition((short)0, (short)9000);
            servo.enable((short)0);

            System.out.println("Press key to exit"); System.in.read();
            ipcon.disconnect();
        }
    }

## API

Generally, every method of the Java bindings that returns a value can throw a `TimeoutException`. This exception gets thrown if the device did not respond. If a cable based connection is used, it is unlikely that this exception gets thrown (assuming nobody unplugs the device). However, if a wireless connection is used, timeouts will occur if the distance to the device gets too big.

Beside the `TimeoutException` there is also a `NotConnectedException` that is thrown if a method needs to communicate with the device while the IP Connection is not connected.

Since Java does not support multiple return values and return by reference is not possible for primitive types, we use small classes that only consist of member variables. The member variables of the returned objects are described in the corresponding method descriptions.

The package for all Brick/Bricklet bindings and the IP Connection is `com.tinkerforge.*`

All methods listed below are thread-safe.

Every function of the Servo Brick API that has a servo_num parameter can address a servo with the servo number (0 to 6). If it is a setter function then multiple servos can be addressed at once with a bitmask for the servos, if the highest bit is set. For example: `1` will address servo 1, `(1 << 1) | (1 << 5) | (1 << 7)` will address servos 1 and 5, `0xFF` will address all seven servos, etc. This allows to set configurations to several servos with one function call. It is guaranteed that the changes will take effect in the same PWM period for all servos you specified in the bitmask.

### Basic Functions

public class `BrickServo`(String uid, IPConnection ipcon)

  Creates an object with the unique device ID `uid`:

      BrickServo servo = new BrickServo("YOUR_DEVICE_UID", ipcon);

  This object can then be used after the IP Connection is connected (see examples above).

public void `enable`(short servoNum)

  Enables a servo (0 to 6). If a servo is enabled, the configured position, velocity, acceleration, etc. are applied immediately.

public void `disable`(short servoNum)

  Disables a servo (0 to 6). Disabled servos are not driven at all, i.e. a disabled servo will not hold its position if a load is applied.

public boolean `isEnabled`(short servoNum)

  Returns true if the specified servo is enabled, false otherwise.

public void `setPosition`(short servoNum, short position)

  Sets the position in °/100 for the specified servo.

  The default range of the position is -9000 to 9000, but it can be specified according to your servo with `setDegree()`.

  If you want to control a linear servo or RC brushless motor controller or similar with the Servo Brick, you can also define lengths or speeds with `setDegree()`.

public short `getPosition`(short servoNum)

  Returns the position of the specified servo as set by `setPosition()`.

public short `getCurrentPosition`(short servoNum)

  Returns the current position of the specified servo. This may not be the value of `setPosition()` if the servo is currently approaching a position goal.

public void `setVelocity`(short servoNum, int velocity)

  Sets the maximum velocity of the specified servo in °/100s. The velocity is accelerated according to the value set by `setAcceleration()`.

  The minimum velocity is 0 (no movement) and the maximum velocity is 65535. With a value of 65535 the position will be set immediately (no velocity).

  The default value is 65535.

public int `getVelocity`(short servoNum)

  Returns the velocity of the specified servo as set by `setVelocity()`.

public int `getCurrentVelocity`(short servoNum)

  Returns the current velocity of the specified servo. This may not be the value of `setVelocity()` if the servo is currently approaching a velocity goal.

public void `setAcceleration`(short servoNum, int acceleration)

  Sets the acceleration of the specified servo in °/100s².

  The minimum acceleration is 1 and the maximum acceleration is 65535. With a value of 65535 the velocity will be set immediately (no acceleration).

  The default value is 65535.

public int `getAcceleration`(short servoNum)

  Returns the acceleration for the specified servo as set by `setAcceleration()`.

public void `setOutputVoltage`(int voltage)

  Sets the output voltages with which the servos are driven in mV. The minimum output voltage is 2000mV and the maximum output voltage is 9000mV.

  Note

  We recommend that you set this value to the maximum voltage that is specified for your servo, most servos achieve their maximum force only with high voltages.

  The default value is 5000.

public int `getOutputVoltage`()

  Returns the output voltage as specified by `setOutputVoltage()`.

public void `setPulseWidth`(short servoNum, int min, int max)

  Sets the minimum and maximum pulse width of the specified servo in µs.

