Transcript Slide 1 - ECpE Senior Design

Electronic Automobile Fluid Level Sensor
Team Members
 Team
 Nick Johnston, Team Leader
 Alex Garr, Communications Coordinator
 Drew Combs
 Dan Dillon
 Client
 Chris Justice
 Faculty Advisor
 Dr. Jiming Song
Planning
 Problem Statement
 The current method for measuring engine oil level is
messy, time consuming, and inconvenient.
 Market survey
 No simple replacement for the conventional dipstick
exists.
 Several measurement methods were considered.
 Capacitive sensor is small, cheap.
System
Block Diagram
Concept Drawing
 System description
 Sensor sends reading to measurement circuit
 Measurement circuit sends signal to microcontroller
 Microprocessor determines oil level, displays reading
 User interface tells microcontroller when to read data
 Calibration gets input from user, reads data from sensor,
and stores settings in microcontroller
Functional Requirements
 Pressing the “measure” button shall return a reading
within 3 seconds
 The device shall correctly measure whether the oil is
below, within, or above acceptable limits
 The proper LED shall remain lit for 15 seconds
 The devices shall provide over 300 oil checks on one
battery.
Non-Functional Requirements
 Sensor components immersed in oil shall withstand
220° F
 Device shall not require any external power source
 Device shall work regardless of orientation
 Sensor shall not degrade or introduce harmful
substances into the engine
 User shall be able to drop in the device in place of
current dipstick with no modification to vehicle
 All currents within the device shall not exceed 50 mA
 All voltages within the device shall not exceed 3 V
Project Plan
 Microsoft Project used to generate work breakdown
 Deliverables
 Proof-of-concept prototypes
 Sensor schematics, PCB layouts
 Software design documents
 Risks involved
Block Diagram
Design Method
- Capacitive Sensor
- A sensor which is placed on the end of a dip stick to measure the level
of oil through by seeing how much capacitance the sensor outputs.
- Capacitance Measuring Circuit
- This circuit uses a 555 timer which is dependent on a sole capacitive
value to create a square wave output. The square wave’s frequency is
dependent on the capacitive value and preset resistor values.
- Microcontroller
- The microcontroller then is able to count the pulses in the square wave
to determine it’s frequency and the level of oil. The microcontroller
will then output the corresponding value to the user interface.
Software Specification
UI Specifications
3 LEDs – Red, Yellow, Green
2 Button – Measurment, Hard Reset
red: need >= 1 quart
yellow : need ~ ½ quart
green : good
red flash : too much oil
green/yellow flash : measuring
All LEDs flashing : calibrating
measurement button : press to take a measurement, hold to calibrate
hard reset button : press to reset entire system, possible transient
hardware/software faults
Testing Specification
 Software
 white box
 black box
 code analysis
 Hardware
 component
 system
 Integration
 black box
 microwave
 heat
Circuit Diagram
This is the overall circuit
which can be separated
and examined in 3
different blocks: The
microcontroller, the
capacitance measuring
circuit, and the capacitive
sensor
Capacitance Measuring Circuit
The circuit diagram to the
left is the capacitance
measuring circuit. This
circuit uses a 555 timer to
create a square wave which
is dependent on the
capacitance of C4. C4 will
be the capacitance gathered
from the capacitance sensor.
In this way we are able to tell
the change in capacitance
by relating it to the change in
frequency of the output.
Sensor Layout
• Cadence Layout Plus used for design drafting.
• Narrowest possible traces (6 mil) to maximize capacitance
surface area and resolution.
• Use of both sides of the board so traces can be as wide as
possible.
• Differential design so that outside influences will have
minimal effects on reading.
Sensor Principles
• Measures Capacitance of the area surrounding the sensor.
• Fringe effect capacitance is the primary amount of
capacitance measured.
• As an object with a higher dielectric constant approaches the
sensor, the total capacitance of the circuit increases.
• Minimal distances between traces lead to greater effects on
capacitance due to the oil surrounding the sensor.
Sensor Application
• The sensor is attached the end of an OEM equivalent
•
•
•
•
dipstick and is submersed in the oil of the automobile
engine.
There are five capacitive circuits on the board.
Each circuit will be polled numerous times by the
microcontroller to gain an average capacitance per circuit.
Finding the greatest difference in capacitance between two
adjacent circuits determines where the oil level is.
The differential design allows for repeatable and accurate
results despite changes in oil temperature, oil quality, and
the external environment.
Software Design (1/2)
Powerup:
void Init():Sets the power mode to the higher power, operational
state.
Powerdown:
void Shutdown():Sets the power mode to the lowest power state.
Calibration:
void mainCal(): Main calibration routine
void setCalData(char data, char stage): Saves the calibration data
into nonvolatile memory
void blockInterrupt(): Wait until the pushbutton interrupt arrives
Software Design (2/2)
Measurement:
void mainMeasure(): Main measurement routine
char interpolate( char data ): The returned value is the relative oil
level based off interpolated calculations
UIControl:
char buttonPressed(): Determines whether or not the button is
pressed.
void LEDController( char active, char blink): Two LED mapped
characters are set to either activate or blink LEDs.
SensorInterface:
char pollSensor(): Sets the lines to poll the sensor and return the
raw data
Microcontroller
 TI-MSP 430 chipset
 Suggested by customer
 Chosen Model MSP430FF1101A
 Needed small amount of flash memory
 1KB program memory
 128B flash memory
 128B ram
 Two I/O, 8-bit and 6-bit buses
The CR2032 Battery
•One 3 Volt battery gives significant voltage and
power for use in our embedded system.
•A Lithium battery
•Chosen for it’s small and slim like size
Summary Of Work
 Nick Johnston – 76.5
 Dan Dillon – 76
 Drew Combs – 63
 Alex Garr – 68
 Created engineering project plan and design
 Started implementation of hardware and software
designs
Questions?