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Safe Current Appliance Guard Safe Current Appliance Guard is useful to protect your electrical / electronics equipment / appliance / gadget from over current flow through them. The circuit can display current flow value and guard both AC and DC appliances, when the current flow them exceeds more than trip value set by you. ATTINY84 is used for the project, which is the heart of the circuit to read the current value and trip the relay in case the current flow is more than trip value, for more than one second, which is set by the user. The ADC system of the ATTINY84, continuously reads the voltage (or signal) generated by ACS 712 (hall effect) current sensor. Then the ADC value is multiplied with ACS_MF, and displays as READ CURRENT on the OLED. Before reading AC or DC current flow, the RELAY is switched ON through a transistor. Then, the ADC value is read 25 times continuously with one milli-second interval and records the peak ADC value (out of 25 samples), so that peak value of at least one full wave can be read for 50 Hz or 60Hz AC current. If the peak values, thus read, is exceeding more than three times consecutively (approximately 1.3 seconds), then the ATTINY84 switches off the relay (through transistor). ​ The full circuit diagram is available below: INITIAL SETUP: ​ Once the circuit is ready on general purpose (vero board is preferred) PCB, connect DC power supply (9V battery), then connect AVR programmer to ISP port of ATTINY84 and write/burn SafeCurrentGuard.HEX file to the micro controller. The program displays the title of the project, then displays the READ CURRENT and TRIP CURRENT values on the OLED. To set TRIP value, press SW_UP or SW_DN button. Then the OLED displays the existing Trip value. Now, you may press SW_UP or SW_DN button to increase or decrease the Trip value respectively. If, no input is found from the SW_UP or SW_DN buttons for more than 5 seconds, then the displayed value (new value) is saved to EEPROM and the Trip value is available after switch off the circuit also. ​ To calibrate the READ CURRENT value, connect an DC Ammeter or multi-meter, in current mode (10A or more), in series as shown here. Now, Restart the circuit and observe the difference in READ CURRENT value and multi-meter value in amperes. If, the value is different, then note down the percentage of error. Now, press SW_RST to restart the circuit. While displaying the Title of the project on OLED, press and hold SW_UP or SW_DN button until the current multiplication factor is displayed on the OLED screen. Now, adjust the displayed value to suit the error percentage noted earlier. Increase the multiplication value, if the READ CURRENT is low and vice-versa. The value will be saved to EEPROM, once no button is pressed for more than 5 seconds. Now, compare the READ CURRENT w.r.t. to multi-meter value and adjust the multiplication factor, till the READ CURRENT matches to the multi-meter value. Once calibrated, remove the multi-meter and reset the circuit as shown above. Now, your circuit is ready to use. If, you have no need to change the values, i.e., once calibrated and trip current value is set, then the OLED, SW_UP and SW_DN buttons may be permanently disconnected (or removed). WORKING: ​ Once calibrated and set the trip current value, then connect the actual load, in series as shown in the circuit. Then, power-on the circuit, using any conventional 12VDC power supply (using transformer) or 12VDC SMPS. The Title is displayed on OLED, then Relay is set to ON mode and continuously displays the current flow through the load, which is indicated by slow blinking of LED2 . If, at any time, the current flowing through the load exceeds the set trip value for more than one second, then the relay is set to OFF mode, the trp message is displayed and the LED2 blinks quickly. ​ You may press SW_RST to restart / reset the circuit. The LED1 indicates the presence of DC power supply. The LED3 is complementary (opposite state) to relay status. You may use this output to generate alarm using piezo-buzzer etc. ​ ​ Use shorting jumper in J1 mode, if the relay is operating on 5V and the input DC power supply may be 8VDC to 12VDC. Set in J2 mode, if the relay selected is operating on 12V and input DC power supply should be 12VDC. The current sensor ACS-712 is normally available in 5A or 20A or 30A capacities. Select the capacity/module as per the load requirement. The thick line shown in the circuit should carry the flowing current through the load. The multiplication factor depends on the capacity of ACS-712, which can be adjusted using the SW_UP and SW_DN as explained in calibration method. ​ The theoretical value of multiplication factor for 5A module is 264, for 20A module is 488 and for 30A module is 740. click the link / attachment to download the file and rename as SafeCurrentGuard.HEX , then upload to ATTINY84 using any suitable AVR programmer. SafeCurrentGuard.HEX For source code (in C-language), (SafeCurrentGuard.C) please send message through contact form . The code will be sent to your e-mail.

