Finger Mouse Design Review

Chi-Wei Huang, Ting-Fu Chen, Yi-Chun Tseng

TA: Stephen Hall

September 29, 2015

ECE 445

2

Table of Contents

1. Introduction.......................................................................3 1.1 Statement of purpose...............................................................3 1.2 Objectives.................................................................................3

1.2.1 Goals....................................................................................................3

1.2.2 Functions..............................................................................................3

1.2.3 Benefits................................................................................................3

1.2.4 Features................................................................................................3

2. Design................................................................................4 2.1 Block diagram...........................................................................4 2.2 Block description......................................................................4

2.2.1 Power Supply.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4

2.2.2 Gyroscope and Accelerometer.......................................................5

2.2.3 8051 Microcontroller…………………………………………………………………5

2.2.4 Bluetooth Transmission.........................................................................5

2.2.5 Bluetooth Receiver..........................................................................5

2.2.6 Arduino Microcontroller…………………………………………………………………….5

2.2.7 Computer....................................................................................5

2.3 Device Illustration………………………………………………………………….6 2.4 Schematics………………………………………………………………………………6

2.4.1 Microcontroller AT85S91 with Bluetooth module HC-05...................6

2.4.2 Step up converter………………………………………………………………………………8

2.4.3 Gyroscope sensor module with LDO…………………………………………………9

2.4.4 Accelerometer sensor module with LDO………………………………………….10

2.5 Flow chart…………………………………………………………………………….11

3. Requirement and Verification...........................................12 3.1 Table of Requirement and Verification....................................12 3.2 Tolerance analysis..................................................................13

3.2.1 Power Analysis…………………………………….………………………………………….13

3.2.2 Bluetooth transmission distance…………..………………………………………….13

4. Cost and schedule.............................................................14 4.1 Cost analysis…………………………………………………………………………14

4.1.1 Labor……………………….…………………………………………………………………….14

4.1.2 Parts……………………………………………………………………………………………….14

4.1.3 Total cost………………………………………………………………………………………14

4.2 Schedule……………………………………………………………………………15

5. Ethics & Safety issues…………………………………………………..15

6. Reference……………………………………………………………………….16

3

1. Introduction

1.1 Statement of purpose We choose this project because we noticed that presenters always need

somebody to help him/her control the Power-point. Although some of them

can deal with this by a laser pointer. However, if they want to draw pictures,

present a video, or do some other kinds of interaction with the listeners, they

have to walk back to their computer to achieve this, which waste a lot of time

and interrupt the presentation.

So, our idea is to invent a wireless wearable mouse, which is small and light

enough to wear around, while allowing the presenters to control the

computer curser away from their PCs, even without a desk!

1.2 Objectives 1.2.1 Goals

Build a wireless, desk-free mouse which is operated by finger motion

detecting. The control will be more fluent and no longer be influenced by

the rugged bump on the surface.

1.2.2 Functions

This wireless mouse will be a battery-powered device. It can control

the computer cursor by hand motions, including curser “Moving”,

“Clicking” and ”Dragging”.

1.2.3 Benefits

˙ Small, light, and easy to bring.

˙ Wireless and can be operated on any kind of surface, even without a

desk. It will be more convenient for speakers or lecturers to use when they

are on stage.

˙ No wearing and tearing problem of clicking button, that is, longer

lifetime.

1.2.4 Features

˙ Fashion, light and convenient to carry.

˙ Implement convenient controlling shortcuts by pre-defined gestures.

˙ User don’t need to change their old mouse using habits.

˙ Avoid user from “Carpal tunnel syndrome”.

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2. Design

2.1 Block Diagram There are two separate parts in our project. One is on our finger which includes

gyroscopes and Bluetooth transmitter. And the other one including microcontroller

and Bluetooth receiver will connect with the computer. The following figure is a

diagram of our whole system. The solid line represents the power path and the

dotted line means the signal path.

