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P12302
02-##-2012
MSD II
SYSTEM DESIGN REVIEW
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ANDY MIDDLETON
BRIAN RELLA
HYUN JIN KIM
INTRODUCTION ABOUT THE PROJECT
Objective Statement for MDS Project # 12302
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The objective of this project is to design and implement a photodiode
array for use in an FTIR multi-touch device. The design must also
incorporate all the necessary circuitry and programing to convert the
data collected (IR light striking the photodiodes) into a digital matrix
and to send the data to a PC via a USB connection.
The main concern will be to increase the SNR in order to improve
reliability and performance by increasing the immunity to ambient IR
light sources. To achieve this, one or more techniques will be
implemented.
CUSTOMER REQUIREMENTS
• 8x8 implementation of passive pixel array.
• An embedded signal designed to differentiate the touch
signal from background noise.
• Minimum of 5mm interpolated touch precision.
• Detect 6 simultaneous finger placements.
• Complete scan of array within 10ms
• Improvement of Signal to Noise Ratio
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• Product shall communicate over a USB connection.
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SPECIFICATIONS
TEST PLAN
1) Inspect
- check every parts of soldering and collect order
2)
-
Component Function
Make sure every parts are working well
Test each component and get the data that we expected
Using multi-meter to measure individual components when we get error.
3) Communication
- Check all the parts are connected together and communicate each other.
4) Desired Input
- Check the range of input and output
- Check the signal to noise characteristic and signal characteristic
5) Data Collection
- Collect the data after we test final PCB component.
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6) Full operation
- Confirm the final data
Probability
(1-5)
1=very low
2=low
3=moderate (design
change)
4=serious
3=moderate
4=high
5=severe (Health
Hazard)
5=very high
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RISK ASSESSMENT
Severity (1-5)
1=minor
2=mild
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RISK ASSESSMENT
SYSTEM DESIGN RISKS REVISITED
1. Missing our budget by purchasing parts that cannot meet our needs.
-Small amounts of parts have been ordered and tested prior to investing in the full order to make best decision
on optimal parts
→ order enough amount of parts and keep those in the box safely.
2. Too much confidence in a concept that does not work.
-Concepts have been researched and tested. The most appropriate concept of modulating the known
infrared LED signal and using signal processing to remove background noise was selected.
→ check every components when we put those on the circuit board and test each components which
get expected values.
3. Errors on manufactured PCB design that are irreversible.
- Prototype board testing of components prior to PCB layout has been started and will be completed prior to the
manufactured PCB order.
→ when we design and order the PCB layout, order enough parts. When we get them, check those
components which get the reasonable value.
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4. Components that do not function as advertised, which would result in budget and time issues.
-Extra parts will be ordered to make sure there are enough parts that work properly. A variety of parts have also
been ordered and tested.
→ check the parts which work properly when the parts are delivered.
5. Team member becomes ill or unable to contribute to the project resulting in overload on other
team members.
-This risk is difficult to prevent but over the breaks we will get additional work done so that we are ahead of
schedule and communicate any possibility of problems occurring ASAP.
→ members do not forget their responsibility and try to keep their health during project period.
BUDGET : BILL OF MATERIALS
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→See appendix
FEASIBILITY ANALYSIS
The project will detect a known infrared
signal as well as a known noise and
measure an improved the signal to noise
ratio reduction from the previous FTIR
detection system.
A photodiode array will be used to detect
the infrared signal and the data array will
be detected by a MCU
The microcontroller will be used to scan
the photodiode array, control the ADC, as
well as filter and detect amplitude of the
stored results. The array scan will be
output to image file format via an Arduino
board USB to a computer.
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The feasibility of the system will be
explained and presented throughout this
presentation.
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SAMPLING TIMING
TEST PROCEDURE
Embedded Sinusoidal Signal Testing
Objective:
The goal of this test procedure is to identify the optimal frequency of the
embedded signal used to power an infrared LED that has the least amount of
harmonics. The range of frequency will be verified that they have very little
distortion associated with them.
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Introduction:
The circuit will be comprised on a photodiode, infrared LED, and a resistor
and assembled on a breadboard. A varying frequency sinusoidal input signal
will be fed to the LED through the use of a waveform generator. The output
from the photodiode will be observed with an oscilloscope and the waveform
will be captured for each frequency input.
The photodiode will be angled directly toward the photodiode. The setup
will be placed inside a dark enclosed box to reduce as much background
infrared radiation (ambient light) as possible. The outputted signal will be
used for harmonic Fourier analysis.
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CIRCUIT BOARD LAYOUT
SIGNAL TO NOISE IMPROVEMENT
The signal detection of the previous FTIR waveguide system
were compared to that of an equivalent signal level from infrared
LEDs.
The infrared glow light was be used as a known level of noise in
both setups as background radiation. For signal detection
measurements, the detected signal were be imported into Matlab
as a data array for analysis.
Signal to Noise ratios were determined and based on the
subtraction of the noise level from the signal to remove as much
of the known noise as possible.
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This setup simulates the improvements that the effects of
sampling a modulated signal has on the signal to noise ratio.
Noise
Noise + signal
Noise + signal – Noise
Prior to having the hardware and software functioning, a simulation of the concept was
conducted using the FTIR multi-touch project, for detection of an infrared signal with a
known high noise level. First a known noise was created, then a signal was then added and
through the use of Matlab the noise was subtracted resulting in the remaining signal.
