Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc. CAN I MAKE MY OWN SENSOR 2 This lesson will explain how to hook a standard dial potentiometer into the Vex system to function as a custom analog sensor. Vex offers a limited selection of sensors that are optimized to work with the system. Don’t let this limit your creativity. Off-the-shelf sensors and electrical components can be adapted to work with the Vex system. Adapting off-the-shelf components is different in every case; you should take all the necessary precautions and be sure to understand the electrical behavior and requirements of each device before attempting to use it.

Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc. CAN I MAKE MY OWN SENSOR 2 Basic components Potentiometer 3-wire cable (12") Wire stripper Soldering Soldering pen Solder Vice Crimping Male Molex pins (3) Molex connector (1) Crimping tool

Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc. CAN I MAKE MY OWN SENSOR 2 The potentiometer is a resistor with an adjustable resistance (via dial) The potentiometer has 3 terminals The two outside terminals define the maximum and minimum voltages that the potentiometer can read The voltage of the middle terminal will have a voltage that is determined by the position of the knob on top. Minimum Voltage Maximum Voltage Voltage set by knob

Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc. CAN I MAKE MY OWN SENSOR 2 The variable voltage on the middle terminal can act as the sensor output for the potentiometer "dial sensor" A low voltage will register a high numeric reading in ROBOTC in the Vex micro controller A high voltage will register a low numeric reading in ROBOTC 0V +5V Output voltage

Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc. CAN I MAKE MY OWN SENSOR 2 Set min voltage: Black wire to First terminal Set output voltage: White wire to Middle terminal Set max voltage: Red wire to Third terminal Note: Picture is shown from rear so wire order appears reversed

Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc. CAN I MAKE MY OWN SENSOR 2 This end of the cable will be plugged into the Micro Controller Create a standard 3-pin Molex connector Wire order must be Black-Red- White

Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc. CAN I MAKE MY OWN SENSOR 2 Plug the crimped connector into the Micro Controller Analog/Digital port bank in an Analog Sensor Port Port 1 is set this way by default Black wire must go on the same side as black wire on regular Vex connectors

Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc. CAN I MAKE MY OWN SENSOR 2 RE-DOWNLOAD FIRMWARE (IF NECESSARY) You may have to re-download the RobotC firmware if you have ever downloaded any programs or other firmware to the microcontroller. (If nothing has been downloaded to the microcontroller after downloading the ROBOTC firmware, you may skip this step.) Connect the programming module to both the PC and the microcontroller Make sure the microcontroller is turned on Open ROBOTC. Select Robot/Download Firmware Select VEX VM 0724.hex/Open (or later version of ROBOTC firmware).

Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc. CAN I MAKE MY OWN SENSOR 2 Click Robot/Debugger. A Devices window should appear. Under Sensors, next to in1/Raw Value, there should be a number between Test the sensor. Observe the value for in 1 Turn the dial on the potentiometer and observe how the sensor value on in1 changes