  Usually, servos are controlled with a PWM, whereby the length of the pulse controls the position of the servo. Every servo has different minimum and maximum pulse widths, these can be specified with this function.

  If you have a datasheet for your servo that specifies the minimum and maximum pulse width, you should set the values accordingly. If your servo comes without any datasheet you have to find the values via trial and error.

  Both values have a range from 1 to 65535 (unsigned 16-bit integer). The minimum must be smaller than the maximum.

  The default values are 1000µs (1ms) and 2000µs (2ms) for minimum and maximum pulse width.

public BrickServo.PulseWidth `getPulseWidth`(short servoNum)

  Returns the minimum and maximum pulse width for the specified servo as set by `setPulseWidth()`.

  The returned object has the public member variables `int min` and `int max`.

public void `setDegree`(short servoNum, short min, short max)

  Sets the minimum and maximum degree for the specified servo (by default given as °/100).

  This only specifies the abstract values between which the minimum and maximum pulse width is scaled. For example: If you specify a pulse width of 1000µs to 2000µs and a degree range of -90° to 90°, a call of `setPosition()` with 0 will result in a pulse width of 1500µs (-90° = 1000µs, 90° = 2000µs, etc.).

  Possible usage:

  - The datasheet of your servo specifies a range of 200° with the middle position at 110°. In this case you can set the minimum to -9000 and the maximum to 11000.
  - You measure a range of 220° on your servo and you don't have or need a middle position. In this case you can set the minimum to 0 and the maximum to 22000.
  - You have a linear servo with a drive length of 20cm, In this case you could set the minimum to 0 and the maximum to 20000. Now you can set the Position with `setPosition()` with a resolution of cm/100. Also the velocity will have a resolution of cm/100s and the acceleration will have a resolution of cm/100s².
  - You don't care about units and just want the highest possible resolution. In this case you should set the minimum to -32767 and the maximum to 32767.
  - You have a brushless motor with a maximum speed of 10000 rpm and want to control it with a RC brushless motor controller. In this case you can set the minimum to 0 and the maximum to 10000. `setPosition()` now controls the rpm.

  Both values have a possible range from -32767 to 32767 (signed 16-bit integer). The minimum must be smaller than the maximum.

  The default values are -9000 and 9000 for the minimum and maximum degree.

public BrickServo.Degree `getDegree`(short servoNum)

  Returns the minimum and maximum degree for the specified servo as set by `setDegree()`.

  The returned object has the public member variables `short min` and `short max`.

public void `setPeriod`(short servoNum, int period)

  Sets the period of the specified servo in µs.

  Usually, servos are controlled with a PWM. Different servos expect PWMs with different periods. Most servos run well with a period of about 20ms.

  If your servo comes with a datasheet that specifies a period, you should set it accordingly. If you don't have a datasheet and you have no idea what the correct period is, the default value (19.5ms) will most likely work fine.

  The minimum possible period is 1µs and the maximum is 65535µs.

  The default value is 19.5ms (19500µs).

public int `getPeriod`(short servoNum)

  Returns the period for the specified servo as set by `setPeriod()`.

public int `getServoCurrent`(short servoNum)

  Returns the current consumption of the specified servo in mA.

public int `getOverallCurrent`()

  Returns the current consumption of all servos together in mA.

public int `getStackInputVoltage`()

  Returns the stack input voltage in mV. The stack input voltage is the voltage that is supplied via the stack, i.e. it is given by a Step-Down or Step-Up Power Supply.

public int `getExternalInputVoltage`()

  Returns the external input voltage in mV. The external input voltage is given via the black power input connector on the Servo Brick.

  If there is an external input voltage and a stack input voltage, the motors will be driven by the external input voltage. If there is only a stack voltage present, the motors will be driven by this voltage.

  Warning

  This means, if you have a high stack voltage and a low external voltage, the motors will be driven with the low external voltage. If you then remove the external connection, it will immediately be driven by the high stack voltage

### Advanced Functions

public short[] `getAPIVersion`()

  Returns the version of the API definition (major, minor, revision) implemented by this API bindings. This is neither the release version of this API bindings nor does it tell you anything about the represented Brick or Bricklet.

public boolean `getResponseExpected`(short functionId)

  Returns the response expected flag for the function specified by the function ID parameter. It is true if the function is expected to send a response, false otherwise.