HARDWARE PAGE

microcontroller - an INTRODUCTION Micro-Controller or Micro-controller Unit, (MCU in short) may be assumed as a miniature CPU box of a PC packed in an IC (Integrated Circuit). The MCU mainly consist of Clock generation and control system, ALU (Arthmatic and Logic Unit), Registers / Accumulators, RAM (Random Access Memory), Program Storage Memory ( Flash Memory ), Input and Output Control system, Communication system etc. ​ The following parameters / Specification in combination are important for selection of an MCU: Number of Bits ( 8 or 32 etc. ) Storage Memory ( or Flash Memory ), in Kilo Bytes SRAM (Static Random Access Memory), in Kilo Bytes Clock Speed , in Mega Hertz Number of IO (Input/Output) pins EEPROM (Electrically Erasable Programmable Read Only Memory ) Timers and Counters ADC (Analog to Digital Converter) channels Types of Serial Communications (USART, SPI, TWI, USB etc.) Interrupt management system Memory Programming and Life cycles Operating Voltage and Power requirements. Working Temperature Range. Price, Availability, Package and matching to the requirement. Programmer Availability Easiness of Software development ( programming and IDE ) ​ Some MCUs may have all or some of the the above parameters, and some may have more than the above mentioned in the list As per the block diagram of Microcontroller Architecture, a clock will control all the operations inside the MCU. So, higher the speed of clock, quicker the operations performed by the MCU. Most of the MCUs have calibrated internal clock option as well as external clock input. ​ The ROM is the actual storage space for the program to stay in the MCU. The clock will control the fetch and execute operations sequentially as per the program. A read / write control system is used, while programming the ROM ( Flash memory ) and EEPROM. EEPROM may be written directly or through the program written in the Flash memory. ​ The Digital, Analog, Serial Input/Output are controlled by the program loaded in the flash memory. ​ The ALU, SRAM, Interrupts are controlled by hardware and software ( program in flash memory) automatically. So, all the blocks in the MCU have clock and data bus connections and have control through the program loaded in the Flash memory. So, a software (program) is required to control all the blocks as per the individual's requirements. ​ A 32 bit MCU is faster ( costlier also ) than 8 bit MCU. Similarly, higher the Storage Memory capacity , SRAM and Clock Speed have advantage while processing complex program also also attracts more cost. Selection of MCU also depends on the IO pins and communication system availability. So, balancing should be done with the requirements and the cost of the MCU.

About . . . Simple mechatronics wishes a Good Day to you. ​ Are you an electronics hobbyist? Are you interested in self-learning of electronics? Are you novice in electronics and want know about electronics? Are you a teacher and make your kids know basics of electronics? Are you an electronics student? Are you curious in practical knowledge in electronics? Are you interested in Mechatronics? Are you interested in simple electronics projects? Are you interested to know about micro-controllers? Are you interested in micro-controller projects? Are you interested in Robotics? Are you searching for a circuit diagram? Do you want to learn electronics with practical knowledge? Do you want an idea for your acadamic project? Do you want to learn basics about computers? Do you want to learn computer languages? ​ If your answer is YES to at least any one of the above questions, then, this blog suits for you. ​ The main aim of this blog is self-learning of electronics, mechatronics step-by-step, from basics to practical knowledge and Make-at-Home Projects. ​ Home page contains the list of contents and same is available through the menu. ​ You may SEARCH a topic using a keyword or phrase through the search option available above the menu. ​ -: ALL THE BEST to you :-

