smart quill full report

[project report tiger]

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ABSTRACT
Developed by British Telecom,Smart Quill is claimed to be biggest revolution in handwriting after the invention of pen.
Smart Quill refers to a futuristic computer pen which has a number of features like:
¦ it has its own memory
¦ it can be used to write on any flat surface(not only on paper)
¦ options are provided for editing and sending the text via e-mail and so on.
¦ it is password protected.
Smart Quill uses accelerometer sensors which measure the acceleration experienced by the sensor and anything to which the sensor is attached. The acceleration experienced by a test mass (proof mass) is converted into electrical signals which are reprocessed to retrieve the orginal text or picture.This pen finds many applications in video conferencing , as a note taker or as a contact data base and in various other fields.The earlier prototype of the pen has been developed and a number future works are going on in this direction .Surely Smart Quill is the technology of the future.
INTRODUCTION
Sensors allow detection,analysis and recording of physical phenomenon that are difficult otherwise to measure by converting the phenomenon into a more convenient signal.Sensors convert physical measurements like displacement,velocity acceleration ,force, pressure etc into electrical signals.The value of the original physical parameter can be back calculated from the appropriate characteristics of the electrical signal.Electrical outputs are very convenient because there are well known methods for filtering and acquiring electrical signals for real time or subsequent analysis.
Sensor size is often important and small sensors are desirable for many reasons including easier use ,a higher sensor density and lower material cost.A revolution in microfabricated sensors occurred with the application of semiconductor fabrication technology to sensor construction .By etching and depositing electrically conductive and non conductive layers on silicon wafers ,the sensor is created with the electrical sensing elements already built into the sensor.The product created using these techniques is called Micro Electro Mechanical Systems or MEMS.
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ACCELEROMETER SENSORS
Accelerometer sensors measure the acceleration experienced by the sensor and anything to which the sensor is directly attached. Accelerometer sensors have many applications.
When working with accelerometers in the earths gravitational field there is always acceleration due to gravity .Thus the signal from an accelerometer sensor can be separate into two signals : acceleration from gravity and external acceleration . Acceleration from gravity allows measurement of the tilt of the sensor by identifying which direction is down.By filtering out the external acceleration the orientation of a 3-axis sensor can be calculated from the accelerations on the 3 accelerometer axis Orientation sensing can be vary useful in navigation .
The goal of the sensor is to measure the 3-d acceleration of human hand motion with adequate accuracy and precision,necessary band width for normal human motion and the amplitude range for the highest normal acceleration.
At the same time the physical presence of the sensor should not alter the hand motion The application of measuring something sensitive to external mass like the human hand requires the accelerometer sensor to be extremely small and light weight.
By measuring the acceleration of the pen as the user writes the text ,the pen decodes the acceleration into words and sends the signal into the computer.Such a computerized pen is more convenient and portable than a digitized tablet , which measures the location of the tip of a pen on a pad.
BASIC THEORY OF OPERATION
Accelerometer sensors convert either linear or angular acceleration to an output
signal.
Accelerometer sensors use Newton's second law of motion F = m.a
by measuring the force from acceleration on an object whose mass is known .There are many ways to measure the force exerted on the mass,called a proof mass but the most common method used in accelerometer sensors is measuring the displacement of the mass when it is suspended by springs.
Proof Mass
Fixed Reference Diagram of differential capacitive layout
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Forces acting on the proof mass include force from external acceleration,the force from damping (propotional to velocity)and the restorative force of the spring (propotional to position).
In Accelerometer sensors operating far from the resonant frequency of the mass-spring system, the effect of damping can be largely ignored.Some high precision accelerometer sensors operate near the resonant frequency to mechanically amplify the displacement from acceleration.
For sufficiently small displacements ,the spring constant K(x) can be assumed to be a constant.In equilibrium when the mass is not moving , the restorative force exerted by the spring is equal to the force from acceleration on the proof mass.The displacement of the spring,x,can be converted into an electrical signal by a variety of methods.
ARCHITECTURE AND WORKING
Electronics Overview
The MTL accelerometer sensors converts acceleration into changing capacitors. An electrical circuit is used to convert the differential signal into an electrical signal for computer acquisition.
Fingertip PCI
Arm PCB (Analog Board)
Accelerometer sensor
LVDT Signal Conditioners
ADC
Buffers
Anti aliasing Filters
Line Driver
/
FIFO Buffer
Line Driver
Clock
Counter
LapTop
Base PCB ( Digital Board)
Block diagram of sensor electric circuit.
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There are three accelerometers in the fingertip sensor to sense three dimensional motion. Each accelerometer is connected to a linear variable differential transformer signal conditioner IC,which converts the differential capacitance into an analog voltage-proportional to the proof mass position in the die. Proof mass position is proportional to external acceleration by the springs attached to the proof mass.
