31-12-2015, 03:50 PM
ABSTRACT
Color blindness or deficiency is the inability or decreased ability to see, or perceive color differences, under lighting conditions when color vision is not normally impaired. It may be a genetic disorder or an acquired one. Our Color Sensing System embarks upon enlightening the lives of the color blind by aiding them with accurate color identification. This system serves as a prototype for calibrating up to 16.7 million RGB color shades. The device is implemented using the RGB color sensor which uses the principle of Reflection of light to calibrate the RGB components of the color being viewed. This sensor has an in-built controller that helps in obtaining a digital value of the color thus preventing loss of data. This color value is fed to an ARM7 processor, which is pre-programmed to detect the exact color. Hence this color information is displayed along with an audio-playback to facilitate quick response. Thus the construction of this cost- efficient, full-fledged, feasible device shall prove to be a boon to the visually impaired. This system serves as a perfect asset for the color blind thereby enabling them to see and feel the world just like a normal human being.
INTRODUCTION
Color blindness occurs when there is a problem with the color-sensing granules or pigments in certain nerve cells of the eye called cones. There are three types of cone cells Red, Blue and Green cone cells that are found in the retina of the eye. Acquired color blindness may be due to ageing, eye problems such as glaucoma, cataracts or diabetic retinopathy, injury to the eye and side effects of some medicines. There are three types of inherited or congenital color vision deficiencies: Monochromacy (absence of all three cone pigments), Dichromacy (one of the three cone pigments is missing or not functioning) , and Anomalous Trichromacy (one of the three cone pigments is altered).
Medical cure is not the best option for color blindness because surgery has side effects like irritation, infection, retinal damage and at times the person becomes completely blind. Gene therapy can also serve as a method for cure but Scientists are still working on this. Hence the Field of Medicine fails to provide a complete solution for the problem. Because of this, people with color blindness may not be able to get a job that requires the ability to see colors accurately. For example, electricians (color-coded wires), painters, fashion designers (fabrics), and cooks need to be able to see colors accurately. So our system serves as a perfect asset for the color blind thereby enabling them to see and feel the world just like a normal human being.
SYSTEM ARCHITECTURE
The hardware structure is mainly dominated by three units, namely the color sensor; ARM Processor and an Audio cum Visual interface, followed by other components.A color sensor is a device that senses different shades of colors. This system uses the RGB color sensor that is capable of identifying up to 16.7 million color shades, thus giving a serial RGB value for the detected color. The detected color is identified as amount of three primary color values namely Red, Green & Blue with 8 bit accuracy for each primary color. Any color can be separated or combined into three primary colors Red, Green and Blue using the RBG values.
The operation of this RGB color sensor is based on the principles of Reflection and Induction. By the principle of Reflection of light, the color sensor contains a multicolor LED emitter from which the light is emitted on to the surface. The sensor switches each primary color RGB, one by one and checks what intensity of color is reflected by the surface of detection. This reflected intensity is absorbed by the cadmium-sulphide photocell. The amount of red light, green light, and blue light is measured, each component is individually scaled based on minimum and maximum values obtained at calibration and is converted to 8bit value. The measured color component values are assembled together to form a single color.
According to the Induction principle of the three primary colors which create various other colors in nature, once the value of three primary colors is confirmed, the color of the tested object is known. Knowing the value of RGB helps people gain the color of the light which is projected onto the sensor since each color corresponds to only one value of RGB.
The output is in the form of serial data at 9600 baud rate consisting of 19 bytes for each 500ms interval. When RED shade of color is detected we would get following type of data in the terminal R=130 G=030 B=030. Here value of RED is 130 while Green and Blue are 30 both. Each value will be from 0 to 255.
The output of the color sensor is initially in the form of analog serial RGB voltage values. In order to facilitate further calibration, we use an inbuilt PIC 12F675 microcontroller, which gives digital RGB output. This 8-pin PDIP controller comprises of an analog to digital converter module with 10 bit resolution. The analog-to-digital converter (A/D) allows conversion of an analog input signal to a 10-bit binary representation of that signal. The PIC12F675 has four analog inputs, multiplexed into one sample and hold circuit. The output of the sample and hold is connected to the input of the converter. The converter generates a binary result via successive approximation and stores the result in a 10-bit register.
