ECE 477 Design Review: Team 2 Fall 2010

ECE 477 Design Review:Team 2 Fall 2010

Andrew Phillips, Ben Laskowski, Shannon Abrell, Rob Swanson

Outline Project overview Project-specific success criteria Block diagram Component selection rationale Packaging design Schematic and theory of operation PCB layout Software design/development status Project completion timeline Questions / discussion

Project Overview

eV-TEK, or Telemetry for Electric Karts, is a tool for collecting and transmitting electric go-kart parameters in a race situation.

The collected data can help the driver and pit crew optimize vehicle performance and ultimately win races.

Project-Specific Success Criteria An ability to report the approximate

number of laps remaining on a given battery charge

An ability to detect and report cell voltage anomalies

An ability to sense and display kart speed

An ability to track the number of laps completed

An ability to log and display vehicle telemetry data

Block Diagram

Component Selection Rationale Op-Amps – LM324

Operates from single 5v supply Low supply currents (700μA per amplifier) Low cost

Current sense amp – INA148 Inputs need not be referenced to circuit ground Large common-mode input voltage range

External ADC – MCP3204 Needed extra ADC channels This IC inexpensive and meets speed/resolution

needs

Component Selection Rationale, cont’d Battery Management Micro –

PIC18F4423 13 ADC channels w/ 12-bit resolution Easily obtained Mature technology (few silicon errata items)

Main Micro – PIC32MX575F256L 6 UARTs, product familiarity

Wireless – XBee Pro 900MHz 6 mile range, sufficient data transfer speed

Packaging Design

Main Packaging Aluminum Aerodynamic Sits in front of

driver on roll cage Detachable

faceplate holds main board

Driver displays Wiring connection

at rear

Packaging Design

Battery Management Stand-alone

package Plastic case

provides electric isolation

Slots for battery leads and serial line to main controller

Schematic/Theory of Operation Voltage Follower

Acts to increase input impedance of ADC channels

Allows the use of large divider resistor values for low current drain

Schematic/Theory of Operation Battery Micro

Digitizes and scales battery voltages via simple code

Integrates current flow over time to obtain battery charge

Schematic/Theory of Operation External ADC

Used to increase number of ADC channels available

Interfaces to battery microcontroller over SPI

Schematic/Theory of Operation Main

microc0ntroller Can run up to

80MHz = 80MIPS Collects and

processes data from battery packs and sensors; logs; transmits to pit area

Schematic/Theory of Operation Power supply

Converts 12V to 5V and 3.3V

High-efficiency switchmode regulator for 12->5V conversion

Linear LDO for 5->3.3V

Maximum power dissipation ~2.4W

Large copper pours on PCB for heatsinking

Schematic/Theory of Operation Optical isolation

Battery monitors float with respect to main control board

1kV of isolation provided; we require ~50V of isolation

Servo motors also isolated “just in case”

Side benefit: 3.3V<->5V conversion

Schematic/Theory of Operation XBee module

Appears as serial port to PIC32

Hardware flow control pins used to minimize risk of buffer overflow

Schematic/Theory of Operation LED Drivers

TLC5917 Similar to 74HC595

but includes constant-current output drivers

Ease PCB routing – 3 wire bus instead of 13

Schematic/Theory of Operation USB-Serial

converter Makes USB appear

as UART for PIC32 Eases software, PCB

layout Mature product,

most errata fixed by manufacturer

Schematic/Theory of Operation DataFlash IC

2MB EEPROM-like device for data logging

Simple SPI interface; faster and more versatile than SD card

Data made available for download via USB interface

PCB Layout – Battery Monitors Voltage followers

Mostly uninterrupted ground plane for noise rejection

Decoupling capacitor very close to op-amps – vital for stability

PCB Layout – Battery Monitors Current monitor

Completely uninterrupted ground plane

Voltage reference IC and decoupling caps very close to op-amp

PCB Layout – Battery Monitors Digital

components Separated from

analog components As many extra

micro pins as practical padded out

Decoupling capacitors as close as practical to each power pin

PCB Layout – Battery Monitors Power supply

Linear LDO regulator

Expected power dissipation ~100mW

Bulk capacitor located nearby for stability

PCB Layout – Main Board

Microcontroller Decoupling

capacitors located physically and electrically close to chip

Every pin is padded out for debugging and/or expansion

Pads provided for precision oscillator module, though it should not be required

PCB Layout – Main Board

Power supply Switching regulator

is on top of continuous ground plane, and high dI/dt nodes are very short

Linear regulator has many vias to copper plane for heatsinking

Sufficient capacitance nearby for low ripple

PCB Layout – Main Board

Optical Isolation Physically separate

from most other critical interfaces

Keepout areas near battery connectors – physical isolation is several times what is required

PCB Layout – Main Board

Xbee Antenna connection

is as far from other components as possible

Capacitor located nearby to provide current pulses during RX->TX mode switches

PCB Layout – Main Board

LED Drivers Located directly

underneath 7-segment LED modules for compactness

PCB Layout – Main Board

USB UART Trace length from

USB connector is minimized to preserve differential nature of bus

Decoupling capacitors located as close as possible

PCB Layout – Main Board

EEPROM Located under

PIC32 for layout convenience and to minimize length of high-speed SPI traces

Decoupling capacitor nearby

Software Design/Development Status Battery monitors

Software is essentially done Need mechanism to calibrate

measurements▪ Preliminary tests indicate this will be easy

Roughly 400 lines of well-commented assembly code

Software Design/Development Status Main controller

Began reading up on various microcontroller features (DMA, interrupt mechanism)

Installed and began experimenting with C compiler

Simple programs compile successfully

Project Completion TimelineItem Expected Completion WeekOrder all remaining components 8Complete design and order main PCB

9

Complete battery monitor software 10Assembly of battery monitor boards 10Complete battery monitor packaging 11Main board software complete 13Assembly of main board 13Complete main package enclosure 14Final integration 15

Questions / Discussion