Smart Solar Charger

Smart Solar Charger

Solar-powered lighting systems are now used in rural as well as urban areas. These systems include solar lanterns, solar home lighting systems, solar streetlights, solar garden lights, solar water heaters and solar power packs. All of them consist of four components: solar photovoltaic (PV) module, rechargeable battery, solar charge controller and load. The solar charge controller plays an important role as the system’s overall success depends mainly on it. It is considered as an indispensable link between the solar panel, battery and load.

Here we present the circuit of a highly efficient, automatic solar charger

based on PIC16F877A microcontroller. It shows the system status on an LCD and can trickle c

Fig. 1 shows the circuit of a microcontroller-based solar charger. In addition to microcontroller PIC16F877A (IC1), it uses regulator 7805 (IC2) and a few discrete components.

PIC16F877A is a powerful microcontroller that provides an ideal solution for hobby and industrial development. It controls battery charging through the solar panel. PIC microcontrollers use Harvard architecture.

Fig. 1: Circuit of PIC16F877A microcontroller-based solar charger

PIC16F877A is an 8-bit, high-performance RISC CPU with low power consumption. It has 8kB flash, 256 bytes of EEPROM, 368 bytes of RAM, 33 input/output (I/O) pins, 10-bit 8-channel analogue-to-digital converter (ADC), three timers, watchdog timer with its own on-chip R-C oscillator for reliable operation and synchronous I2C interface. The microcontroller can recognise and execute only 35 simple instructions. All the instructions are single-cycle, except branches which are two-cycle instructions.

Port pins RB0 through RB7 of the microcontroller are connected to data pins D0 through D7 of the LCD module, respectively. Port pins RD1, RD2 and RD3 are connected to RS (register-select), R/W (read/write) and E (enable) of the LCD, respectively. Preset VR3 is used for contrast control. Switch S1 is used for manual reset. A 4MHz crystal along with two 33pF capacitors provides basic clock frequency to the microcontroller.

Port pins RA0, RA1 and RA2 receive inputs to monitor battery voltage, charge current and solar panel voltage, respectively, to control the overall process and display information on the LCD module. When port pin RA3 goes high, transistor T1 becomes saturated and relay RL1 energises to connect the solar panel to the battery.

Regulator 7805 provides regulated 5V to the microcontroller and the LCD module. Fig. 2 shows the pin details of regulator 7805 and transistor BC548.

This solar charger can charge the battery in two modes—boost and trickle. If battery voltage is greater than 12V the battery is charged in trickle mode, whereas if battery voltage is less than 12V it is charged in boost mode. In trickle mode, the battery is charged at discharge rate.

The system also calculates the energy that has been received from the solar panel. This gives an indication of the power that can be harnessed from the Sun.

Construction and testing
An actual-size, single-side PCB for the PIC16F877A microcontroller-based solar charger is shown in Fig. 3 and its component layout in Fig. 4. Assemble the circuit on a PCB to minimise time and assembly errors. Carefully assemble the components and double-check for any overlooked error. Use IC base for microcontroller PIC16F877A. Before inserting the IC, check the supply voltage (5V) at test point TP1.

Fig. 3: An actual-size, single-side PCB for PIC16F877A microcontroller-based solar charger

Fig. 4: Component layout for the PCB

Fig. 5: Author’s prototype

Fig. 6: Flow-chart of the program

Before using the circuit, the system has to be calibrated for battery and solar voltages. This is done as follows:

Battery voltage. With battery disconnected, apply 20V at TP2 with respect to TP0. Use a multimeter to monitor the voltage at test point TP3 and adjust preset VR1 to get 5V. Check whether the voltage at TP6 is around 5V. Connect back the batteries. Now the voltage at TP3 should be around 3V.

Solar voltage. Remove the solar panel from the circuit. Connect a 12V battery at test point TP4 with respect to TP0 and monitor the voltage at test point TP5. Adjust preset VR2 to get 3V. Relay (RL1) enable can be checked at TP7.

The circuit is ready to harness the energy of the sun after calibrations. The power is calculated and displayed on the LCD in watts every second. The energy in watt-second is calculated by integrating the power.

Fig. 5 shows the working prototype of PIC16F877-based solar charger.

The following parameters are cyclically displayed on the LCD module:
1. Battery voltage in millivolts
2. Battery current in milliamperes
3. Energy in watt-seconds
4. Power in watts
5. Solar panel voltage in millivolts
6. Charger mode: boost or trickle

Download PCB and Component layout: click here

Download Source Code: click here

Software
The source program is written in Basic language and compiled using PIC Simulator IDE from Oshonsoft. The IDE provides a facility to program using Basic like commands, then compile the program and generate hex code. Burn the generated hex code into the microcontroller by using a suitable programmer.

The program works as per the flow-chart shown in Fig. 6. It starts by checking solar panel voltage. If solar panel voltage is more than 12.6 volts, the program moves to the next stage. If solar panel voltage is less than 12.6 volts, the program displays message “Low Solar Volts” on the LCD module and loops back to wait until solar panel voltage is above 12.6 volts.