The LVDT signal conditioner has a sinusoidal voltage output connected to the proof mass. The corresponding voltages on the dual capacitor electrodes will also be sinusoidal, but the amplitudes will vary depending on the spacing between the proof mass and the capacitor electrodes. Voltage followers used on the fingertip sensor buffer the capacitive signals immediately out of the accelerometers to prevent the excessive noise in the wires between the fingertip and the LVDT signal conditioners on the nearby analog signal processing board.
The analog outputs of LVDT signal conditioners from each acceleration axis are passed through anti-aliasing filters and then to separate channels of a 4-channel 16-bit Analog to Digital converter (ADC) .The serial digital output from the ADC is passed to a first-in-first-out (FIFO) buffer on the digital board, which both buffers the data and converts the serial signal into a parallel signal. The parallel data from the FIFO is sent into the parallel port of a laptop computer and a program displays and stores the data on the laptop.
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LVDT SIGNAL CONDITIONER IC
An LVDT signal conditioner IC is used to convert the accelerometer differential capacitance signal into an analog voltage proportional to the acceleration. LVDTs are used in manufacturing and robotics as precise linear position sensors. An LVDT is a set of three wire-coils collinear with each other. One central coil is the primary of the transformer, and the other two are secondary coils. A paramagnetic metal rod is placed partially in the core of the coils and allowed to slide freely in out of the cores. As the position of the metal slug moves , the relative transformer ratios between the primary and secondary coils will change. The LVDT signal conditioner provides the AC excitation voltage to the LVDTs primary and outputs n analog signal proportional to the position of the metal slug by measuring the relative secondary voltages.
Paramagnetic Sulg
Primary Coil
+
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V secondary 1
+
V secondary 2
Secondary Coil 1
Secondary
Coil 2
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The equation for voltage across a transformer coil is that the ratio of voltages is equal to the ratio of coil turns. The presence of a paramagnetic element in the core of the secondary coils increases the magnetic flux density and thus increases the effective turns ratio, increasing the coil voltage.
The LVDT signal conditioner IC produces an AC voltage of constant amplitude connected to the LVDT primary coil. The amplitude of two secondary coil output voltages vary depending on the metal slug position. The signal conditioner takes the voltages vary depending on the metal slug position. The signal conditioner takes the voltages from the secondary coils and calculates the voltage magnitudes. The output of the signal conditioner is an analog voltage linearly proportional to the position of the slug in the core of the LVDT.
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ANTI ALIASING FILTER
Frequency (Hz)
The anti-aliasing filters are four pole butterworth filters with a cutoff frequency of 45Hz, allowing frequencies upto 25Hz to be measured without distortion while still removing some 60H z noice from the environment. The butterworth topology was selected because it works well to solve the opposing goals of preserving the signal upto 25Hz and removing as much noise as possible at 60Hz and above. Preserving the signal below cutoff frequency is best done using a Bessel filter,and removing noice above the cutoff frequency is best done with an elliptical filter, but the butterworth filter is a good compromise between the two.
ADC
The filtered analog signal leaves the Butterworth filter and enters the ADC ,a 16 bit successive-approximation switched capacitor ADC.The ADC operates at DC ,meeting the minimum measurable frequency specification of 0.1 Hz. Just prior to entering the ADC the signal passes through a final RC low pass filter with a cutoff frequency of about 32 KHz to remove any noise in the signal either injected from the active anti-aliasing filter or added in the final trace between the filter and the ADC.
ADC
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Equivalent ADC input electrical circuit
The resistance in the RC filter was chosen to be 50 ohm. A low series resistance is important because the ADC uses a switched capacitor method of sampling the signal. When the capacitor inside the ADC is switched to sample the signal, if the series input resistance is high then the voltage on the capacitor will drop as the capacitor charges and when the capacitor voltage is converted the voltage will be lower than the correct voltage.
Data, DataClk
Address Bit 1
Address Bit 0
Read ./Convert
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Read Ch 0 Read ch 1 Read Ch 2
Ch 0 Ch 1 Ch 2
Read Ch3
Time
Timing Diagram of ADC Functions
The ADC has four channels - three are used for each of the three-accelerometer channels and the fourth is used as the parsing channel. The fourth is railed to above the valid input range so the ADC output for that channel will always be maximum. As the four channels are sampled in a sequence in an endless loop each time a channel is the maximum value the data acquisition program can recognize that channel as the parsing channel and correctly process the following three data channels correctly.
The ADC makes its channel selection by two channels from the digital board The two signals are created by a two-bit counter which steps through the four channels one at a time. There is also a read/convert signal sent to the board which alternatively triggers the ADC to acquire an analog voltage from the appropriate channel and then convert the signal and output the serial digital result.
