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ECE 477
Digital Systems Senior Design Project
Rev 9/12
Homework 5: Theory of Operation and Hardware Design Narrative
Team Code Name: Hackers of Catron Group No. 03
Team Member Completing This Homework: Joshua Hunsberger
E-mail Address of Team Member: jhunsber@ purdue.edu
NOTE: This is the second in a series of four “design component” homework assignments,
each of which is to be completed by one team member. The body of the report should be 3-5
pages, not including this cover page, references, attachments or appendices.
Evaluation:
SEC
DESCRIPTION
MAX
1.0
Introduction
5
2.0
Theory of Operation
20
3.0
Hardware Design Narrative
20
4.0
Summary
5
5.0
List of References
10
App A
System Block Diagram
10
App B
Schematic
30
TOTAL
100
Comments:
SCORE
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1.0 Introduction
Hackers of Catron is an electronically enhanced version of the popular Settlers of Catan
board game. Game setup will be automated, placement of physical pieces on the board will be
tracked, and resource trading will be handled through handheld devices. These enhancements to
the game will make the game easier to set up and play, resulting in a much improved game play
experience.
The display of board setup requires that each hexagon (hex) be recognizable as one of the
five resource types or the desert and must be associated with a rarity that corresponds to a
possible sum of two thrown dice. In order to accomplish this, the design utilizes a combination of
RGB LEDs to designate resource types and two-digit seven-segment displays to designate the
rarities. In order to sense the position of all the pieces the design uses a grid of Hall Effect
sensors which indicate when a magnet has been placed above them.
2.0 Theory of Operation
The Hackers of Catron circuit comprises three major functional subsections: The Hall Effect
sensor array, the RGB LED array, and the seven-segment display array. In addition there are
several minor functional subsections including the power supply, the Raspberry Pi interface, and
an additional Hall Effect sensor which did not fit in the array. Across all subsections, all ICs are
powered by the 3.3V supply rail, chosen primarily to eliminate the need for voltage level
translation since the Hall Effect sensors and microcontroller (MCU) both operate at 3.3V [1][2].
The operating mode and conditions for each functional block are summarized at the end of this
section.
The purpose of the Hall Effect sensor array is to sense the presence and position of pieces
placed on the playing surface. The presence of a piece is indicated by the output of a Hall Effect
sensor. The position of the piece can be determined by correlating each sensor to a physical
position (implemented in MCU code). To save pins, sensors are grouped into 18 “columns” of 8
“rows” each. The MCU can access any row of 18 sensors by outputting the correct address on 3
select pins of discrete multiplexers into which each column is fed.
The RGB LED array is designed to represent a hex’s resource type with unique,
distinguishable colors. The array will also be used as feedback during game play to indicate
improper piece placement or piece placement confirmation as needed. In order to control the
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color and brightness of the RGBs, the MCU sends commands via a two-wire interface to 7 ninechannel LED driver chips. The driver chips can communicate at up to 5MHz [3], so there should
be no issues with updating the state of the RGBs quickly. The driver chips also have their own
data line buffers, echoing the data and clock lines on a pair of output pins, so the chips will be
daisy-chained together. The LED control outputs are open-drain, which allows the LEDs
themselves to be powered by the 5V rail. This is done because the green and blue LEDs have
typical forward voltages of 3.2V and up to 4.0V [4], making it unfeasible to drive them with the
3.3V rail. Furthermore, each channel will control two LED’s in parallel in order to increase light
coverage on each hex.
The seven-segment display array is used to represent the relative rarity of each hex. Since
the possible value for each hex can go up to 12, two digits are required for each hex, making a
total of 38 digits. To control all these seven-segment displays, the MCU uses SPI to shift control
data to 5 eight-digit control chips. Each chip requires a load-enable or slave-select line to be
driven low in order to accept control data, but will also shift out control data as long as the loadenable line is not driven high again[5]. This allows the MCU to shift data into all 5 chips at once
while only using one load-enable line. The chips are connected to both the anode and cathodes of
each digit, and only a single resistor is required to set the current for each segment.
In order for players of Hackers of Catron to user their mobile devices to play the game, a
Raspberry Pi acts as a server and a wireless access point. To retrieve the status of the game and
communicate the state of the economy back to the MCU, several data lines must be used. I2C is
supported by both the MCU [1] and the Raspberry Pi, so only two lines are required to connect
the two devices. However, because the Raspberry Pi already has a 26 pin header, for simplicity
the PCB will also feature a 26 pin header, to which any pins not assigned tasks will be routed.
The Raspberry Pi is powered by 5V unregulated and uses a USB interface to get this power.
The board requires two voltage rails. The RGB LEDs and the Raspberry Pi are powered by
5V unregulated, while everything else is powered by 3.3V regulated power. Therefore, a simple
5V AC adaptor is used to draw power from a typical AC outlet. This is then regulated down to
3.3V to power the more sensitive ICs on the board. In order to protect the rest of the board
during construction and testing, several jumpers are used to isolate the power supply and the
regulator from everything else.