If solar panel voltage is adequate, the system checks battery voltage and sets the charging mode to ‘boost’ or ‘trickle.’ A battery voltage of over 12V sets charging mode to ‘trickle,’ while a battery voltage of less than 12V sets it to ‘boost’ mode. During initialisation, the data is also read from the EEPROM, which stores the watt-hour readings. It gives an indication of the power absorbed from the sun.

The timer generates an interrupt every 65.56 ms. A 15-count in the interrupt service routine ensures that the energy and power are calculated every 65.56×15 =983.4 ms (almost 1 second).The power is integrated every second to get the energy in watt-seconds. The watt-hour readings are stored in the EEPROM of the microcontroller, so that the data is not lost due to power failure. To prevent too many write cycles in the EEPROM, the data is stored only every 30 minutes.

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BARCODE

Abstract

In 1948, a local food chain store owner approached Drexel Institute of Technology in Philadelphia asking about research into a method of automatically reading product information during checkout. Bernard Silver, a graduate student at Drexel Institute, along with fellow graduate student Norman Joseph Woodland, teamed together to develop a solution.

On October 20, 1949, Woodland and Silver succeeded in building a working prototype describing their invention as “article classification…through the medium of identifying patterns”. On October 7, 1952, they were granted a patent (US Patent #2,612,994) for their “Classifying Apparatus and Method”. Efforts to develop a working system accelerated in the 1960’s.

Bar coding was first used commercially in 1966, but to make the system acceptable to the industry as a whole there would have to be some sort of industry standard. By 1970, Logicon Inc. had developed the Universal Grocery Products Identification Code (UGPIC). The first company to produce barcode equipment for retail trade using (using UGPIC) was the American company Monarch Marking (1970), and for industrial use, the British company Plessey Telecommunications (1970).

In 1972, a committee was formed within the grocery industry to select a standard code to be used in the industry. IBM proposed a design, based upon the UGPIC work and similar to today’s UPC code. On April 3, 1973, the committee selected the UPC symbol (based on the IBM proposal) as the industry standard. George J. Laurer is considered the inventor of U.P.C. or Uniform Product Code

Introduction

A barcde is an optical machine-readable representation of data. Originally, barcodes represented data in the widths (lines) and the spacings of parallel lines, and may be referred to as linear or 1D (1 dimensional) barcodes.

They also come in patterns of squares, dots, hexagons and other geometric patterns within images termed 2D (2 dimensional) matrix codes. Although 2D systems use symbols other than bars, they are generally referred to as barcodes as well. Barcodes can be read by optical scanners called barcode readers, or scanned from an image by special software.

The primary barcode used in the United States is the UPC (Universal Product Code) barcode. The UPC is also the "original" barcode. The UPC was designed for the grocery industry. Because of the large number of items normally "checked-out" at the grocery store, a method was needed to speed up and eliminate "human" cashier errors. In 1973, the UPC barcode was born.

To the average person, the barcode looks confusing and complex, but to a "bar-coded" friendly computer, it's actually very simple

Bar Codes Basic

Bar codes provide a simple and inexpensive method of encoding text information that is easily read by inexpensive electronic readers. Bar coding also allows data to be collected rapidly and with extreme accuracy. A bar code consists of a series of parallel, adjacent bars and spaces. Predefined bar and space patterns are used to encode small strings of character data into a printed symbol.

Bar codes can be thought of as a printed type of the Morse code with narrow bars (and spaces) representing dots, and wide bars representing dashes.

A bar code reader decodes a bar code by scanning a light source across the bar code and measuring the intensity of light reflected back by the white spaces. The pattern of reflected light is detected with a photodiode which produces an electronic signal that exactly matches the printed bar code pattern. This signal is then decoded back to the original data by inexpensive electronic circuits.

Due to the design of most bar code it does not make any difference if you scan a bar code from right to left or from left to right.

The basic structure of a bar code consists of a leading and trailing quiet zone, a start pattern, one or more data characters, optionally one or two check characters and a stop pattern

There are a variety of different types of bar code encoding schemes, each of which were originally developed to full fill a specific need in a specific industry.

The different symbologies have different capabilities for encoding data. For example the UPC symbology used to identify retail products always contains 12 numeric digits.

These type of bar codes are called "linear symbologies" because they are made up of a series of lines of different widths. Most commercially available bar code scanners are able to read all of the different linear bar code symbologies therefore you do not need different readers for different types of bar codes.

New "2-Dimensional" bar code symbologies like EAN, Aztec Code etc. are also now available that can encode several thousand bytes of data in a single bar code symbol including text or binary data. The newer 2D bar code symbologies typically require special bar code readers that are designed specifically for reading them.

Bar Code Symbol Characteristics

1. Magnification

The magnification (size) of the bar code symbol is determined by the X-dimension (one narrow module width) in relation to a nominal size.

