VEX EDR Sensors

VEX EDR Sensors

Most VEX EDR sensors are compatible for use in the FIRST Tech Challenge! Use these to aid in autonomous mode and other programmed functions.

Note: To be compatible with FIRST Tech Challenge, VEX EDR sensors will need their connectors converted from male to female, or by using a female to female adapter.

Availability: In stock

OR
Product Name Availability Price Qty
Advanced Sensor Kit
275-1179

In Stock

$99.99
Analog Accelerometer V1.0
276-2332

In Stock

$39.99
Bumper Switch (2-pack)
276-2159

In Stock

$12.99
Light Sensor
276-2158

Out of Stock

$19.99
 
Limit Switch (2-pack)
276-2174

In Stock

$12.99
Line Tracker (3-pack)
276-2154

In Stock

$39.99
Optical Shaft Encoder (2-pack)
276-2156

Out of Stock

$19.99
 
Potentiometer (2-pack)
276-2216

In Stock

$12.99
Ultrasonic Range Finder
276-2155

Out of Stock

$29.99
 
Yaw Rate Gyroscope Sensor V1.0
276-2333

In Stock

$39.99

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Description

Details

The LIS344ALH capacitive micromachined accelerometer features signal conditioning, a 1-pole low pass filter, temperature compensation and g Select which allows for the selection among 2 sensitivities. Zero-g offset full scale span and filter cut-off are factory set and require no external devices.

The sensor will measure acceleration in both directions along each of the 3 axis. Acceleration along the X or Y axis in the direction of the silkscreened arrows will produce a larger reading, while acceleration in the opposite direction will produce a smaller reading. For the Z axis, upward acceleration (in the direction of the board's face) produces larger values, and downward acceleration (toward the board's back) produces lower values.

Gravity is indistinguishable from upward acceleration, so the sensor will detect a constant 1.0G while at rest. If the board is mounted horizontally, gravity will effect only the Z axis. If the sensor is tilted away from the horizontal, the gravity reading on the Z axis will diminish, and the readings on the other axis will change depending on which way you are tilting it.

Each channel used must be connected to an analog input on the VEX microcontroller using a standard servo extension cable. You don't have to hook up all the channels; you only need to connect the ones required for your application. The white (signal) wire of each extension cable goes near the 'X', 'Y', or 'Z' silkscreened on the board. The black (ground) wires go at the other end, adjacent to the 'B' silkscreened on the board. The center wire is for +5 volts. Also, the mounting holes are electrically isolated from the circuit.

The accelerometer has two sensitivity ranges, selected by a jumper. Pin 1 of the Jumper (the pin closest to the "Y" marking) connects directly to the LIS344ALH with a 1K pulldown resistor. Pin 2 of the Jumper connects to +3.3 volts. The easy way to remember the jumper settings is to add the values of the installed jumper; The larger the sum, the larger the range.

Jumpers

Sum

Range

Output (-1g to +1g)

none

0

+/- 2.0g

1.6 volts to 3.4 volts

1 only

1

+/- 6.0g

2.2 volts to 2.8 volts



You can control the Sensitivity Ranges remotely by connecting your control signal to pin 1 of the Jumpers. The Max Input voltage for the Jumpers is +3.3 Volts. For more details, please refer to the data sheet on the STMicroelectronics LIS344ALH chip.

  • Bumper Switch Sensor: The bumper sensor is a physical switch. It tells the robot whether the bumper on the front of the sensor is being pushed in or not.

  • Benefits:The bumper switch can help the robot avoid dangerous collision automatically.

  • Switch Info: SPST switch (“Single Pole, Single Throw”) configured for Normally Open behavior.

  • Switch Connection: Wired to normally open (OFF)

  • Signal Behavior: When the switch is not being pushed in, the sensor maintains a digital HIGH signal on its sensor port. This High signal is coming from the Microcontroller. When an external force (like a collision or being pressed up against a wall) pushes the switch in, it changes its signal to a digital LOW until the switch is released. An unpressed switch is indistinguishable from an open port.

  • Range Limits: Forces less than a pound can trigger the bumper switch (5.06 oz typical).


