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 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 Concept Drawing Block Diagram

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?