Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc. Touch Sensor • This lesson will explain how to hook a standard micro switch into the Vex system to function as a custom digital 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
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Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc.
Touch Sensor
• This lesson will explain how to hook a standard micro switch into the Vex system to function as a custom digital 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.
Materials Needed
• Basic components– Limit switch– 3-wire cable (12") OR two
single wires– 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.
The Limit Switch as an Electrical Switch
• The Limit Switch either connects or disconnects two terminals electrically– The switch has 3 terminals,
but only uses two here– COM (sometimes marked
GND or ) establishes the electrical ground voltage
– The NO ("Normally Open") terminal is electrically disconnected from the COM terminal when the switch is open, and connected when the switch is closed
COMNO
Switch
COMNO
Switch
Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc.
Limit Switch as a Digital Sensor
• The voltage at the NO terminal can be used as a digital signal to determine whether the switch is closed or not– NO terminal voltage will
default to HIGH (+5V) if the switch is not closed
– Closing the switch changes the NO terminal voltage to LOW (0V = ground)
– HIGH is a digital 1,LOW is a digital 0
LOWHIGH
Switch
LOWLOW
Switch
Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc.
Solder Limit Switch Terminals
• Set LOW voltage:Black wire toCOM terminal
• Set output voltage: White wire toNO terminal
• NC terminal andRed wire are unused
Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc.
Crimp 3-Wire Connector
• 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– Red cable may be
omitted because it is not used
Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc.
Plug In to Micro Controller
• Plug the crimped connector into the Micro Controller – Analog/Digital port
bank in an Digital Sensor Port
– Port 5 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.
Load Online Code to Test
• Connect the micro controller to the PC and turn it on
• In easyC:– Build & Download menu– On-Line Window– Download On-Line Code
• Push the switch arm and watch “Digital Input 5” change
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