A 4.5 MHz clock internal to the ADC clocks out the ADC digital output. The ADC output is two brief signals after conversation is complete: the data signal and the clock signal. The clock signal is sixteen consecutive clock signals for the sixteen bits of data. The data, least significant bit first, has each bit valid on the falling edge of each clock pulse.
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The two ADC digital output signals are passed into a buffering line-driver/line-receiver, the 74LS244 (Fairchild semiconductor). The ADC digital outputs are buffered to provide the necessary power to drive the cable between the analog and digital boards. The buffer also receives the read/convert and channel-select signals from the digital board and sends them to the ADC. The line-driver has a maximum frequency of 80MHz, which is more than fast enough for the 4.5 MHz signal from the ADC. The cable connecting the analog and digital boards is a standard 9-conductor serial cable with DB9 connectors at each end.
THE DIGITAL BOARD
The primary function of the digital PCB is converting the serial digital data from the ADC to a parallel signal suitable for passing into a computer through the parallel port. The-other important functions of the digital board are creating the clock and channel signals for the analog board, and connecting to the power source and delivering the power to the analog board.
The lower copper layer has a very large ground plane to minimize noise. A 9-pin connector receives the cable from the analog board, and a Centro nix 36- pin connector connects to a standard printer cable running into the parallel port of the laptop computer. A small section of header is used to connect to the power supply, delivering +5 V, -15V and ground
The key element on the digital board is a first-in-first-out (FIFO) buffer the IDT72132L50P (Integrated Device Technology) The FIFO buffer has an externally clocked serial input and an 8-bit parallel output, with 2, 048 bytes of memory. Another 74LS244 line-driver/line-receiver on the digital board receives the ADC data and locks signals from the analog board and sends them directly to the FIFO input. The sixteen bits of serial data fill up two successive bytes in the FIFO memory. The maximum serial input rate is 40 MHz, which is more than adequate for the 4.5 MHz signal from the analog board.
The FIFO has four output pins that are flags to show the available FIFO memory. The computer software monitors these flag signals and when the FIFO has data in its memory the data is recovered. The laptop sends a read signal on a control line of the parallel port to the digital board. The signal is buffered through the 74LS244 to avoid spurious read requests, and then sent to the read line of the FIFO. When the read line goes low the first byte of data is displayed at the eight output registers of the FIFO. When the read line goes high and then low again, the next byte of data is displayed. To access all sixteen bits of the ADC data, two successive reads are required. The output registers are connected through the printer cable to the parallel port of the computer.
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A clock on the digital board is the source for the channel counter and the read/convert signal for the ADC. The clock is a simple 555 timer 83 national Semiconductor). As mentioned above, the frequency of the clock is variable, but it has a range of 1 to 3.2 kHz and has a duty cycle of 70%. The clock frequency is divided by the number of channels (four) for the sampling rate per channel, and when optimizing the clock frequency the limiting factor is the software's acquisition speed. The FIFO receives 2000 to 6400 bytes per second, which allows the computer software to delay acquiring the data 1 to 0.31 seconds before the buffer overflows and data is lost.
The clock, counter, and inverter are located on the digital board to reduce the required area and weight of the analog board, which is potentially located on the arm. The digital board is located next to the laptop computer, which already fairly large and bulky so the digital PCB is not a significant addition.
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PROGRAM OVERVIEW
A computer program was written in Visual Basic 86 (from Microsoft, Inc) to download, process and display the accelerometer data collected in the first-in-first-out (FIFO) buffer on the digital board. The program was implemented on a laptop computer connected through the parallel port to the digital board of the sensor.
The software is the final component of the complete accelerometer sensor. The program stores and displays the acceleration data from the accelerometer sensor when the sensor is tested or used in a more practical setting
There are three sections to the program. First the data is collected through the parallel port of the laptop computer, which accesses the data in sequential bytes from the FIFO. The data is then processed, which includes diving the data into separate channels for each of the three axes of the sensor and also digitally filtering the data. Finally the data is displayed on the computer screen and optionally stored to disk. The computer program runs sequentially in an endless loop through these steps.
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DATA ACQUISITION
The connection between the laptop computer and the digital board is made with a standard 25-wire printer cable, which has a 36-contact Centro nix connector on the side of the digital board and a 25-contace connection at the computer's parallel port. The connections in the parallel port of a computer are divided into several different groups: eight data lines, four control lines , four status lines, and the remainder are grounds.
