Transcript Arduino Project Overview

Capacitance Sensor Project
Goal: Creation of a digital capacitance sensor circuit where a
variation in capacitance changes the frequency or period of
oscillation of a timer circuit. An Arduino Uno then measures
this change in the time period and displays an integer value
between 0 to 99 (base 10) to indicate the amount of
capacitance. A capacitance value of Cmin would be indicated
by a value of 0 and a value of Cmax would be indicated by a
value of 99. The current maximum value will be stored by the
sensor circuit and displayed on the serial monitor of a laptop
connected to an Arduino Uno.
ECE 3450
M. A. Jupina, VU, 2016
Capacitance Sensor Project
Sports Applications
Tank Application
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555 Timer
ECE 3450
M. A. Jupina, VU, 2016
Application of Your Capacitance Sensor
• Assume that you are designing an impact sensor for a
boxing glove where you want to capture only the
maximum impact of the glove on a boxing bag during a
training session.
• For a range of possible impacts, assume that no impact on
the capacitance sensor is a value of Cmin, whereas the
maximum possible impact on the capacitance sensor by a
boxer such as Mike Tyson would be a value of Cmax. The
display on the glove would indicate a value of 0 for no
impact and a value of 99 if Mike Tyson hit a boxing bag
with the glove.
• A reset button will also be available to clear the sensor so
that the maximum impact value can again be captured.
ECE 3450
M. A. Jupina, VU, 2016
Specifications of Your Capacitance Sensor
• Assume that the capacitance of the sensor varies as a linear
function of the impact applied to the boxing glove.
• The maximum capacitance that can be measured by the
sensor is
Cmax = 4 Cmin
• Therefore, the range of capacitance that is to be measured
is
DC = Cmax - Cmin = 3 Cmin
• When C=Cmin, the period of the timer circuit will be Tmin,
whereas when C=Cmax the period of the timer circuit is
Tmax since the period of the timer circuit increases as the
RC time constant time increases. The timer circuit will be
a 555 timer.
ECE 3450
M. A. Jupina, VU, 2016
Implementation of Your Capacitance Sensor
• Use the following Cmin values depending on your lab station #:
o Cmin = 0.001 mF, for lab stations 1, 4, 7, 10, 13, & 16
o Cmin = 0.01 mF, for lab stations 2, 5, 8, 11, 14, & 17
o Cmin = 0.1 mF, for lab stations 3, 6, 9, 12, 15, & 18
• To measure the period of oscillation of the timer circuit, use
pulseIn() in your Arduino sketch and a digital input pin to
measure the output signal of the timer circuit. Store only the
maximum value of the timer’s measured period of oscillation.
• Use one of the analog input pins to read in a voltage from a
voltage divider circuit that represents the offset value of Cmin.
Use a variable resistor (pot) in the voltage divider to get the
exact offset. The A/D converters on the Arduino are 10 bits so
the digital value varies from 0 to 1023 as the analog input
voltage varies from 0 to 5V (resolution is 5V/1023 or 4.89 mV).
The digital offset value is then used to “zero” the system output.
ECE 3450
M. A. Jupina, VU, 2016
Arduino Uno
ECE 3450
M. A. Jupina, VU, 2015
Block Diagram of the Capacitance Sensor
When C = Cmin, Output = 0
When C = Cmax, Output = 99
Reset
Serial
Monitor
on laptop
-
digital input
Max Period
Algorithm
f, T
ARDUINO
0 to 99
analog input
OFFSET Voltage
ECE 3450
M. A. Jupina, VU, 2016
Pre-Lab
Prelab Assignment
i. Go to https://www.arduino.cc/en/Main/Software to download the Arduino
software.
ii. Go to https://www.arduino.cc/en/Tutorial/BuiltInExamples for examples
of code for the Arduino.
iii. Provide a circuit diagram showing how your Arduino is to be connected to
the timer circuit and voltage divider. Show all details (pin numbers,
resistor values, etc.)
iv. Based on the background info in slide 5, write code to implement the
Arduino-based capacitance measurement system. After testing of the your
code, submit a print-out of your code.
ECE 3450
M. A. Jupina, VU, 2015
Lab Measurement Details
1)
2)
3)
ECE 3450
Repeat the measurements on the Arduino-based design.
Make a table showing the C value, T value, and the output
value shown on the display.
Demonstrate
through
calculations that the C, T, and the output values are correct. If
slight differences exist, what are the possible sources of error?
How do these measured values compare with the values
obtained from the DE2- based design.
Demonstrate that if the capacitance value is reduced, the
output display does not change (i.e., only the max value is
displayed). After pressing the reset button, does the display
now show a value consistent with the current capacitance
value?
M. A. Jupina, VU, 2016