  • The bumper switch can allow a robot to navigate autonomously by avoiding hard collisions, such as hitting a wall. For example, a robot can be programmed to briefly freeze when the bumper switch is activated, and then reorient itself so that it is no longer driving towards the obstacle. Figure 2 shows where the bumper switch would be placed to be the first part of the robot to make contact with a wall or an obstacle.


    Figure 2. (a) Bumper switch placement; (b) Placement close-up

    The Light Sensor uses a photocell that allows your robot to detect and react to light. With the light sensor, you can program a whole new range of capabilities to your robot. A Programming Kit is needed to change the program in the VEX Controller.

  • Analog input of light levels
  • Usable range of 0 to 6 feet
  • Find dark or bright areas
  • Create more autonomous function
  • Limit Switch Sensor Signal: The limit switch sensor is a physical switch. It can tell the robot whether the sensor’s metal arm is being pushed down or not.

    Switch Type: SPDT microswitch, configured for SPST Normally Open behavior. Behavior: When the limit switch is not being pushed in, the sensor maintains a digital HIGH signal on its sensor port. This High signal is coming from the Microcontroller. When an external force (like a collision or being pressed up against a wall) pushes the switch in, it changes its signal to a digital LOW until the limit switch is released. An unpressed switch is indistinguishable from an open port.

    Benefits: Limit switches expand the functionality of robots by allowing controlled motion in moving components (e.g., gripper arm). They also allow the robot to better detect its surroundings, by detecting collisions with external objects.

    The limit switch is used to determine the proximity of equipment (the Applications section illustrates a few examples). The limit switch can output only two signals: ON and OFF. It outputs a digital ON signal when the lever arm is depressed and a digital signal OFF when the lever arm is not depressed (see Figure 2 below). External forces, such as collisions, produce a digital ON signal, which remains ON until the lever arm is released.



    Figure 2. (a) Limit switch OFF or not triggered; (b) Limit switch ON or triggered

    Limit switches provide the capability to limit action in programmed behaviors. For example, a robot can be programmed to stop forward motion if the switch is triggered ON. Figure 3 below shows a limit switch placed on the front of Squarebot. If this Squarebot were to run into a wall or another obstacle, the limit switch would be triggered ON and the robot would stop, as programmed.



    Figure 3. Squarebot with limit switch

    Similarly, triggering the limit switch can tell the microcontroller to stop rotating robot components, such as arms. A Programming Kit is needed to implement this (see Programming Resources for sample codes).



    Figure 4. Protobot utilizing a limit switch to stop a rotating arm

    Figure 5 shows a close-up of the limit switch placement on Protobot. As the limit switch runs into the horizontal bar below the lever arm, the limit switch is triggered ON and the microcontroller stops the arm from rotating.



    Figure 5. Protobot limit switch close-up

    The limit switch will be either in the ON or OFF state. The torque required to change from OFF to ON (i.e., depress the lever arm) for an unmodified limit switch is approximately 0.005N-m, which is equivalent to applying approximately 0.03lb 2in away from the lever arm pivot point. Figure 6 below shows the location of the pivot point. If the limit switch is modified this torque will vary. If necessary the specific torque or amount of force required to trigger the limit switch at a specific distance can be calculated using basic torque equations.



    Figure 6. Side view of limit switch showing lever arm pivot point

    A Line Tracker mostly consists of an infrared light sensor and an infrared LED. It functions by illuminating a surface with infrared light; the sensor then picks up the reflected infrared radiation and, based on its intensity, determines the reflectivity of the surface in question. Lightly colored surfaces will reflect more light than dark surfaces; therefore, lightly colored surfaces will appear brighter to the sensor. This allows the sensor to detect a dark line on a pale surface, or a pale line on a dark surface.

    The Line Tracker allows your robot to follow a pre-marked path and allows humans to indirectly control the robot while it is autonomous.
    The Line Tracker enables a robot to autonomously navigate a line-marked path. By drawing a line in front of a robot outfitted with a line tracker, one can dictate the robot’s patch by showing it where to go without using a remote controller. A typical application uses three line trackers, with the middle sensor aligned directly above the intended line.