The waveguide edge lit IR LED frequency range differs from the frequency range of the
matched IR LEDs and photodiode frequency range of our project. This results in direct
comparison of SNR comparison between the FTIR project and our project.
SNR Data: Test Configuration
•
SNR improvement was tested using double correlated sampling.
Known levels of IR Noise were introduced and filtered from a known IR
Signal. The Noise was increased to a maximum in order to test the
limits of capabilities of the project.
Low Level (Florescent) IR Noise
•
The low level IR from the florescent
room lighting was used. The data
array was converted to greyscale for
visual comparison.
nd
2
•
IR Source Noise
A 2nd IR source was introduced to the setup to increase the
level of IR Noise. This 2nd source simulated a background
interference such as a light in the room, with a more focused
specifically located noise impact. A 2nd un-modulated IR LED
was added in order to create the results.
High Level (Saturated) IR Noise
• The sheet of paper was removed
so that the grow light saturated
the photodiode array, simulating
maximum background IR noise.
• The physical IR LED blocked the grow light
from saturating photodiodes in the line of
sight, which enables the correlated double
sampling to be effective. This is comparable
to the effects of a finger touch in an FTIR
touch screen configuration.
SNR Improvement
• The detection of the IR LED Signal despite any
the range of IR Noise was achieved, through
correlated double sampling.
• The detection of the signal during a saturated
level was achieved unlike in an FTIR
configuration, where signal detection is
impossible.
5MM TOUCH PRECISION
The 5mm interpolated touch precision requirement has tested and met with the use of a
caliper. The caliper and photodiode array were positioned in fixed coordinates, with only
the caliper probe able to move. The LED was positioned on the probe, which was then
slide horizontally (x) over the array, on a fixed y and z plane. The probe distance traveled
0.2 inches or 5mm shown in Figure 9. Figure 10 shows the images of the IR signal before
and after the movement, which shows that the touch precision requirement was indeed
met.
Start
Actual
End
Change
X (mm)
Y (mm)
X (mm)
Y (mm)
dX(mm) dY(mm)
80.01
0
74.93
0
5.08
0
33.528
60.2996
41.8338
60.2488
-8.3058
0.0508
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Interpolated
SIMULTANEOUS
TOUCH SIMULATION
The specifications call for at least 6 simultaneous detections,
which can be justified by the touch precision compared to the size
of the photodiode array. Since 2 simultaneous signals are
detected in an area less than one third the area of the total
photodiode array, it can be inferred that at least 6 touches can be
detected.
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Since our project does not have a waveguide, multi-touch
capabilities cannot be directly tested. However, since the entire
array can sense any IR signal at any time, a test can be used to
simulate the ability to detect multiple signals. Using a second
known IR LED signal simultaneously in a different location from
the first IR LED shows the detection capabilities.
CONCLUSION/DISCUSSION
The embedded IR Signal detector met all specifications and
requirements. It will be interesting to see future work
where it is used in conjunction with an FTIR setup.
Looking back, there are many things that went well, and
some things that could have gone better. The hardware
and software worked together, which was good, however
some of the design aspects were done in a hurry to keep
on schedule.
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Given additional time, a new layout would be designed and
implemented with slightly more advanced software. This
project was a great learning experience, not just for the
technology aspect, but also for the real world industry-like
group experience.
ACKNOWLEDGEMENTS
-Mark Baily and the previous work from the FTIR multi-touch
project #11302 team
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-Alex Coleman for working with us on the software portion for
the microcontroller
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SCHEMETIC OF TEST CIRCUIT: NO
AMPLIFIER
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SCHEMATIC: PHOTODIODE ARRAY WITH
OPA727
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SCHEMATIC: PHOTODIODE ARRAY WITH CURRENT
MIRROR
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SCHEMATIC: PHOTODIODE ARRAY WITH LMP7711
COMPONENT SELECTION TRANSISTOR
Transistor
BSS123 - N-Channel Logic
Level Enhancement Mode
Field Effect Transistor
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→ we pick this because, these products have
been designed to minimize on-state
resistance while provide rugged, reliable, and
fast switching performance.
COMPONENT SELECTION PHOTODIODE
Photodiode
BPW 34 FASR
We pick this because, diode was selected for its desirable open circuit voltage
and detection limit.
Unfortunately it is available only in a reverse gullwing package.
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(the circuit which is upside down)
Component selection – Microprocessor
Microprocessor
→We pick this because of
High-Performance 32-bit RISC CPU:
• 80 MHz maximum frequency
• Single-cycle multiply and high
performance divide unit
Analog Features:
• Up to 16-channel, 10-bit Analog-to-Digital Converter:
- 1 Msps conversion rate
- Conversion available during Sleep and Idle
• Two Analog Comparators
Microcontroller Features:
• Operating voltage range of 2.3V to 3.6V
Peripheral Features:
• USB 2.0-compliant full-speed device and
On-The-Go (OTG) controller
• Internal 8 MHz and 32 kHz oscillators
• Separate PLLs for CPU and USB clocks
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• High-speed I/O pins capable of toggling at up to 80 MHz
PHOTODIODE
Photodiode
BPW 34 FASR
Unfortunately it is available only in a reverse gullwing package.
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(the circuit which is upside down)