displays Displays are used to show the output of a process or status of equipment or monitoring the status of the process. LEDs: The simplest display used in an electronic equipment is two lead LED , one for anode(+ve) and another for cathode(-ve). The LED indicator is simplest and cheapest display system for monitoring the process, available in multiple colours, which makes the display of status more easier. The LEDs works between 1.8 VDC to 3.5VDC, which depends on emitting colour and manufacturer . The current capacity depends on its size (in diameter) and wattage. for more description on LEDs click here Seven Segment LED Displays: Next comes the Seven Segment Display, which is a rectangular block having seven long rectangular LEDs in 8 format. The Seven segment display is normally used to show numerics from 0 to 9 by switching ON and OFF particular LEDs. Sometimes some Alphabet are also displayed using Seven Segment Display. Connecting pins for each LED (segment) are available at the back side of the Seven Segment Display, with one or two common pins for all seven segments. The common pin may be connected to positive (or negative) DC power supply and other pins of seven segments may be connected to negative (or positive). For Common Anode (CA) Seven Segment Display, the common pin(s) should be connected to Positive DC power supply and each segment pin should be connected to negative power supply to glow the particular segment (or LED). Similarly, for Common Cathode (CC) Seven Segment Display, the common pin(s) should be connected to Negative DC power supply and each segment pin should be connected to positive power supply to glow the particular segment (or LED). In general, Seven Segment Displays may glow in Red or Green colour in various sizes like 0.5", 1", 2.5", 4" etc. Now-a-days Seven Segment Displays are available in RGB colours also. All the Seven Segments are named as a, b, c, d, e, f, g and one more pin is used to glow dot on the right bottom side of the rectangle. The pin connections depends on the model , size and manufacturer. Connections and identification of seven segment are shown here for Seven Segment Display with top and bottom pins. The seven segment displays are also available in multiple displays in one block. This will reduce the wiring and number of pins to control the display. For continuous display, each segment of particular display has to be selected sequentially, which may be managed by a micro-controller. ​ A 4-in-1 seven segment block is shown here. similarly, 2-in-1 and 3-in-1 are also available. Sixteen Segment Alpha-Numeric LED Display: The 16 Segment LED display is similar to Seven Segment Display, except it can display all Alphabets and Numerics. ​ The main difference is, the three horizontal segments ( a, g and d ) are made in two parts , two vertical and four inclined segments are added in between. LED Bar Graph: LED Bar Graph is a rectangular block with 10 number of LEDs arranged in a row. The connecting pins (10 anode + 10 cathode) are available at the back side of the block as shown in the figure. They are available in Red or Green or Blue or Yellow or Amber or R G B colored LEDs LED Matrix Array: 64 LEDs are arranged in 8 X 8 matrix format in a square block. By selecting pins at the back side of the block, required LEDs in combination of 8 rows and 8 columns may glow. ​ The LEDs may glow in Red or Green or Blue colour. Now-a-days, RGB colours are also available. In this case, each LED may glow in combination of colours. So, the LED matrix is very useful to display pictures or graphical output. ​ It is very difficult to select each LED out of 64 LEDs. So a separate display controller IC (MAX7219) is used for the purpose. The IC has serial data input and serial data output pins, which may controlled by a micro-controller. ​ A display module with the IC (MAX7219) is readily available in the market. Some modules have two or four display blocks on single PCB and simple serial data control system. Any number of LED matrix modules may be connected in series and are to be controlled by a micro-controller (or similar circuit). ​ A readily available 4-in-1 LED matrix module is shown here, which has input pins one side and output pins on another side to connect further / next modules in series. LCDs: The LCD (Liquid Crystal Display) is highly used text display in micro-controller projects, which is cheaper and easily available. The text may be displayed in the following ranges: ​ 1 Row x 16 Columns 2 Rows x 16 Columns 4 Rows x 16 Columns 4 Rows x 20 Columns ​ The LCD may controlled by 16 pins. The data may be sent by 8 bit (byte) or 4 bit (nibble), which should be selected by sending specific codes after power on. The contrast of the display is controlled at pin-3 of LCD, through a trim-pot connected between 5VDC and ground. GLCDs: The GLCD (Graphical Liquid Crystal Display) has good viewing size of pixel size (0.48mm x 0.48 mm) and screen area (66mm X33mm approx.). The screen is logically divided into two panes as 64X64 pixels on left side and 64X64 pixels on right side, which makes 128X64 pixels in total. The left side pane is selected using CS1 pin and similarly right side pane is selected using CS2 pin. The data and command to GLCD is transmitted in 8 bit format by selecting RS pin setting high/low. The contrast of the display is controlled at pin-3 