    The range for the Line Tracker is approximately 0.02 to 0.25in (from the ground) with optimum sensitivity at 3 mm (about 1/8 inch). The minimum line width it can detect is 0.25in.

    The Line Tracker is an analog sensor, meaning that it can output many more values within its range of potential values (in this case, from 0-5V) than a digital sensor, which would output only a handful of discrete values in the range (e.g., 1, 2, 3, 4, and 5V), as is the case for a digital sensor. This range of output from 0-5V is sent to the microcontroller, which translates it into a corresponding range of integer values from 0 to full scale. Full scale is 1023 for 10-bit Analog-to-Digital values such as with easyC or ROBOTC for PIC, 4095 for 12-bit values such as with ROBOTC for Cortex and 255 for 8-bit values such as with MPLAB. When using the VEX ARM® Cortex®-based Microcontroller, typical white/black/"away from everything values" will be 38/662/770 for easyC, 153/2650/3076 for ROBOTC and 9/166/192 for 8-bit values. When using the PIC Microcontroller, typical white/black/"away from everything values" will be 38/882/1012 for both easyC and ROBOTC and 9/220/253 for 8-bit values.

    For this particular sensor, the output will be low when the surface is pale or highly reflective and high when the surface is dark and absorbs infrared energy.

    The Optical Shaft encoder is used to measure both relative position of and rotational distance traveled by a shaft. It works by shining light onto the edge of a disk outfitted with evenly spaced slits around the circumference. As the disk spins, light passes through the slits and is blocked by the opaque spaces between the slits. The encoder then detects how many slits have had light shine through, and in which direction the disk is spinning.

    Figure 1. Optical Shaft Encoder disk.


    The Optical Shaft Encoder can be used to improve a robot in various ways. The encoder can measure rotational distance traveled and speed, which can be used to monitor, for example, the angular position of a robot gripper arm or the speed of a robot. Knowing these parameters can greatly assist you with performing autonomous tasks with your robot.

    The Optical Shaft Encoder can be used to track distance traveled, direction of motion, or position of any rotary component, such as a gripper arm. The encoder can also be used to detect movement, which could facilitate richer interaction between the robot and its environment (e.g., human-robot interaction). If a human moves a robot arm that is attached to an encoder (e.g., during a handshake), the robot detects the arm movement and the direction(s) and distance(s) traveled, helping the robot classify the interaction as a handshake.

    Figure 2. Optical Shaft encoder mounting system

    While the diameter of the disk in the encoder does not really matter, the diameter of the wheel or gear whose shaft passes through the encoder does! The circumference of the wheel is equal to its diameter multiplied by pi (approx. 3.14). Multiplying the distance traveled which when multiplied by the number of revolutions gives of the distance traveled.

    Figure 3. Wheel circumference formula


    The optical shaft encoder can detect up to 1,700 pulses per second, which corresponds to 18.9 revolutions per second and 1,133 rpm (revolutions per minute). Faster revolutions will therefore not be interpreted exactly, potentially resulting in erroneous positional data being passed to the microcontroller.

    A potentiometer (or "pot") is an electrical device used to measure angular position. The user can therefore adjust the degree to which the potentiometer opposes electric current through it, simply by turning a shaft that is attached to the center of the potentiometer. As the resistance of the potentiometer changes, so does the voltage, which thus causes the potentiometer to act as a variable voltage divider. This varying voltage can be measured by the VEX microcontroller and is directly proportional to the angular position of the shaft connected to the center of the potentiometer. This allows you to obtain an analog measurement of an angular position. The VEX potentiometer is designed with a “D-hole” in the center, which should slide easily over the VEX square shafts. The potentiometer includes two arcs, each ½in from the center hole; these arcs exist to assist with mounting the potentiometer to the robot structure.

    Figure 1. Potentiometer graphic displaying how to use arcs for mounting.


    Note: Before you can use the potentiometer, you must reprogram your VEX microcontroller to read the varying voltage of the sensor on the corresponding port you are planning to connect to.

    Incorporating the VEX potentiometer kit into your project can make it easier for your robot to perform autonomous behaviors. A robot equipped with a potentiometer becomes aware of the position angles and motion of different components, thus making it more aware of its actions.