Figure 2.1

2.2 Block description 2.2.1 Power Supply

We are considering using 3V button cell (watch battery) to serve as basic power

supply for the device circuits. Gyroscopes and accelerometer need 3.3V power

Power

Signal

3.3V

Battery Step up

Converter LDO Gyroscope

LDO Gyroscope

LDO Accelerometer

8051

Microcontroller

Bluetooth

Transmitter

Computer

USB

Arduino

Microcontroller

Bluetooth

Receiver

3V 5V 3.3V

5V 5V

3.3V

5

supplies whereas 8051 microcontroller and Bluetooth transmitter need 5V

power supplies. The voltage of watch battery is 3V and will be boosted to 5V by

a Step-Up convertor to supply 8051 microcontroller and Bluetooth transmitter.

Meanwhile, we use a LDO (Low Drop Out Regulator) to transfer the voltage to

3.3V to supply gyroscopes and accelerometer.

2.2.2 Gyroscope and Accelerometer

We plan to put two gyroscopes and one accelerometer on user's fingers.

Gyroscope1 is on the first finger and others (Gyroscope2 and Accelerometer)

are on the middle finger. Gyroscopes will detect the angular velocity whereas

accelerometer will measure the acceleration of user’s fingers. All of them will

measure the user’s motion and be wired as inputs to the Bluetooth transmitter

and will give raw data to it.

2.2.3 8051 Microcontroller

8051 microcontroller is before the Bluetooth transmitter. It will receive the raw

data from sensors and control Bluetooth transmitter to transmit it.

2.2.4 Bluetooth Transmitter

Bluetooth transmitter on the user's hand will be controlled by an 8051

microcontroller and transmit the raw data from sensors that are gyroscopes and

accelerometer to the Bluetooth receiver.

2.2.5 Bluetooth Receiver

The Bluetooth receiver will receive the data from transmitter and then pass it to

the microcontroller (Arduino). Its power will be supplied from the computer via

the USB.

2.2.6 Arduino Microcontroller

Arduino microcontroller monitors the data from the Bluetooth receiver. After

receiving and analyzing the data, Arduino will transfer it to a specific form that

can be used and then transmit it to the computer to control the cursor. 5V

power supply of the Arduino will be provided by the computer through USB.

2.2.7 Computer

Computer will supply 5V voltage to Arduino Microcontroller and Bluetooth

receiver via USB. On the computer, we will write a Java program to

communicate with the Arduino microcontroller and deal with the data from it.

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The Arduino IDE itself is written in Java, and it can communicate to the serial

port via the RXTX Java library. That library is very similar to the Java

Communications API extension. After getting the data, the Java program will

control the cursor according to the data.

2.3 Device Illustration

Figure2.3

2.4 Schematics 2.4.1 Microcontroller AT85S91 with Bluetooth module HC-05

Figure2.4.1

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The AT85S91 is a low-power, high-performance CMOS 8-bit microcontroller with

4K bytes of in-system programmable Flash memory and 32 input pins. In our circuits,

it serves as a data processer and Bluetooth transmitter controller. It has 4V~5.5V

operating range, we choose 5V and connect it to the VCC pin.

- RST pin should be low for all the time because we don’t need to reset our pins,

we connect a capacitor and register circuit to avoid floating voltage.

- XTAL1, XTAL2 are connected to the inverting crystal oscillator amplifier circuit.

XTAL1 is the input to the internal clock operating circuit while XTAL2 is the

output form the oscillator.

We need to decide how long the internal Timer1 clock (TH1) should be set by

calculating from the following formula:

Baud rate =2SMOD

32× 𝑇𝑖𝑚𝑒𝑟1′s overflow rate

=2SMOD

32×

𝑜𝑠𝑐𝑖𝑙𝑙𝑎𝑡𝑖𝑛𝑔 𝑓𝑟𝑒𝑞

12 × [256 − 𝑇𝐻1]

The TX/RX Baud rate of the HC-05 Bluetooth module is 38400 bps, so we set the

SMOD = 1 to set the same Baud rate in our AT89S51 MCU. Knowing the baud

rate, we can calculate the TH1 now:

TH1 = 256 −21 × 𝑜𝑠𝑐𝑖𝑙𝑙𝑎𝑡𝑖𝑛𝑔 𝑓𝑟𝑒𝑞

384 × 38400

If we choose oscillating frequency = 11.0592MHz, then TH1 = 254.5, which is

hard to be precise in Hexadecimal.

So, we choose oscillating frequency = 22MHz, then TH1 = 253 = 0xFD, which has

smaller error than the above one.