  For getter functions this is enabled by default and cannot be disabled, because those functions will always send a response. For listener configuration functions it is enabled by default too, but can be disabled by `setResponseExpected()`. For setter functions it is disabled by default and can be enabled.

  Enabling the response expected flag for a setter function allows to detect timeouts and other error conditions calls of this setter as well. The device will then send a response for this purpose. If this flag is disabled for a setter function then no response is send and errors are silently ignored, because they cannot be detected.

  See `setResponseExpected()` for the list of function ID constants available for this function.

public void `setResponseExpected`(short functionId, boolean responseExpected)

  Changes the response expected flag of the function specified by the function ID parameter. This flag can only be changed for setter (default value: false) and listener configuration functions (default value: true). For getter functions it is always enabled and listeners it is always disabled.

  Enabling the response expected flag for a setter function allows to detect timeouts and other error conditions calls of this setter as well. The device will then send a response for this purpose. If this flag is disabled for a setter function then no response is send and errors are silently ignored, because they cannot be detected.

  The following function ID constants are available for this function:

  - BrickServo.FUNCTION_ENABLE = 1
  - BrickServo.FUNCTION_DISABLE = 2
  - BrickServo.FUNCTION_SET_POSITION = 4
  - BrickServo.FUNCTION_SET_VELOCITY = 7
  - BrickServo.FUNCTION_SET_ACCELERATION = 10
  - BrickServo.FUNCTION_SET_OUTPUT_VOLTAGE = 12
  - BrickServo.FUNCTION_SET_PULSE_WIDTH = 14
  - BrickServo.FUNCTION_SET_DEGREE = 16
  - BrickServo.FUNCTION_SET_PERIOD = 18
  - BrickServo.FUNCTION_SET_MINIMUM_VOLTAGE = 24
  - BrickServo.FUNCTION_ENABLE_POSITION_REACHED_CALLBACK = 29
  - BrickServo.FUNCTION_DISABLE_POSITION_REACHED_CALLBACK = 30
  - BrickServo.FUNCTION_ENABLE_VELOCITY_REACHED_CALLBACK = 32
  - BrickServo.FUNCTION_DISABLE_VELOCITY_REACHED_CALLBACK = 33
  - BrickServo.FUNCTION_ENABLE_STATUS_LED = 238
  - BrickServo.FUNCTION_DISABLE_STATUS_LED = 239
  - BrickServo.FUNCTION_RESET = 243

public void `setResponseExpectedAll`(boolean responseExpected)

  Changes the response expected flag for all setter and listener configuration functions of this device at once.

public void `enableStatusLED`()

  Enables the status LED.

  The status LED is the blue LED next to the USB connector. If enabled is is on and it flickers if data is transfered. If disabled it is always off.

  The default state is enabled.

  New in version 2.3.1 (Firmware).

public void `disableStatusLED`()

  Disables the status LED.

  The status LED is the blue LED next to the USB connector. If enabled is is on and it flickers if data is transfered. If disabled it is always off.

  The default state is enabled.

  New in version 2.3.1 (Firmware).

public boolean `isStatusLEDEnabled`()

  Returns true if the status LED is enabled, false otherwise.

  New in version 2.3.1 (Firmware).

public BrickServo.Protocol1BrickletName `getProtocol1BrickletName`(char port)

  Returns the firmware and protocol version and the name of the Bricklet for a given port.

  This functions sole purpose is to allow automatic flashing of v1.x.y Bricklet plugins.

  The returned object has the public member variables `short protocolVersion`, `short[] firmwareVersion` and `String name`.

public short `getChipTemperature`()

  Returns the temperature in °C/10 as measured inside the microcontroller. The value returned is not the ambient temperature!

  The temperature is only proportional to the real temperature and it has an accuracy of +-15%. Practically it is only useful as an indicator for temperature changes.

public void `reset`()

  Calling this function will reset the Brick. Calling this function on a Brick inside of a stack will reset the whole stack.

  After a reset you have to create new device objects, calling functions on the existing ones will result in undefined behavior!

public BrickServo.Identity `getIdentity`()

  Returns the UID, the UID where the Brick is connected to, the position, the hardware and firmware version as well as the device identifier.