The allowable magnification range depends on the symbol type and the intended scanning environment. Reliability of scanning is always enhanced by selecting a magnification higher than the minimum.

To print an accurate and high quality bar code symbol a number of factors, such as the printing process, ink quality, and substrate, must be taken into consideration.

2. Bar Height

Once the magnification of the bar code symbol has been determined, for EAN/UPC Bar Code symbols it is important to ensure that the height remains in proportion to the magnification, and does not drop below the minimum specified.

3. Quiet Zones (Light Margins)

The Quiet Zones (Light Margin) of the bar code symbol are the solid, light areas before the first bar and after the last bar. These areas are extremely important as they allow the scanner to recognise the beginning and end of the bar code symbol.

Any obstruction or reduction in the Quiet Zones will most likely result in scanning difficulties.
The minimum size required for the Quiet Zones depends on the magnification of the bar code symbol.

It is recommended to allow slightly more than the minimum required Quiet Zones to allow for any possible ink spread or plate registration issues.

4. Colours

The colours and type of ink you choose for your bar code symbols is very important. As a scanner reads a bar code symbol using an infrared light source it sees the symbol differently to the human eye.

As a result, some colour combinations and ink types are unsuitable for scanning because they do not provide sufficient contrast between the dark bars and the light background, or they provide a much too high reflectance value.

The most suitable and reliable colour combination is black bars on a white background.
However, as a general rule, the background of the bar code symbol can be a light, warm colour that does not contain any black (such as yellow or light orange), and the bar colour can be a dark, cool colour that has no, or low, red content (such as dark blue or dark green).

5. Substrate

The substrate (the material the bar code symbol is printed on) is very important. If unsuitable this can cause scanning difficulties. Different packaging materials reflect light differently, which can have an effect on the scanning ability of the bar code symbol.

This is especially evident on transparent and translucent packages where the background is not printed.

For printing bar code symbols it is recommended that you avoid the following:

• High gloss substrates

• Transparent or semi-transparent backgrounds

• Transparent wrappers over the printed bar code symbol if necessary to print onto a highly reflective (flexible) substrate, we recommend the following:

• Increase the magnification of the bar code symbol to between 105% and 120% (X-dimension 0.35mm - 0.40mm)

• Increase the amount of Bar Width Reduction

• Make the background of the symbol as dense and less reflective as possible. To do this you may try the following:

• If you are not using wet inks, print two background layers. This may be two layers of the one colour, or you may use all light colours in the print run (e.g. white and yellow)

• Use a less viscous ink that will provide maximum coverage and density

6. Bar Widths and Print Quality

Always ensure that the print quality of the bar code symbol is of a high standard. Ensure that the bars in the symbol are clearly defined, watch for voids or smudging, and avoid flecks in the background colour.

Maintaining acceptable print quality and consistent print gain (ink spread) requires regular ongoing checks.

Anatomy of Barcodes

This number is a UPC system number that characterizes specific types of barcodes. In a UPC barcode it is normally on the left of the barcode. The actual "barcode" (the "bars" and "spaces") is the first "barcode" after the first "guard bar". The Number System Character is the blue box on the "Anatomy of a Barcode".

Codes of the Number System Character:

• 0 - Standard UPC number.
• 1 - Reserved.
• 2 - Random weight items like fruits, vegetables, and meats, etc.
• 3 - Pharmaceuticals
• 4 - In-store code for retailers.
• 5 - Coupons
• 6 - Standard UPC number.
• 7 - Standard UPC number.
• 8 - Reserved.
• 9 - Reserved

Conclusion and Future Scope

Barcodes — especially the UPC — have slowly become an essential part of modern civilization. Their use is widespread, and the technology behind barcodes is constantly improving. Some modern applications of barcodes include:

Almost every item purchased from a grocery store, department store, and mass merchandiser has a UPC barcode on it. This greatly helps in keeping track of a large number of items in a store and also reduces instances of shoplifting involving price tag swapping, although shoplifters can now print their own barcodes.

The tracking of item movement, including rental cars, airline luggage, nuclear waste, mail and parcels.

Entertainment event tickets can have barcodes that need to be validated before allowing the holder to enter sports arenas, cinemas, theatres, fairgrounds, transportation etc. This can allow the proprietor to identify duplicate or fraudulent tickets more easily

References

• Automating Management Information Systems: Barcode Engineering and Implementation – Harry E. Burke, Thomson Learning, ISBN 0-442-20712-3

• Automating Management Information Systems: Principles of Barcode Applications – Harry E. Burke, Thomson Learning, ISBN 0-442-20667-4

• The Bar Code Book – Roger C. Palmer, Helmers Publishing, ISBN 0-911261-09-5, 386 pages

• The Bar Code Manual – Eugene F. Brighan, Thompson Learning, ISBN 0-03-016173-8

• Handbook of Bar Coding Systems – Harry E. Burke, Van Nostrand Reinhold Company, ISBN 978-0-442-21430-2, 219 pages

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