Remote Control

The commutator communicates with a computer using JavaScript Object Notation (JSON) strings sent over the USB cable using a (virtual) serial port connection. This allows it to be controlled from any piece of software or script capable of writing data to a serial port. Virtually every programming language will have a library for doing this (e.g. the pySerial Python library). Additionally, many pieces of software (e.g. Bonsai, Labview, Arduino IDE) provide the ability to write to a serial port without any programming.

Note

An easy way to test remote control of the commutator is to to type commands into the Arduino IDE’s serial monitor.

Attention

Manual control takes precedence over remote commands. The commutator will dispose all JSON commands that a received while manual controls are in use.

JSON Commands

JSON is a human-readable data interchange format used to specify a property and assign a value to or read the value of that corresponding property. The notation is:

{property: value}

The commutator responds to six JSON properties: enable, led, speed, accel, turn, and print. The set of acceptable values depends on the property to which the value is being assigned. Each of these properties is documented here:

{enable: bool}

A boolean value to enable or disable the commutator.

• true: enable the commutator.

• false (default): disable the commutator

For example, to enable the commutator:

{enable: true}

{led: bool}

A boolean value to enable or disable the status LED.

• true (default): Turn on the status LED

• false: Turn off the status LED.

For example, to turn the status LED off:

{led: false}

{speed: float}

A floating point value in the range (0, 1000] to set the maximum rotation speed in RPM. The default value is 100 RPM. For example, to set the maximal rotation speed to 6.28319 RPM:

{speed: 6.28319}

{accel: float}

A floating point value in the range (0, 1000] to set the maximum rotational acceleration in RPMM. The default value is 200 RPMM. For example, to set the rotational acceleration to 6.28319 RPMM:

{accel: 6.28319}

{turn: float}

A floating point value indicating the number of turns to perform. The sign indicates the direction of motion. Turn commands are integrated. For instance, if a second turn command is received before the first completes, the final position of the commutator will be the sum of both commands. For example, to turn the commutator clockwise (from some perspective) 1.1 turns:

{turn: 1.1}

To turn it back counterclockwise (from the same perspective) by 0.5 turns:

{turn: -0.5}

{print:}

Return a JSON string containing parameters and motor operational state. For example:

{print:}

might return

{"led": false, "enable": true, "speed": 6.28319, "accel":6.28319, "target":-42.00, "motor_running": true}

where “target” is the target position of the motor in rotations and “motor_running” indicates if the motor is currently turning.

Compound JSON commands

Multiple commands can be sent in a compound JSON message in the following format:

{property1: value1, property2: value2, property3: value3}

The order of properties does not matter. For instance:

{led: false, speed: 25, turn : -1.1}

will turn the LED off, set the maximum speed to 25 RPM, and tell the commutator to turn 1.1 rotations CCW, but the order that these events happen in hardware is dictated by the firmware.