- P3.0 and P3.1 are the RXD and TXD pins, we connect them to the corresponding

TX/RX pins of the HC-05 Bluetooth module to do serial data communications.

- Port0 and Port2 are used as input ports. While P0.0~P0.2 reads the digital

outputs from the gyroscope1, P0.3~P0.5 reads the outputs from gyroscope2,

and P2.0~P2.2 reads the outputs from the accelerometer.

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2.4.2 Step up converter

Figure2.4.2

L6920D is a high efficiency boost converter which accept the input voltage

range from 0.6 to 5.5V. We want to use CR2032 Lithium coin cell battery which

provide 3V output voltage. To fit the operating voltage of microcontroller and

Bluetooth transmitter, we use this converter to make 5V output voltage.

- Lx: Connect with input inductor and battery voltage, the recommended

value of input inductor is form 5uF to 40uF. Small inductor have smaller

size and fast transient response but the output ripple would be bigger. In

our project, we need to make everything smaller so we just choose 10uH.

- LBI: Low battery voltage detection. The input voltage will compare the

build-in bandgap voltage (1.23V), LBO_ would be high if the input voltage

is smaller than 1.23. Actually, our battery would provide 3.2V at the

beginning and drop to about 2.5V when it is running out. If the battery

voltage become smaller than 2.7V, we want to light a LED and remind the

user to change the battery. So the ratio of R1 and R2 would be:

R1

R2=

2.7 − 1.23

1.23= 1.195

We just choose R1 = 1.2MΩ and R2 = 1MΩ

- Vref: The build-in band gap voltage. The value is about 1.23V. We just

connect a 100nF capacitor for filtering high frequency noise.

- F.B.: L6920D can adjust the output voltage to be 3.3V or 5V by the

feedback controlling. We just connect it to GND to generate the 5V output

voltage. We select a big R4 (1M) to minimize consumption.

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- SHDN_: Shut down pin. When it is lower than 0.2V, L6920D would be

disable. We use a switch to control the power of the device.

- LBO_: When low battery voltage been detected, LBO_ goes high and we

can connect with LED to make a warning signal.

- Vout: The output voltage would be 5V with very small ripple. The

recommended range of inductor is from 10uF to 100uF. If we want to

improve the conversion efficiency, low ESR capacitor is needed. We just

choose Panasonic EEFCDJ470R, which is 47uF with 18mohm ESR.

2.4.3 Gyroscope sensor module with LDO

Figure 2.4.3

We use this module to detect the angular rate of finger. Basically, the gyroscope

L3GD20H need 3.3V to operate, but we only convert battery voltage to 5V to supply

microcontroller and Bluetooth transmitter. We can use 5V voltage on this module

because of the LDO. The output format is I2C and 16-bit data per axis. This sensor

and relative circuit will be equipped on fingers, so the size is very important. The

dimensions of these module: 13×23×3 mm. It is small enough for us to use.

- SDA: Level-shifted I2C data line. This port will connect with the

microcontroller.

- SCL: Level-shifted I2C clock line. This port will connect with the

microcontroller too.

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- CS: This port can adjust the communication format between I2C and SPI. We

use only I2C to transmit data, so we will pull up to VDD.

- SDO: 3.3-logic-level input to determine I2C slave address. Also connect to

microcontroller.

2.4.4 Accelerometer sensor module with LDO

Figure 2.4.4.1

We use this module to detect the acceleration. Just like the gyroscope module,

there is a build-in LDO allow us to use 5V voltage to operate the sensor. The

dimensions of this module: 10×23×3 mm. It is also small enough for this project.

- SDA: Level-shifted I2C data line. This port will connect with the

microcontroller.

- SCL: Level-shifted I2C clock line. This port will connect with the

microcontroller too.

- CS: This port can adjust the communication format between I2C and SPI. We

use only I2C to transmit data, so we will pull up to VDD.

- SDO: 3.3-logic-level input to determine I2C slave address. Also connect to

microcontroller.

To sum up, there will be three I/O pin connected with the microcontroller for

each sensor. And we use 2 gyroscopes and 1 accelerometer, there will be 9 wires

connect the sensors and microcontroller except the power supply.