of GLCD, through a trim-pot connected between -10VDC ( available at pin 18 of GLCD) and ground. OLEDs: OLED ( Organic Light Emitting Diode ) is available in very small size with graphical display support, which consumes very less power and displays sharp image. ​ The input pins contains either I2C (TWI) or SPI (or both) interface with two power supply pins. The display size and display colour(s) varies as per specification. The OLED shown here are highly used in the DIY projects. TFT Displays: TFT-LCD (Thin Film Transistor Liquid Crystal Display) has smaller and sharper pixel than normal LCD display and consumes lesser power. TFT-LCD can display an image or text in colour. Some TFT-LCD modules have touch sensitivity with stylus and/or Micro-SD card slot. Most of the small size (upto 3.5 inch) TFT-LCD modules have pins, which are compatible (suitable) for Arduino Uno / Arduino Meaga boards. The higher sized TFT-LCD modules may have various signal input pins and slots like, USB, VGA, HDMI etc. Other display systems like AMOLED (Active-Matrix Organic Light-Emitting Diode), SAMOLED (Super Active-Matrix Organic Light-Emitting Diode), QLED (Quantum dot Light Emitting Diode) are new technologies emerging in the market. But, proper interfacing system for DIY is not available right now. In future, some more new technologies in display system is expected with high quality and low power consumption at affordable price.

Resistors: As the name indicates, Resistor reduces flow of current in a circuit. Resistor is highly used element in electronic circuit. The value of a resistor is called Resistance and its units are (i.e. measured in) Ohms. The symbol for Ohms is omega ( Ω ). The property of the material which exerts resistance is called resistivity and its units are rho ( ρ ). Fixed Value Resistors: The value of resistance cannot be modified in a circuit is Fixed Resistor. These resistors are made of mixture of mainly carbon and part of ceramics to attain the required resistance value. The surface is coated with resin and colour bands are marked on its surface to indicate its resistance value in case of small size resistors. For big size resistors, the resistance value , tolerance and power is printed on the surface of the resistor. For higher power and lower resistance requirements wire wound (a wire is wound on a hollow insulating shell and coated with resin) resistors are used. ​ Standard Resistance values available in multiples of 1.0 / 1.2 / 1.5 / 2.2 / 3.3 / 4.7 / 5.6 / 6.8 / 8.1 ohms. ​ Normally Resistor are available in following Wattages 0.25W / 0.5W / 1W / 2W / 5W / 10W and so…on. The value of resistance on fixed resistor is marked using colour bands on its surface in a coded form. The first and second colour bands indicates two digits sequentially with respective colour code, the third colour band is the number power to 10 for that colour and the forth colour band indicates tolerance value, i.e., maximum + / – deviation of resistance value. Variable Resistors: As the fixed resistors have tolerances, which makes the user cannot totally depend on the exact resistance value of the fixed resistor. Variable resistor is useful when the resistance is to be adjusted to suit the circuit requirement. ​ Variable resistor generally have 3 connections, two connections for extremes of carbon resistance and one connection is connected to moving arm, which moves on the carbon resistance for adjustment. ​ Small size variable resistors which are used to be fixed on the PCB and adjusted rarely are called Trimpot. The bigger size variable resistor, which is frequently used to vary the resistance and have knob fit on to it is called Potentiometer . OHM's Law -vs- Resistors: In simple terms, Ohm's law states that the voltage across a resistor is directly proportional to the current flowing through the resistance. So, as per Ohm’s law, V or I or R are inter-connected and each value can be calculated, if other values are known. Assuming the Voltage is fixed for a circuit, in general, by increasing resistance, the current flowing through the resistacne will decrease and vice-versa. ​ Once the V, I and R are calculated, then the power (W) requirement of Resistor is to be calculated. If the resistor wattage is less than the calculated value, then either resistor will get over-heated or damaged. Resistors in SERIES Connection: If multiple resistors are used in series in electronic circuits, the resultant resistance is equal to sum of each resistance in the circuit. So, the Resultant Resistance is always more than any resistance in series connection in the circuit. Resistors in PARALLEL Connection: If multiple resistors are connected in parallel in a circuit, the inverse resultant resistance is equal to sum of inverse resistance of each resistor in parallel. The Resultant Resistance is always less than any resistance value of any resistor in the parallel connection in the circuit. Adding resistor parallel to existing resistor reduces overall resistance and increases total current flowing through both the resistors MORE RESISTANCE CONNECTIONS ARE AVAILABLE IN RLC CIRCUITS (FUTURE USE)