The color sensor data output is read to the microcontroller using the TTL UART interface. In general, different devices operate under different voltage ranges. So this transistor-transistor logic (TTL) acts as a buffer, thus tolerating the voltage differences. The TTL is made up of bipolar transistors. We use IC 74HC245, a high-speed Si-gate CMOS device that possess low power consumption and high noise immunity. The logical signals of 0 and 1 are usually represented by voltage levels having typical nominal values of 0V and +5V. In our system, this is basically used as a 3V to 5V converter, thereby interfacing the data from color sensor to the microcontroller.
In our color sensing system,the ARM embedded system acts as a central processing unit, thereby having a critical influence on the overall performance. So we use the LPC 2148 microcontroller which is based on a 32-bit ARM7TDMI-S CPU in a tiny LQFP64 package, supporting real-time emulation. It is noted for its high performance and very low power consumption. The LPC2148 contains two UARTs namely UART0 and UART1. In our system, the hex code values for each color are pre-programmed and the code is loaded to the microcontroller through the UART0. Similarly, the data from the color sensor is interfaced through the UART1 of the controller using the TTL. So, as soon as the color sensor sends the calibrated digital RGB value, the microcontroller performs comparison of the values obtained against the pre-programmed color chart. Consequently, it matches the exact color word which in turn is communicated to the user in an audio visual format.
UART Data Format
In the present work, we have implemented the designed color sensing system to sense the basic color shades. This however is only a prototype for identifying up to 16.7 million color shades. In order to achieve this target, our system incorporates the training mode, in addition to the above explained normal mode, wherein we use an EEPROM.
The AT24C64 provides 65,536 bits of serial electrically erasable and programmable read only memory (EEPROM) organized as 8192 words of 8 bits each. The device switches to the training mode once a new color value is detected for the very first time. This gets stored in the EEPROM and in the meantime, the color word can be entered by connecting a keyboard to the PS2 connector of the microcontroller. Thus the kit can be trained in this manner for detecting any number of colors.
A bidirectional flow is established between AT24C64 and LPC2148 by using an Inter-Integrated Circuit(I²C). It is a multi-master serial single-ended computer bus. We use the fast-mode I²C bus which operates at a high speed of 400kbps. It is referred to as the "two-wire interface" as it requires only two bus lines for transmission namely the SCL and the SDA lines.
The processed color information is now made available to the user through a compact liquid crystal display (LCD). The 2 x 16 flat panel alphanumeric LCD display is an 8 bit parallel interfaced LCD, that uses the light modulating properties of liquid crystals. A 2x16 LCD can display 16 characters per line and there are 2 such lines, one displaying the color name and the other line displaying the color value. In this LCD, each character is displayed in 5x7 pixel matrix.
The LCD has two registers, namely, Command and Data. The command register stores the command instructions given to the LCD. A command is an instruction given to LCD to do a predefined task like initializing it, clearing its screen, setting the cursor position, controlling display etc. The data register stores the data to be displayed on the LCD. The data is the ASCII value of the character to be displayed on the LCD. The LCD modules are preferred over seven segments and other multi segment LEDs as they are economical; easily programmable; consume low power; have no limitation of displaying special & even custom characters.
Block Diagram of Audio Chip
In order to make this device a user-friendly one, we incorporate the audio playback feature. The inclusion of an effective low power reprogrammable voice chip guides the color blind and facilitates quick response. Here, we use IC aP89341, a 24-pin DIP 300 MIL package, which is a high performance Voice OTP, fabricated with Standard CMOS process and an embedded EPROM of 8Mbits. It can store upto341seconds of voice message with 4-bit ADPCM compression at 6KHz sampling rate.
Voice files created by the PC base developing systems are restored in the built-in EPROM of the aP89341chip as a number of fixed length Voice Blocks. Voice Blocks are then selected and grouped into Voice Groups for playback. Up to 254 Voice Groups are allowed. Voice blocks can be combined to extend playback duration. Voice data stored as 4-bit ADPCM provides 2:1 data compression which can save 50% of memory space. The desired voice group can be enabled by providing trigger pulses from the micro controller. Built-in resistor controlled oscillator, 8bit current mode D/A output and PWM direct speaker driving output minimize the number of external components. Now the analog voice output can be amplified with a gain factor of 200.