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Figure 2.4.4.2

2.5 Flow Chart

Implement cursor

“Move” motion

Bluetooth Receiver

receives data

Arduino microcontroller

signal processing

YES

Click Down NO

Implement cursor

“Click” motion

8051 microcontroller

processes data

Start

Gyroscope/Accelerometer

start detecting signal

ON

Power switch

ON/OFF

OFF

Bluetooth Transmitter

sends data

YES

Click Up

NO

Implement cursor

“Drag” motion

Move

YES

NO

YES

NO

Move

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3. Requirements and Verification

3.1 Table of Requirements and Verification

Requirement Verification points

1. Power Supply

a. DC/DC converter should be

able to provide 5V +/- 0.25V

output voltage for bluetooth

transmission and

microcontroller.

b. DC/DC converter should be

able to provide 30mA +/- 3mA

output current.

c. LDO embedded in the sensor

module should provide 3.3V +/-

0.2V output voltage.

1. Power Supply

a. Use digital multimeter to

measure the output voltage,

and it should read 5V +/- 0.25V.

b. Use digital multimeter to

measure the output current

after conversion, and it should

read 30mA +/- 3mA.

c. Use digital multi-meter to

measure the output voltage of

the LDO, and it should read

3.3V +/- 0.2V.

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2. Sensors

a. Gyroscopes should be able to

measure 3-axis angular rate at

minimum value 30°/s and

maximum value 245°/s.

b. Accelerometer should be able

to measure 2-axis (no z axis)

acceleration at minimum value

0.1m/s2 maximum value 3m/s2.

2. Sensors

a. Rotate the gyroscope at

angular rate 30°/s and 245°/s,

we can read the correspond

data value from the sensor.

b. Move the accelerometer at

acceleration 0.1m/s2 and

3m/s2, we can read the

correspond data value from

the sensor

30

3. Microcontroller External Clock

a. The external crystal oscillator

should provide 22MHz clock

frequency for the AT89S51

MCU to assure the baud rate is

correct for the Bluetooth

transmission. Due to the timer-

recounting per 10bits

transmitted, 2%~3% frequency

error is still tolerable.

4. Microcontroller External Clock

a. Connecting the VCC, GND to

the inverting oscillator

amplifier and use an

oscilloscope to check the

output frequency is about

22MHz ±400KHz.

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4. Bluetooth Transmission

a. The Bluetooth transmitter

4. Bluetooth Transmission

a. Transmit data by 25

13

should catch the data and

transmit it to the

microcontroller in baud rate

38400 (bps).

b. The Bluetooth transmitter

should be able to transmit data

within 10 meters.

microcontroller to Bluetooth

receiver and transmit it back to

controller. We should receive

and transmit 38400 bits per

second.

b. Take the transmitter 10 meters

away and check whether the

receiver could catch the data.

5. Driver

a. Driver on computer should

catch the specific signals and

operate the cursor properly.

5. Driver

a. Transmit data to the computer

by microcontroller and observe

the movement of the cursor.

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3.2 Tolerance Analysis

3.2.1 Power Analysis

The capacity of our battery is 220mAh. To operate all the sensor and

microcontroller, it need about 30mA. We can use a battery for about 7.3 hours. It

is an acceptable value but we could increase the battery live by using one more

battery. In the ideal condition, we could use our device for about 14.6 hours. If

the current goes 30% higher than we expect, we can still use the device for 11.2

hours.

3.2.2 Bluetooth transmission distance

One of the features of our project is wireless. Therefore, the distance of

Bluetooth transmission is very important.

According to the datasheet, the Bluetooth receiver has typically -80dBm

sensitivity and up to +0dBm RF transmit power. And as we know that Free-space

path loss formula is

FSPL(dB) = 20 log10(𝑑) + 20 log10(𝑓) − 27.55

where

d is our distance between the transmitter and receiver in meter, and

f is the signal’s frequency in MHz which is 2400MHz

thus

80 = 20 log10(𝑑) + 20 log10(2400) − 27.55

d ≈ 100(m)

That means we can use this mouse in 100 meters.