  The position can be '0'-'8' (stack position).

  The device identifier numbers can be found here. There is also a constant for the device identifier of this Brick.

  The returned object has the public member variables `String uid`, `String connectedUid`, `char position`, `short[] hardwareVersion`, `short[] firmwareVersion` and `int deviceIdentifier`.

### Listener Configuration Functions

public void `setMinimumVoltage`(int voltage)

  Sets the minimum voltage in mV, below which the `UnderVoltageListener` listener is triggered. The minimum possible value that works with the Servo Brick is 5V. You can use this function to detect the discharge of a battery that is used to drive the stepper motor. If you have a fixed power supply, you likely do not need this functionality.

  The default value is 5V (5000mV).

public int `getMinimumVoltage`()

  Returns the minimum voltage as set by `setMinimumVoltage()`

public void `enablePositionReachedCallback`()

  Enables the `PositionReachedListener` listener.

  Default is disabled.

  New in version 2.0.1 (Firmware).

public void `disablePositionReachedCallback`()

  Disables the `PositionReachedListener` listener.

  Default is disabled.

  New in version 2.0.1 (Firmware).

public short `isPositionReachedCallbackEnabled`()

  Returns true if `PositionReachedListener` listener is enabled, false otherwise.

  New in version 2.0.1 (Firmware).

public void `enableVelocityReachedCallback`()

  Enables the `VelocityReachedListener` listener.

  Default is disabled.

  New in version 2.0.1 (Firmware).

public void `disableVelocityReachedCallback`()

  Disables the `VelocityReachedListener` listener.

  Default is disabled.

  New in version 2.0.1 (Firmware).

public short `isVelocityReachedCallbackEnabled`()

  Returns true if `VelocityReachedListener` listener is enabled, false otherwise.

  New in version 2.0.1 (Firmware).

### Listeners

Listeners can be registered to receive time critical or recurring data from the device. The registration is done with "add*Listener" functions of the device object.

The parameter is a listener class object, for example:

    device.addExampleListener(new BrickServo.ExampleListener() {
        public void property(int value) {
            System.out.println("Value: " + value);
        }
    });

The available listener classes with inherent methods to be overwritten are described below. It is possible to add several listeners and to remove them with the corresponding "remove*Listener" function.

Note

Using listeners for recurring events is always preferred compared to using getters. It will use less USB bandwidth and the latency will be a lot better, since there is no round trip time.

public class `BrickServo.UnderVoltageListener`()

  This listener can be added with the `addUnderVoltageListener()` function. An added listener can be removed with the `removeUnderVoltageListener()` function.

  public void `underVoltage`(int voltage)

    This listener is triggered when the input voltage drops below the value set by `setMinimumVoltage()`. The parameter is the current voltage given in mV.

public class `BrickServo.PositionReachedListener`()

  This listener can be added with the `addPositionReachedListener()` function. An added listener can be removed with the `removePositionReachedListener()` function.

  public void `positionReached`(short servoNum, short position)

    This listener is triggered when a position set by `setPosition()` is reached. The parameters are the servo and the position that is reached.

    You can enable this listener with `enablePositionReachedCallback()`.

    Note

    Since we can't get any feedback from the servo, this only works if the velocity (see `setVelocity()`) is set smaller or equal to the maximum velocity of the servo. Otherwise the servo will lag behind the control value and the listener will be triggered too early.

public class `BrickServo.VelocityReachedListener`()

  This listener can be added with the `addVelocityReachedListener()` function. An added listener can be removed with the `removeVelocityReachedListener()` function.

  public void `velocityReached`(short servoNum, short velocity)

    This listener is triggered when a velocity set by `setVelocity()` is reached. The parameters are the servo and the velocity that is reached.

    You can enable this listener with `enableVelocityReachedCallback()`.

    Note

    Since we can't get any feedback from the servo, this only works if the acceleration (see `setAcceleration()`) is set smaller or equal to the maximum acceleration of the servo. Otherwise the servo will lag behind the control value and the listener will be triggered too early.

### Constants

public static final int `BrickServo.DEVICE_IDENTIFIER`

  This constant is used to identify a Servo Brick.

  The `getIdentity()` function and the `EnumerateListener` listener of the IP Connection have a `deviceIdentifier` parameter to specify the Brick's or Bricklet's type.

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