    The VEX potentiometer can be used to measure variations in angular position of different robot components. It can be very useful when implementing robot manipulators or shooters. For example, if you are designing a shooting robot, it is possible to estimate the angle at which the robot should shoot a ball in order to get the ball into the goal from a known distance.

    The mounting arcs allow for up 90º of adjustment to the potentiometer’s position. Since the potentiometer has limited angular travel, it is important to ensure that the shaft that is being measured by the potentiometer does not travel more than 260º (the potentiometer can only move approximately 265º ±5º and can only electrically measure 250º ±20º). The adjustment arcs allow the potentiometer’s range of motion to be repositioned to match the shaft’s range of motion.

    To measure the motion of something that rotates more than 230º, try gearing down the shaft’s motion such that the gear attached to this “primary” shaft turns a larger gear attached to a “secondary” shaft. This secondary shaft will therefore rotate less distance than the primary shaft. Once the gear sizes are adjusted such that the range of motion of the secondary shaft is within that of the potentiometer, attach the secondary shaft to the potentiometer. This way, you should be able to indirectly measure the rotation of the primary shaft by directly measuring the rotation of the secondary shaft.

    An ultrasonic range finder sensor enables a robot to detect obstacles in its path by utilizing the propagation of high-frequency sound waves. The sensor emits a 40kHz sound wave, which bounces off a reflective surface and returns to the sensor. Then, using the amount of time it takes for the wave to return to the sensor, the distance to the object can be computed. To increase the sensing range, the sensor can be mounted to a servo to allow it to rotate.

    Unlike the bumper switch and limit switch that alert you when they have been hit, the ultrasonic range finder sensor can alert you to an obstacle in the path of the robot prior to hitting it. This can allow you time to safely navigate around obstacles.

    The sensitivity of the sensor depends on the objects’ surfaces that are detected by the emitted sound waves. For example, a reflective surface may produce a different reading than a non-reflective surface. The resolution of the sensor also depends on the sound waves. However, sound waves can reflect or be absorbed and possibly not return with enough power.


    • Sensitivity: Detect a 3cm diameter pole at greater than 2m.
    • Usable Range: 3.0 centimeters - 3.0 meter / 1.5 inches - 115 inches
    • Frequency: 40 KHz
    • Resolution: 1 inch

    Connect the Yaw Rate Gyro to an analog input on the VEX Microcontroller using a standard servo extension cable. The black (ground) wire goes adjacent to the 'B' silkscreened on the board. The center wire is for +5 volts. The white wire is signal. The mounting holes are electrically isolated from the circuit.

    Kit Contents
    Advanced Sensor Ki (275-1179)

    The Advanced Sensor Kit contains (1) each of the following sensor kits:


    Line Tracking Kit (P/N: 276-2154)
  • (3) Line Following Sensors
  • (1) Inventor's Guide Insert

  • Ultrasonic Range Finder (P/N: 276-2155)
  • (1) Ultrasonic Range Finder Sensor
  • (2) 8-32 3/8" Screws
  • (2) Keps Nuts
  • (1) Inventor's Guide Insert

  • Light Sensor (P/N: 276-2158)
  • (1) Light Sensor
  • (2) 8-32 3/8" Screws
  • (2) Keps Nuts
  • (1) Inventor's Guide Insert

  • Optical Shaft Encoder (P/N: 276-2156)
  • (2) Optical Shaft Quadrature Encoders
  • (4) 8-32 3/8" Screws
  • (4) Keps Nuts
  • (1) Inventor's Guide Insert

  • Potentiometer (P/N: 276-2216)
  • (2) Potentiometers
  • (4) 1/2" Standoffs
  • (4) 8-32 1/4" Screws
  • (4) 8-32 1/2" Screws
  • (1) Inventor's Guide Insert


  • Analog Accelerometer V1.0 (276-2332)
  • (1) Accelerometer
  • (1) Jumper

  • Bumper Switch (2-Pack) (276-2159)
  • (2) Bumper Switches

  • Light Sensor (276-2158)
  • (1) Light Sensor

  • Limit Switch (2-Pack) (276-2174)
  • (2) Limit Switch Sensors

  • Line Tracker (276-2154)
  • (3) Line Tracker Sensors

  • Optical Shaft Encoder (2-Pack) (276-2156)
  • (2) Optical Shaft Quadrature Encoder

