While most 3D printers employ a limit switch on each axis, some designs call for a Z-probe in place of or in addition to a Z-axis limit switch. Very rarely is this type of limit switch used to home carriages. Similar to the mechanical limit switch, the carriage has to touch the force-sensitive resistor for it to be detected. This intermediary controller board relays a logic level signal to the printer motherboard. With these types of switches an extra controller board is required to measure the changes in resistance of the FSR. Force-Sensitive Resistors (FSR), as their name implies, change resistance when experiencing force. The final type of limit switches is resistive. Unlike an optical sensor, the Hall sensor is not affected by ambient light. Similar to the optical sensor the Hall sensor needs an extra wire but in this case itвЂ™s for a reference voltage required for the switching effect. As the carriage moves the magent closer to the minimum and hence the magnetic sensor there will be a distance at which an output signal is triggered. These types of switches require a magnet to be attached to the carriage. Similar to the optical limit switch Hall based switches are contactless, but instead of detecting changes in light they measure changes in magnetic fields. Magnetic limit switches operate on either the principle of electromagnetic induction or the Hall effect. However, interference from ambient light is a slight concern. You donвЂ™t have to worry about parts fatiguing or wearing out overtime like the spring arm of the mechanical switch.

With optical limit switches the detection of the carriage is a contactless process. However, unlike the mechanical switch the optical switch requires an extra wire that supplies power for the LED. Most optical switches output a digital high or low signal based on if an obstruction is present, making this limit switch type compatible with many 3D printer motherboards. When the light path between the LED and phototransistor is blocked the base current of the phototransistor decreases. Optical limit switches consists of an LED and phototransistor. When placed on a linear rail the carriage will bump into the limit switch and the microcontroller will sense a change in the state of the switch and will stop stepping the motor.

When pressed the switch will either open or close a circuit, depending on how it is wired. It is fundamentally a push button that is triggered when its metal spring arm is bumbed. The mechanical limit switch is the most commonly used because of its simplicity and low cost.

At the top of your screen, click on вЂSketch,вЂ™ then вЂInclude Library,вЂ™ then вЂAdd.

Ultrasonic Test: test the ultrasonic sensor by telling the robot to move forward until it is 5cm away from an obstacle.

Touch Test: tests the touch sensor/limit switch to display whether or not the button/switch is pressed.

IR Obstacle Test: tests the IR obstacle avoidance sensor.

Gyro Turning Test: tells the robot to do a 90o left and right turn based on the gyro sensor.

Gyro Library Test: tests the gyro sensor to display the x,y, and z Euler angles.

Movement Test: tests the standard robot movements, such as forward, turns, and claw movement.

These Arduino C codes provided show the possibilities of the robot and provide tests for different functions.

Ultrasonic: reads the distance from itself to the nearest object it sensesД®xample files can be found by clicking on File>Examples>Vex.

Gyro: reads data from the MPU6050 and provides the Euler angles around 3 axises.

There are 2 classes that control different sensors:

Vex: commands the motor shield, and controls the motors for all robot movement.

There is one main class that controls the robot: This library relies on multiple 3rd party libraries, including MPU6050, I2Cdev, and Adafruit Motor Shield V2, as well as inbuilt Arduino libraries including Wire.

Control two motors speed and direction simultaneouslyДownload the library files here Library Structure.

Control single motor speed and direction.

The library also allows for the following functions of the motor board:

VEX Touch/Button and VEX Limit Switch Sensor.

MPU6050 Accelerometer and Gyroscope Sensor.

The library allows you to interface with the following sensors:

The library is intended for use with the Adafruit Motor Shield V2, and VEX EDR 2-wire motors. For more information on coding with Arduino, please reference the Arduino Coding Guide The library is designed to more easily access the robotвЂ™s functionality. The VEX library is used in the EG1003 course to control the VEX robot and sensors using Arduino. 1.3 Alternative Way to Import the Library.

Vex limit switch sensor