1. RobotC Sensors

2. Learning Objectives Take a look at some of the options for VEX Sensors
Be able to configure sensors
Be able to use a touch sensor/limit switch to limit the movement of an arm
Be able to implement functions to help organize code
Be able to use the Ultrasonic Sensor to drive forward until you are near an object
Be able to use light sensors to track a line

3. Sensor Ports
UART (Universal Asynchronous Receiver/Transmitter) Ports 1, 2
Analog Ports 1-8
I2C
Inter-integrated Circuit Protocol
Allows several devices to be chained to one port.
Digital Ports 1-12
Speaker

4. Analog Sensors Light Sensor: 0 – 6 Feet
0 = Very Bright
255 = Dark
Line Tracker: LED Light + Light Sensor

5. Analog: Line Tracker Infrared light sensor and infrared LED.
Lights the surface and measures the light reflected.
Analog: 0 = Bright, Full Scale (4096 for Cortex, 1023 for PIC) = Dark
More Info at
Tracker-Instr-0312.pdf

6. Potentiometer: Analog
Measure the angle position
Measures 0 to 250 degrees +/- 20
Return values from 0 to 4096
Be careful, the sensor should not rotate beyond 250 degrees.

7. Analog Accelerometer
Measures acceleration non three axis simultaneously
Each channel being used connects to the controller (Cortex)

8. Digital: Limit Switch/ Bumper Switch
Can sense when arms reach their limit.

9. Digital Sensors Ultrasonic Uses two digital ports
Sensitivity: Detects a 3cm diameter pole at greater than 2m
Usable Range: 3.0 cm to 3.0 m / 1.5 in – 115 in

10. Digital Optical Shaft Encoder
Takes two digital ports
Can detect of to 1700 pulses per second = 18.9 rev/sec = rev/min

11. I2C Sensor Integrated motor encoders
Since it is I2C you can chain several (8?) encoders onto one I2C port.
cessories/sensors/encodermodules.html
Measures ticks per revolution when the motor is geared for torque.

12. We will use the Squarebot for Sensors Section

13. Configuring the Limit Switch
1) Select the Digital Sensors Tab
Robot -> Motors and Sensors Setup
3) Use the pull-down menu to select Touch.
2) Name the Sensor
frontLimit
4) Apply and OK.

14. Configuring the Potentiometer
Robot -> Motors and Sensors Setup
Select Analog Sensors tab
Using port 6
Name the variable: armPot
Select ‘Potentiometer’ from the drop down menu
Apply OK

15. Using the Limit Switch Can sense when arms reach their limit.
0 when not pressed
1 when pressed

16. Preventing the Arm From Lowering Too Far
Pseudo Code
If the down button is pressed AND the limit switch is not pressed
Go down
AND?
Remember the conjunctions?

17. Conjunctions Conditions can be combined using conjunctions && (AND)
while ((SensorValue[rightEncoder]<1800) && (SensorValue[leftEncoder] <1800))
{ //while both encoders are less than 1800 it will repeat the code in the {} block }
|| (OR)
while ((SensorValue[rightEncoder]<1800) || (SensorValue[leftEncoder] <1800))
{ // While either the leftEncoder<1800 or the rightEncoder is <1800 it will //repeat the code inside the {} block
! (NOT)
Turns true to false and false to true
while !(SensorValue(leftEncoder)>1800)

18. The && can only combine two complete conditions.
Putting it together
Pseudo Code
If the down button is pressed AND the limit switch is not pressed
Go down
The && can only combine two complete conditions.

19. Using the Potentiometer to Limit
Go to
And follow the video trainer lesson