BASIC TOOLS The tools necessary for Make-at-Home projects are listed below with comment as Basic or Important or Optional keyword, which means that, BASIC : very much required and affordable IMPORTANT : having this tool is advantageous OPTIONAL : may be purchased later SCREW DRIVER : The necessary basic tool is Screw Driver, which is used to open or close any fittings. The screw driver is also necessary for fixing some components on the PCB (Printed Circuit Board) of the Make-at-Home projects. A good quality screw driver have good and convenient grip, which is useful to have more torque to open / close the screws. (BASIC) SCREW DRIVER SET : The basic screw driver is useful to open/close screws with a line slot on screw's head. But, the screw heads may have different grip shapes on their head. So, a screw driver set, with different screw driver tips, which are changeable to match the type of screw head, is more useful. (IMPORTANT) The above screw driver set may be used to open / close straight (minus) or start (plus) slotted headed screws. Some times, you may come across special slotted screw head shapes like, five / six edged star, with various sizes. In that case, a special screw driver set shown here may be useful. But, the requirement of this screw drirever set is very less for the projects available in Simple Mechatronics. (OPTIONAL) CUTTING PLIER & NOSE PLIER : The Pliers are useful hold, open or close bolts, nuts , cut wires (copper, aluminum, GI) etc. The pliers are useful for fixing of some electronic equipment, like transformers, which uses hexagonal or square headed screws and nuts. Pliers are useful to cut some wires also. The nose-plier is useful to hold small size bolts and nuts, in narrow spaces, inside the cabinet. (IMPORTANT) WIRE CUTTER AND WIRE STRIPPER : Many times you may require to remove the shield on the wire, or cut the wire to desired length. So, a wire cutter or wire stripper is very much useful. There is some adjustments on the wire cutter / wire stripper to adjust the gap for removing the shield on the wire, without damaging the metal wire inside. Any one type of the following wire cutter-cum-stripper shown below may be required. (IMPORTANT) SLIDING CUTTER / KNIFE : The sliding knife, shown here, is useful to cut papers, card-boards, foam sheets, rubber products and very important is PCBs to required sizes. The main advantages with this type of cutter/knife are 1) the blades are changeable, which are available at affordable price. 2) the cutting edge may be pushed out, whenever required only, which is safe while not working with it. (BASIC) HAND DRILL FOR PCB : The Hand drill does not require any electrical power and very useful tool to make holes on the PCB. Some times, a few holes on some PCBs are not drilled properly or the hole size may not be sufficient to insert the lead of the the component. In such cases, the hand drill is very comfortable to make or expand hole(s), wherever is required on the PCB. (IMPORTNANT) NAIL CUTTER : You may be surprised to see a nail cutter as a tool. But, it is useful to cut the free leads of components (like resistors, capacitors etc) after soldering on PCB. Some times, it is more convenient to cut the extra leads, behind the PCB, compared to wire cutters. (BASIC) SCISSORS : The scissoris are useful to cut thin and thick papers, generally used for labels and base sheets. The scissors are also useful to shear/cut very thin metal sheets made of copper / G.I. sheets. The thin sheets are used to make cabinets for project. (OPTIONAL) MAGNIFYING GLASS : A magnifying glass (convex lens) is useful to read the small details, printed on electronic components, which are difficult to read with naked eys. Magnifying glass is somtimes useful to know any soldering defects also (IMPORTANT) ​ SPANNERS (WRENCH) : The spanners are used to open / close hexagonal / square headed bolts / screws / nuts. The open ended spanners and ring spanners are used for specific size, which are marked near the opening or ring shape. (OPTIONAL) Where as, an adjustable spanner can adjust the gap between its jaws, by rotating a roller shaped worm, so that , it can hold various sizes of bolts and nuts. (IMPORTNANT) ALLEN KEY : The Allen key is used to