  • Potentiometer (2-Pack) (276-2216)
  • (2) Potentiometer

  • Ultrasonic Range Finder (276-2155)
  • (1) Ultrasonic Range Finder

  • Yaw Rate Gyroscope Sensor V1.0 (276-2333)
  • (1) Yaw Rate Gyroscope Sensor V1.0
  • Docs & Downloads
    CAD File
    Analog Accelerometer V1.0 (276-2332)
  • CAD File (STEP)
  • CAD Overview (PDF)

  • Bumper Switch (2-Pack) (276-2159)
  • CAD File (STEP)

  • Light Sensor (276-2158)
  • CAD File (STEP)

  • Line Tracker (276-2154)
  • CAD File (STEP)

  • Optical Shaft Encoder (2-Pack) (276-2156)
  • CAD File (STEP)

  • Potentiometer (2-Pack) (276-2216)
  • CAD File (STEP)

  • Ultrasonic Range Finder (276-2155)
  • CAD File (STEP)

  • Yaw Rate Gyroscope Sensor V1.0 (276-2333)
  • CAD File (STEP)
  • Inputs
    Analog Accelerometer V1.0 (276-2332)
    The sensor will measure acceleration in both directions along each axis.
  • Black: Ground
  • Red: +5V

  • Bumper Switch (2-Pack) (276-2159)
  • Type: Momentary

  • Limit Switch (2-Pack) (276-2174)
  • Trigger Force: 0.38oz oz typical (varies with location of applied torque on actuator)
  • Actuator Length: 2in

  • Line Tracker (276-2154)
  • Type - Light reflected from dark lines and a bright floor

  • Optical Shaft Encoder (2-Pack) (276-2156)
  • Type: Mechanical Rotation
  • Rotation: Continuous
  • Size: Standard VEX 1/8 in shaft

  • Potentiometer (2-Pack) (276-2216)
  • Type: Mechanical Rotation
  • Rotation: 250 degrees (measurable)
  • Size: Standard VEX 1/8 in shaft

  • Ultrasonic Range Finder (276-2155)
  • Start signal to the ultrasonic sensor. Connect to a interrupt port.
  • Outputs
    Analog Accelerometer V1.0 (276-2332)
  • 0.100 spaces pins (3 rows)
  • Connect to one analog input per axis (cables not included)
  • White: Output signal

  • Bumper Switch (2-Pack) (276-2159)
    3-Wire Cable
  • Black: Ground
  • Red: No Connect
  • White: Control signal

  • Limit Switch (2-Pack) (276-2174)
    3-Wire Cable
    Connect to a digital input
  • Black: Ground
  • Red: No Connect
  • White: Control signal

  • Line Tracker (276-2154)
    3-Wire Cable
    Connect to three analog inputs
  • Black: ground
  • Red: +5V
  • White: control signal
  • Optical Shaft Encoder (2-Pack) (276-2156)
    3-Wire Cable
    Connect to two interrupt inputs.
  • Black: Ground
  • Red: +5V
  • White: Control Signal

  • Potentiometer (2-Pack) (276-2216)
    3-Wire Cable.
    Connect to an analog input.
  • Black: Ground
  • Red: +5V
  • White: Control Signal

  • Ultrasonic Range Finder (276-2155)
    3-Wire Cable Connects to a interrupt port. Echo response from the ultrasonic sensor.
  • Black: Ground
  • Red: +5V
  • Orange/Yellow: Control Signal

  • Yaw Rate Gyroscope Sensor V1.0 (276-2333)
  • Measures rotational rate in degrees per second (dps) and outputs a proportional analog value.
  • Size
    Limit Switch (2-Pack) (276-2174)
  • Actuator Length: 2.0in total
  • Unit Dimensions: 1.26in L x 1.21in W x 0.5in H

  • Potentiometer (2-Pack) (276-2216)
  • 1.75" x 1.5"
  • Compatibility
  • All sensors compatible with 3-Wire Extension Cables