Physical Computing

Physical computing

This section details the sensors employed by Mechamagnets, and code used to read the sensors.

Sensor List

Part Name	Part Number	Description	Source
Linear Hall effect sensor	A1324LUA-T	Package: 3-SIP Sensitivity : 5.0mV/G Suitable for sensing 1/8in by 1/8in N48 neodymium magnets at a distance of ~ 5 to 10mm.	Digikey
Linear Hall effect sensor	A1308KUA-1-T	Package: 3-SIP Sensitivity : 1.3mV/G Suitable for sensing 1/4in by 1/16in N48 neodymium magnets at a distance of ~ 5 to 10mm.	Digikey

Custom PCBs

🚧 Under construction 🚧

Arduino / Processing code

mechamagnet_instrumentation folder

mechamagnet_instrumentation.ino	Example Arduino sketch to read linear Hall effect sensors
in setup Serial.begin(9600);	Initialize the serial communication which we will use in Processing to obtain the sensor readings
in loop analogRead(analog_pin_number);	Read the sensor and return an integer based on the resolution of the ADC (10bit range = 0 - 1023). Linear Hall effect sensors return the middle value (512 in the case of 10bit ADCs) when it does not pick up any magnetic field. The values deviate from the middle according to the strength and polarity of the magnetic field.
in loop Serial.print(val); Serial.print(" ");	Print a sensor reading to the serial port, and then a space character. The space is use to separate each sensor value.
in loop Serial.println(); delay(25);	End the serial print with a line break. Processing will listen for this line break to determine when it has received a complete set of sensor readings. We inroduce a delay to avoid overloading Processing's buffer and to ensure minimal delay between sensor reading and visualization.

mechamagnet_instrumentation.pde	Example Processing visualization sketch
Objects MMButton MMKnob MMStick	Button: push buttons, switches etc. Knob: knobs, dials, rotary encoders etc. Stick: joystick, thumbsticks etc.
Creating an object	First, declare object, e.g. MMButton button Then, in setup, define object, e.g. button = new MMButton("BUTTON 1", 0, false, 0.5, 50, 50, 80, 200);
Updating and displaying object	in draw loop update object with serial data, e.g. button.update(SERIAL_DATA); then display object button.display();
Object arguments: MMButton MMButton(name, index, inverted, threshold, xpos, ypos, w, h)	name (String): object name, also used to name calibration CSV index (int): index of value from SERIAL_DATA to read inverted (boolean): TRUE—values decrease when button is pressed threshold (float): from 0-1, actuation point of button xpos, ypos, w, h (float): x position, y position, width and height of visualization.
Object arguments: MMKnob MMKnob(name, index0, index1, inverted, xpos, ypos, d)	name (String): object name, also used to name calibration CSV index0 (int): first index of value from SERIAL_DATA to read index1 (int): second index of value from SERIAL_DATA to read inverted (boolean): TRUE—flip first sensor reading xpos, ypos, d (float): x position, y position and diameter of visualization. if visualization rotates in the opposite direction, try switching index0 and index1.
Object arguments: MMStick MMStick(name, index0, index1, inverted0, inverted1, xpos, ypos, size)	name (String): object name, also used to name calibration CSV index0 (int): first index of value from SERIAL_DATA to read index1 (int): second index of value from SERIAL_DATA to read inverted0 (boolean): TRUE—flip first sensor reading inverted1 (boolean): TRUE—flip second sensor reading xpos, ypos, size (float): x position, y position and size of visualization. if visualization axes are swapped, switch index0 and index1.
Calibration method	Each object has its own calibration method(s). They can be accessed through the GUI button(s) under each individual visualizations. Calibrated values are stored in a CSV file located in the sketch's "data" folder, and named after the objects name field. When the sketch starts, it will attempt to find and load the object's calibration file; if the file cannot be found, a new file will be created.
MMButton fields	val (float array): an array with the last x number of sensor readings. val[0] (float): most recent sensor reading. min (float): minimum sensor value. max (float): maximum sensor value. threshold (float): button actuation point (0-1). threshold_val (float): button actuation point between min and max values.
MMKnob fields	val (PVector): an array of 2D vectors with the last x number of sensor readings. val[0] (PVector): Most recent sensor reading. val[i].x (float): first sensor reading. val[i].y (float): second sensor reading. angle (float): knob's angle of orientation. center_point (PVector): center of rotation. angle_offset (float): knob's start of rotation.
MMStick fields	val (PVector): an array of 2D vectors with the last x number of sensor readings. val[0] (PVector): Most recent sensor reading. val[i].x (float): first sensor reading. val[i].y (float): second sensor reading. start (PVector): minimum sensor readings. end (PVector): maximum sensor readings center_point (PVector): stick's center point.