open / close hexagonal socket headed screws. These screws are rarely used in electronic equipment. Some times motors and other hardware items are clamped using these type of screws / bolts. These type of small screws may be opened / closed using special screw driver set shown earlier. (OPTIONAL) HACK SAW : Hack saw is useful cutting tool, while making cabinets, using sheet metal, plastic sheets, wooden items, PVC pipes etc. The main advantage of hack saw is, removable blade. The hack saw blade is easily changeable and easily available at affordable price. (IMPORTNANT) ​ A bench vice is preferred for proper holding of the component, while cutting it, with hack saw. (OPTIONAL) WOOD SAW : The Wood saw is also useful tool to cut wooden or hi-lam items for making base of the circuits and containers. Little experience is required for proper cutting of wooden items in straight line. (OPTIONAL) HAMMER : A hammer is also useful tool while flateninig sheet metals, making cabinets etc. The hammer shown in the image is Claw Hammer, which has slotted end on other side to remove nails etc., from wood. (OPTIONAL) FILE(S) : A (mechanical) file is used to remove material (especially for metals) by abrasion method. A file is useful tool to cut and shape a hole or ends of metallic or wooden parts or PCBs etc. Wood files are especially used for shaping wooden items. The files used for metal and wood are available with various cross-sections to suit the requirement, like rectangular, square, triangular, circular, semi-circular etc. (OPTIONAL) GRINDING STONE : A cuboid shaped grinding stone is useful to clear the burrs of PCB after cutting to required size. It is also useful to sharpen the cutting edges of scissors, cutting blades etc. (OPTIONAL) Never expect FRUITS from the today's plantation. – Simple Mechatronics

Soft Starter + Soft Stopper Some AC / DC motors and Universal motors has to connect to mains power supply smoothly. For high current flow motors, the mechanical switches or relays create sparks, while connecting and disconnecting to the mains. So, the circuit explained here, connects to power supply by slowly increasing to mains supply and disconnects from the power supply also slowly decreasing. The project is divided into two parts for easy understanding and making of the circuit. 1) Power Board Circuit using BTA41A-600B Triac. DB3 Diac, LDR etc. 2) Control Board Circuit using DB107 Bridge Rectifier, 12V zener diode, LEDs, Capacitor etc. POWER BOARD: BTA41-600B TRIAC is used to control the power supply to the motor through DB3 DIAC. An LDR (Light Depending Resistor) is connected in series with 180K resistance and two numbers of 0.1uF capacitors. By varying the light falling on the LDR, the power of the motor (or Load) can be controlled. ​ A single 0.22uF capacitor may be used instead of two numbers of 0.1uF capacitors shown in the circuit. ​ Proper wire (by cross section and insulation) should be used for load, as shown in thick line in the circuit diagram. ​ Refer Power Board circuit diagram: CONTROL BOARD: The AC mains supply is converted to DC using Bridge Rectifier (DB107) and Zener Diode regulates to 12VDC, through the series resistance 220K. When the SPDT switch is connected to ON position, the 470uF capacitor starts charging and both the LEDs (Red and White) starts glowing slowly. Similarly, when the SPDT switch is pushed to OFF position, the same charge in 470uF capacitor starts discharging and both the LEDs goes to OFF mode slowly. ​ The ON time delay may be changed by adjusting VR1 (20k) and OFF time delay may be changed by adjusting VR2 (20K). ​ The delay for Start time may be further increased by increasing the series resistance 220K (up to 470K). ​ Refer Control Board circuit diagram: CONNECTING THE BOARDS: Both the circuit boards are to be connected to single circuit for proper working of Soft Starting and Soft Stopping of the motor. The White LED of the control board and LDR of power board are to be concealed in a plastic tube with little gap. As the brightness of white LED increases (which may be visualized by outside Red LED), the resistance of LDR decreases and more power is transmitted through the BTA41 triac. Adding a semi-transparent sheet in between them, like a curtain, is added advantage, which will allow controlled lighting from LED to LDR for more precision control. ​ Refer Full circuit diagram: CAUTION: 1) Basic Electrical wiring knowledge is mandatory for making and testing this project. 2) Circuit should not be touched, while mains power is ON. ​