HARDWARE MODULE
A. ARM 7 PROCESSOR
ARM is a high performance, power efficient RISC processor. The LPC2148 microcontroller is based on a 32bit ARM7TDMI-S CPU which is a tiny LQFP64 package with 40 KB on-chip static RAM and 512 KB of on-chip flash program memory. 128-bit wide interface/accelerator enables high-speed 60 MHz operation. Single flash sector can erase the chip in 400 ms and programming of 256 bytes in 1 ms. Up to 45 fast general purpose I/O pins are available that can tolerate a voltage of 5V. Multiple serial interfaces includes two UARTs (16C550) and two fast I2C-bus (400 Kbit/s).
B. COLOR SENSOR
A color sensor is a device that senses different shades of colors. It works on the Principle Of Reflection of light and uses the Induction Principle for identifying the Red, Blue and Green color values. It operates at 5V and provides a simple serial data output. The color sensor has an in-built PIC microcontroller which is a high performance RISC CPU. It is a power saving microcontroller and has high endurance with a UART interface for direct connection to any MCU or USB-TTL convertor. There is an analog to digital converter module with 10 bit resolution.
C. AUDIO DEVICE
aP89341 is a high performance Voice OTP, fabricated using standard CMOS process with an embedded EEPROM of 8M bits. It comes as a 24-pin DIP 300 MIL package. It can store up to 341 seconds of voice message with 4-bit ADPCM compression at 6KHz sampling rate and can occupy a maximum of 254 voice groups. 7680 table entries are available for voice block combinations. Three triggering modes are available. Built-in resistor controlled oscillator, 8-bit current mode D/A output and PWM direct speaker driving output minimize the number of external components.
D. LCD DISPLAY
A liquid crystal display (LCD) is a flat panel electronic visual display, that uses the light modulating properties of liquid crystals. Its low electrical power consumption enables it to be used in battery-powered electronic equipment. The 2 x16 Parallel LCD is an 8 bit or 4 bit parallel interfaced LCD. This unit allows the user to display text, numerical data and custom created characters. It is operated at a 5V power supply.
E. EEPROM
EEPROM (Electrically Erasable Programmable Read-Only Memory) is a type of non-volatile memory used in computers and other electronic devices to store small amounts of data that must be saved when power is removed. We use the highly reliable AT24C64 that provides 65,536 bits of serial electrically erasable and programmable read only memory organized as 8192 words of 8 bits each. The device’s cascadable feature allows up to 8 devices to share a common 2-wire bus where low power and low voltage operation are essential.
F. I2C
I²C (Inter-Integrated Circuit) is referred to as "two-wire interface" which is a multi-master single-ended computer bus. A serial 8-bit oriented bidirectional data transfer is possible with the help of this bus. It involves collision detection and arbitration to prevent data corruption when two or more masters simultaneously initiate data transfer. It is used to attach low-speed peripherals to a motherboard/embedded system. The original communication speed is defined with a maximum of 3.4 Mbit per second. But here we are using a fast I2C bus whose speed is 400 Kbps. Simple master/slave relationships exist between all components. Each device connected to the bus is software-addressable by a unique address. Only two bus lines are required: a serial data line (SDA) and a serial clock line (SCL).
G. TTL LOGIC
TTL Logic is Transistor – Transistor Logic which is based on bipolar transistors. It is the most popularly and widely used IC logic family with a standardized labeling system. This device employs transistors with multiple emitters in gates having more than one input. Transistors are active devices that tend to restore signal levels and preclude signal deterioration which could cause 1 and 0 indistinguishable. This device is operated at +5V supply and has a noise immunity of 1 to 1.6V. It provides greater flexibility with regards to speed and power dissipation.
CONCLUSION
Thus we have designed and implemented a flexible, high speed prototype of an ideal color sensing system which will serve its purpose as the third eye to the color blind. It not only gives the color value but also provides the exact color name thereby serving as a perfect aid for the people with color vision deficiency. This system can respond rapidly and has a friendly user interface including a LCD and an audio-playback device. Further extension of this system can be executed by integrating with newer technologies that would enable us to achieve far greater improvements in this area of concern. This would pave way to far reaching consequences in the biomedical embedded field.