The control lines are transmit only: the computer sends out signals on these lines. The status lines are receive only: on these lines the computer receives information from the peripheral (typically a printer). The data lines can be used for transmitting or receiving, and the method of selecting between the two directions depends on the computer hardware-system. The laptop used in this project has a bit in a register inside the computer that can be¬set high or low to respectively receive or transmit data over the data lines.
Defer
Other Defer Functions
Defer
Show FIFO Status
No
Process Data Display & Save data
Flow chart of Acquisition algorithm
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The FIFO buffer on the digital board has eight parallel output registers connected to the eight data lines in the parallel port. There are four FIFO status pins that are memory capacity flags connected to the four parallel port status line, and together indicate if the FIFO is empty, almost empty, less than half full, more than half full, almost full, or full.
The first step to data acquisition is checking the FIFO status lines. If the memory capacity flags indicate the FIFO has data available, a parallel port control line connected to the read pin on the FIFO is switched, loading the next byte of data through the data lines of the parallel port and proceeds on to the next section of the program: processing the data.
Visual Basic programs need to periodically defer use of the computer's CPU to allow low-level processes to run, such as responding to keyboard data entry or mouse clicks. In this program, deferral occurs once each second. Just before the program defers, the computer screen displays the FIFO memory status indicated by the status lines. The program also has other functions it does just before deferring, such as calculating and displaying the rate of data acquisition, which is done by counting the number of bytes downloaded in that second. In addition, if there is no data in the FIFO, the program defers to kill time.
DATA DISPLAY AND STORAGE
This section displays the data, and if the user desires, the raw or filtered data can also be saved. Due to the constraints of the two-dimensional computer screen, the user can select only two accelerometer channels to display at any one time: one on the horizontal axis and
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The user has the option of saving the acquired data two different ways: either the unfiltered raw data after being sorted into the three different channels, or the filtered output data: the same points displayed on the screen. When the user indicates they want to save data, they first create the file to save the data into. After preparing the data file, the user can start acquisition at any time. By keeping a delay between creating the file and staring acquisition, the data that filled the FIFO to overflowing while the dialog box was presented can be processed, and data acquisition can start with the FIFO almost empty.
The display and saving section proceeds if the fitter output is ready to be displayed. If the user has selected saving filtered data, then the filtered data output is scaled and saved as the next line in the data file at this time.
Then the data display is updated. The user selects which of the data channels (A,B or C) to be displayed on the horizontal and vertical axes. In addition, the data on either axis can be negated to flip the data displayed. The user can also select if the data plotted is just the most recent point, or a fading persistence using the last 20 points from the filter. The newest data point is displayed as a line from the center of the display to the point, and the older data can either be displayed as lines from the center or just points.
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Acquire Data Process Data
Defer
Defer Function
Save raw Data
Select Horizontal Vertical Channels
Negate Data if Selected
No
Display Data with persistance if selected
Flow chart Data display and Storage Algorithm.
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ADVANTAGES
1. Smart quill can read on any flat surface (not only on paper)
2. It is password protected.
3. Highly convenient and portable.
4. It can page link to modems, printer etc
DISADVANTAGES
1. It has accelerometer errors.
2. It is inconvenient for persons with hand tremours.
3. Bigger size than a normal pen.
4. Errors are introduced in the system due to thermal variations in the spring.
APPLICATIONS
1. Diary
2. Calculator
3. Alarm
4. Contact database
5. Note taker
6. Calender
7. Receive mobile and pager messages.
8. Video conferencing
9. Classroom lectures
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FUTURE DEVELOPMENTS
That is further developments are doing on re fabrication and reducing the size of the pen. Three dimensional sensors are developing and with the implementation free writing in air can be achieved . Development of light at the tip of the pen helps in easy writing in the dark. Special heat sensors can be implemented which can detect the temperature variations and can act as a heat doctor of the body.
CONCLUSION
Smart quill will be a boon to the users writing in traditional languages. It gives an option for typing and for variety of applications. The day may come when we lose our
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stinctions between the devices we use to interact with our computers and the computer emselves.
REFERENCES
1. Accelerometer Sensor to measure human hand motion - Brian Barkley Graham
2. innovate.bt.com
3. photonics(aUaurin.com
4. howstuffworks.com
CONTENTS
1. INTRODUCTION 06
2. ACCELEROMETER SENSOR 07
3. BASIC THEORY OF OPERATION 08
4. ARCHITECTURE AND WORKING 09
5. LVDT SIGNAL CONDITIONER IC 12
6. ANTI ALIASING FILTER 14
7. ADC 15
8. DIGITAL BOARD 18
9. PROGRAM OVERVIEW 20
10. ADVANTAGES 25
11. DISADVANTAGES 25
12. APPLICATIONS 26
13. FUTURE DEVELOPMENTS 27
14. CONCLUSION 27
15. REFERENCES 28