Stepped Desktop Power Supply Most of the times a fixed voltage power supply is very much required for quickly connect and test an electronic equipment. Having bi-polar (both positive and negative) DC power supply is added advantage for working with op-amp circuits etc. The circuit of Stepped Desktop Power Supply is simple and easy to construct. The input should be in between -18VDC to -21VDC for negative output voltage power supplies -3VDC, -5VDC, -8VDC, -12VDC & -15VDC. Similarly, the input should be in between +18VDC to +21VDC for positive output voltage power supplies +3VDC, +5VDC, +8VDC, +12VDC & +15VDC. ​ All the output Voltages are generated using fixed voltage regulator ICs, 7805, 7808, 7812, 7815 for positive voltages and 7905, 7908, 7912 & 7915 for negative voltages. For +3V, adjustable positive regulator IC LM317 and for -3V, adjustable negative voltage regulator IC LM337 are used with resistances 330 Ω and 220 Ω for fixed voltage outputs. ​ Refer full circuit diagram: Two berg strip sets are used on the PCB, for Positive and Negative Voltage outputs separately, for easy connection as per individual's requirements. GOOD LUCK. ENJOY.

microcontroller - COUNTERS & TIMERS Almost all micro controllers have one or more inbuilt counters. They are either 8 bit or 16 bit counters. The input for the counters may be from either external pins or internal system clock through pre-scalars. The current counter value is always saved to a register in the micro-controller and may directly access the value at any time. ​ Delay is one of the commonly used timer function, which is single use timer and not so accurate when compared to the internal programmed timers. Delay works on counting the ticks of micro-controller system clock frequency. If the counter is programmed for external input , then the counter register may either increase or decrease by 1, by changing the logic (voltage) at the programmed pin of micro controller. You can access the value in the register and may show on a displaying device. This type of programming is useful for event counter project etc. In case, the counter is read for every one second and reset to zero after reading the current value, then the programming may be used as frequency counter project. For programming as internal counter , the counter should receive signal from system clock frequency through pre-scalar circuit. The pre-scalar divides the system clock frequency by the value set in the pre-scalar register. In case, the counter register is full (i.e., exceeds its capacity), then it resets and starts counting again. An Interrupt may be activated when the particular counter register is full and resets, which calls COUNTER OVERFLOW SERVICE ROUTINE . Every time the counter is full or overflown, the Interrupt service routine is called, where you may program do specific tasks. This Interrupt is very useful to get exact and fixed time period, to do some specific operations in loop at a particular time period. These are called Timers in micro-controllers. ​ These timers are used for data aquisition system, frequency generation, wave form generation etc.

DIODES: A Diode allows flow of current in one direction and prevents (blocks) it in opposite direction. In other words, diode allows current flow from higher potential to lower potential only. Diode Identification: Diodes are available in different sizes and shapes. Normally a diode is identified with 1N as prefix and four digit number as suffix. The prefix 1N indicates one P-N junction. ​ ​ P-N junction means Positive(Anode) [marked as P in figures] and Negative(Cathode) [marked as N in figures] junction with two connections (conductors) connected to Anode[P] and Cathode [N] sides. The Negative (Cathode) is marked with a band, like white band on black surface or black band on glass surface. Diode Bias: If the positive terminal of DC power supply is connected to Anode of the diode and negative terminal of the DC power supply is connected to Cathode of the diode through some load (or resistance), the current flows through the diode. This is called Forwad bias connection of a diode. Only current (Amps) is the limiting factor, which flows through the diode, in case of forward bias. About 0.7V will be dropped across the Silicon diode and about 0.3V will dropped across the Germanium diode. ​ If the positive terminal of DC power supply is connected to Cathode of the diode and negative terminal of the DC power supply is connected to Anode of the diode through some load (or resistance), the flow of current is blocked through the diode. This is called Reverse bias connection of a diode. The Voltage applied across the diode should be less than breakdown voltage of the diode, in case of Reverse bias Diode Specifications: The main specifications of a diode are BREAKDOWN VOLTAGE, CURRENT CARRYING CAPACITY and RESPONSE TIME ON VOLTAGE REVERSAL. ​ Breakdown Voltage is the maximum voltage, that the diode withstands, before damage, applied across the diode in reverse biased. ​ The size (i.e, diameter or cross-sectional area) of a diode indicates current carrying capacity. Higher diameter or higher cross-sectional area of diode, means more current allowed to flow through the diode. ​ The minimum time taken by a Diode to allow flow and prevention of current is called Response time. The less response time means, works better with high frequencies in rectifier circuits. ​ The basic data of highly used Diodes are shown below for quick reference.