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Table 1 Operating Mode Summary
Subsection
Component
Function
Operation
Sensor
Hall Effect sensor
Detect piece
3.3V, active low, open
drain, .47uF bypass cap,
15kΩ Pull up resistor
Multiplexer
RGB
RGB LED
Organize sensors, reduce pin
3.3V, complemented output,
count
3 SEL lines, 8:1
Distinguish hex resources
5V, 15-20mA, parallel,
common anode
9CH LED driver
Control RGB color
3.3V, open drain,
Input: 1 data, 1 clock line
Output: 1 data, 1 clock
7Segment
2digit 7seg display
Display resource rarity
3.3V, 20mA/segment
8digit driver
Control 7seg display
3.3V, 160mA/digit, SPI
Input: 1 data line, 1 loadenable, 1 clock
Output: 1 data line
3.0 Hardware Design Narrative
To communicate and coordinate all the major subsections of the circuit, the MCU utilizes
the SPI, I2C, and general purpose subsystems. Port selection was done on a restrictive-first basis,
so that subsystems with the least flexibility in pin selection were assigned pins first.
I2C is used to communicate with the Raspberry Pi. The I2C subsystem is a part of the
MCU’s Two Wire Interface (TWI) subsystem. Since the TWI interface only has one choice for
its pin, it was given a pin assignment first. SPI, used to communicate with the seven-segment
display array, was the next most restrictive subsystem. This pin assignment was made so that all
four pins used are physically close to each other (see Appendix B), which should simplify
routing.
To drive the select line of all 18 multiplexers present in the sensor array subsection, three
of the MCU’s four high-drive pins were chosen as address lines. Although the 1mA driving
capability of any GPIO pin should be sufficient, having the capability to drive 4mA on the high-
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drive pins may prove beneficial in the future. The 18 return lines from the multiplexers along
with the output of the solitary Hall Effect sensor are assigned to the remaining pins on Port A.
Finally, the two pins used to communicate with the nine-channel LED drivers were assigned to
two pins next to each other on Port B.
There were several pins unavailable for assignment, including PortA pins 0-2 for JTAG
programming requirements. Any pin left unassigned will be routed to a header pin for debug or
communication with the Raspberry Pi. Furthermore, all communication signals are routed to the
header pin for debugging during fabrication.
The MCU can be powered with single or dual power supplies. All IO pins and the analog
subsection are powered by 3.3V, while the core and PLL are powered by 1.8V. We decided to
utilize the MCU’s internal voltage regulator to supply the 1.8V from the 3.3V rail. For this to
work 3.3V must be attached to the VDDIN pin and the VDDOUT pin must be routed to the
VDDCORE and VDDPLL pins. In order to avoid supply rail ripples, bypass capacitors are
required on both the 3.3V and 1.8V lines. Because our design does not utilize any analog
functions, the ADVREF pin is tied to ground in order to save power, as recommended by the
MCU’s datasheet.
Table 2 Port Assignment
Ports
Subsystem
Function
PA09, 10
TWI
Raspberry Pi communication
PA14...16, 28
SPI
Control 7seg display
PA20...22
GPIO
Select address lines for sensor array
PA03...08, 11...13, 17...19, 23...27, 30, 31 GPIO
Sensor array return lines
PB10, 11
GPIO
Control RGB display
RESET_N, VDDIO, TCK, PA00...02
On-Chip Debug
Programming via JTAG interface
4.0 Summary
The Hackers of Catron circuit must accomplish 4 basic tasks: sense pieces, display a
playing board, facilitate trading, and provide enough power to accomplish the first three tasks.
The first two tasks are accomplished via arrays of sensors and LEDs controlled by a string of
drivers. The third task requires a communication protocol between the Raspberry Pi and the
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MCU which is fulfilled with I2C. All power will be provided by a 5V unregulated supply
regulated down to 3.3V for the CMOS devices.
The MCU interface is primarily concerned with serial communication to other devices.
The only exception is the sensor array, which uses 3 address lines to select the row of 18 sensors
the MCU will read.
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5.0 List of References
[1]
Atmel, “32-bit ATMEL AVR Microcontroller,” 3 2012 [Online]. Available:
http://www.atmel.com/Images/doc32059.pdf. [Accessed 13 2 2013].
[2]
Toshiba, “TCS20DLR,” 2 2011. [Online]. Available:
http://www.semicon.toshiba.co.jp/info/docget.jsp?type=datasheet&lang=en&pid=TCS20
DLR. [Accessed 13 2 2013]
Omron, "LED Control IC W2RF004RM," 8 2012. [Online]. Available:
http://components.omron.com/components/web/pdflib.nsf/0/A59093552C8ED1C186257
A5D0077B1D2/$file/W2RV004RM_0812.pdf. [Accessed 13 2 2013].
AMS, "AS1116 LED Driver IC," [Online]. Available:
http://www.ams.com/eng/Products/Lighting-Management/LED-Driver-ICs/AS1116.
[Accessed 13 2 2013].
Cree, “Cree® PLCC4 3 in 1 SMD LED CLV1L-FKB,” [Online]. Available:
http://www.cree.com/~/media/Files/Cree/LED%20Components%20and%20Modules/HB
/Data%20Sheets/CLV1L%20FKB%201238.pdf. [Accessed 13 2 2013]
[3]
[4]
[5]
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Appendix A: System Block Diagram
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Appendix B: Schematic
Microcontroller hub and
communications
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Hall Effect Sensor Array
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RGB Display Array
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7Segment Display Array
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Power
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