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4 Cost and Schedule

4.2 Cost Analysis

4.2.1 Labor

Name Hourly rate Total Hour Invested Total = Hourly Rate *

2.5 * Total Hours

Invested

Chi-Wei $35.00 160 $14000

Ting-Fu $35.00 160 $14000

Yi-Chun $35.00 160 $14000

Subtotal $52000

4.2.2 Parts

Item Where to use Quantity Cost

Gyroscope L3GD20 Sensor 2 $19.9

Accelerometer LSM303D Sensor 1 $9.95

DC/DC converter L6920D Power convertor 2 $4.96

Battery holder Power supply 2 $3.00

Microcontroller

Arduino UNO

Receiver circuit 1 $20

Microcontroller AT89S51 Transmitter circuit 1 $1.99

Bluetooth module HC-05 Receiver/

Transmitter circuits

2 $7.8

Resistor 10KΩ US0204/7 Transmitter circuit 1 $0.05

Crystal Oscillator 22MHz

SG-615

Transmitter circuit 1 $0.25

Capacitor 10uF C5B25 Transmitter circuit 1 $0.5

Capacitor 33pF AE86 Transmitter circuit 2 $0.76

Capacitor 47uF EEFCD0J470R Power convertor 2 $0.88

Inductor ELL6RH100M Power convertor 1 $0.84

Subtotal $70.88

4.2.3 Total Cost

Labor + Parts = $52000 + $70.88 = $52070.88

15

4.3 Schedule

Date Chi-Wei Ting-Fu Yi-Chun

9/21 Prepare project proposal and research on components

9/28 Design 8051 MCU and

Bluetooth transmission

circuit

Test gyroscopes,

accelerometer and

Arduino

Design power supply and

voltage converter circuits

10/5 Test for Bluetooth

transmission tolerance

Algorithm of dealing

with data from sensor

Research on I2C

communication protocol

10/12 Design and order PCB

of sensors, MCU and

transmitter

JAVA Coding for driver

between Arduino and

computer USB

Design and order PCB of

power supply and voltage

converter

10/19 Assemble all parts, debug and test the device

10/26 Assemble all parts, debug and test the device

11/2 Prepare for mock demo

11/9 Debug after mock demo Begin the final paper

11/16 Prepare demo Prepare final paper

11/23 Thanksgiving break

11/30 Finalize the presentation and demonstration

12/7 Finalize the final paper

5 Ethics & Safety issues

It is very important to follow the rules of the IEEE code of Ethics while we are

designing anything. As an engineer, we can't just develop new products and then

ignore the safety, health and welfare of the public. There are also various aspects

that we must keep in mind all the time.

The first one of those aspects is that we have to disclose promptly factors that

might endanger the public or the environment. Meanwhile, we also must avoid

injuring others, their property, reputation, or employment by false or malicious

action. In other words, it's our responsibility as engineers to confirm our product

16

is safe enough for people to use. A couple of safety issue of our product would be

the circuit short and eventually leads to burn while user is using. Therefore, while

designing, we have to make sure that the circuit would not be short.

6 Reference

1. Air mouse

https://www.youtube.com/watch?v=m6j8SFJs4lA

2. AT89S51 datasheet

http://www.keil.com/dd/docs/datashts/atmel/at89s51_ds.pdf

3. HC-05 Bluetooth-to-Serial Module datasheet

http://www.robotshop.com/media/files/pdf/rb-ite-12-

bluetooth_hc05.pdf

http://www.electronica60norte.com/mwfls/pdf/newBluetooth

.pdf

4. 8051 controlled Bluetooth transmitter circuit

https://www.pantechsolutions.net/media/k2/attachments/Int

erfacing_Bluetooth__With_8051.pdf

5. L6920D datasheet

http://www.st.com/web/en/resource/technical/document/dat

asheet/CD00002171.pdf

6. L3GD20H module description

https://www.pololu.com/product/2129

7. L3GD20H datasheet

https://www.pololu.com/file/download/L3GD20H.pdf?file_id=

0J731

8. Calculation of boost converter’s power stage

http://www.ti.com/lit/an/slva372c/slva372c.pdf

9. LSM303D module description

https://www.pololu.com/product/2127

10. Arduino and Java

http://playground.arduino.cc/Interfacing/Java

11. Battery datasheet

http://www.adafruit.com/datasheets/maxell_cr2032_datashee

t.pdf