(refer DATASHEET for exact full details) Diode as Rectifier: Diode is frequently used to convert AC power supply to DC power supply. When a diode is connected in series with AC power supply with some load, either positive half wave or negative half wave is appeared across the load due to forward bias. The other half wave will be blocked by the diode due to reverse bias. This is called Half-wave rectifier Let us understand all four possible cases as shown in the above figure. ​ Case 1A : when AC supply is +ve in upper conductor , -ve in lower conductor and the diode’s P is connected to upper conductor, then the diode is in forward bias and the half cycle of AC supply is appeared across the load. ​ Case 1B : when AC supply is -ve in upper conductor , +ve in lower conductor and the diode’s P is connected to upper conductor, then the diode is in reverse bias and the diode blocks the half cycle of AC supply. Which means, there is no supply across the load. ​ Case 2A : when AC supply is +ve in upper conductor , -ve in lower conductor and the diode’s N is connected to upper conductor, then the diode is again in reverse bias and the diode blocks the half cycle of AC supply. Which means, there is no supply across the load in this case also. ​ Case 2B : when AC supply is -ve in upper conductor , +ve in lower conductor and the diode’s N is connected to upper conductor, then the diode is in forward bias again and the half cycle of AC supply is appeared across the load Diodes in Bridge Rectifier: If single diode is used as rectifier in AC circuit, half of the AC cycle is lost in the output (load). So, to overcome this problem, four diodes are used for full wave rectification, which is called as Bridge rectifier. In a Bridge Rectifier, four diodes are arranged in a particular format. Anodes of two diodes are connected together and Cathodes of other two diodes are connected together. The left out connectors of two sets of diodes connected in a Diamond form with free Anode of one diode connected to Cathode of another free diode. AC signal is applied at anode-cathode junctions and the rectified output of Positive and Negative voltages are obtained at Anodes junction and Cathodes junction respectively When an AC signal is applied at Anode-Cathode junctions of bridge rectifier, the output is always positive at Anode junctions and the output is always negative at Cathode junctions, which is shown here as graphical representation. Considering first case, as the connections of AC supply may be positive and negative on the two conductors, the working of the diodes in bridge rectifier may be understand from the above figure WORKING CONDITION-1. In case, the AC supply is negative and positive (reverses) on the same two conductors, the working of the diodes in the same bridge rectifier may be understand from the figure WORKING CONDITION-2. A practical circuit for AC to DC conversion circuit using bridge rectifier is shown here. The obtained output is full wave DC. Full Wave Rectifier using TWO Diodes: Some transformers have center tapping in secondary winding. In that case, the middle tapping may be used as ground and the extreme tappings may be connected to two diodes for full wave rectification as shown here. ZENER DIODES: Zener Diodes are used to have fixed voltage reference. When a zener diode is used in reverse bias, the PN junction maintains certain voltage across the PN junction and it will have fixed value. So, zener diode is used in reverse bias only. Cathode is identified by a black band on zener diode In practice a resistance is used in series with a zener diode in reverse bias mode and the voltage across the zener diode is used as reference voltage. ​ Zener diodes are available in various voltages(2.7V, 3V, 3.3V, 4.7V 12V, 15V etc.) and various wattages (025W, 0.5W, 1W etc.). ​ The wattage may be identified by the diameter (or size), where as it is some what difficult to read the voltage marked on the zener diode. Some times it is difficult differentiate zener diode with signal diode (1N4148).