Ppt on interfacing led and 7 segmentwith 8951
- 2. LED:- An LED or Light Emitting Diode, is a solid state optical PN-junction diode which emits light energy in the form of “photons” when it is forward biased by a voltage allowing current to flow across its junction, and in Electronics we call this process electroluminescence.
- 3. A light emitting diode (LED) is essentially a PN junction opto-semiconductor that emits a monochromatic (single color) light when operated in a forward biased direction. LEDs convert electrical energy into light energy. They are frequently used as "pilot" lights in electronic appliances to indicate whether the circuit is closed or not The most important part of a light emitting diode (LED) is the semi-conductor chip located in the center of the bulb as shown at the right. The chip has two regions separated by a junction. The p region is dominated by positive electric charges, and the n region is dominated by negative electric charges. The junction acts as a barrier to the flow of electrons between the p and the n regions. Only when sufficient voltage is applied to the semi-conductor chip, can the current flow, and the electrons cross the junction into the p region.
- 4. When sufficient voltage is applied to the chip across the leads of the LED, electrons can move easily in only one direction across the junction between the p and n regions. In the p region there are many more positive than negative charges. When a voltage is applied and the current starts to flow, electrons in the n region have sufficient energy to move across the junction into the p region. Each time an electron recombines with a positive charge, electric potential energy is converted into electromagnetic energy. For each recombination of a negative and a positive charge, a quantum of electromagnetic energy is emitted in the form of a photon of light with a frequency characteristic of the semi-conductor material (usually a combination of the chemical elements gallium, arsenic and phosphorus)..
- 5. Testing LEDs:- Never connect an LED directly to a battery or power supply! It will be destroyed almost instantly because too much current will pass through and burn it out. LEDs must have a resistor in series to limit the current to a safe value, for quick testing purposes a 1k resistor is suitable for most LEDs if your supply voltage is 12V or less.
- 6. Applications:- • Sensor Applications • Mobile Applications • Sign Applications • Automative Uses • LED Signals • Illuminations • Indicators
- 8. The circuit mainly consists of AT89C51 microcontroller. AT89C51 belongs to the family of 8051 microcontroller. It is an 8-bit microcontroller. This microcontroller has 4KB of Flash Programmable and Erasable Read Only Memory and 128 bytes of RAM. This can be programmed and erased maximum 1000times. It has two 16 bit timers/counters. It supports USART communication protocol. It has 40 pins. There are four ports are designated as P0, P1, P2, P3, P4.
- 9. The Anode is connected through a resistor to GND & the Cathode is connected to the Microcontroller pin. So when the Port Pin is HIGH the LED is OFF & when the Port Pin is LOW the LED is turned ON.
- 10. In this circuit, LEDs are connected to the port P0. Port P0 will not have internal pull- ups, while the other ports have internal pull-ups. The controller is connected with external crystal oscillator to pin 18 and 19 pins. Crystal pins are connected to the ground through capacitors of 33pf.using an LED you must use a resistor to limit the current flow. If you just connect an LED directly to a pin of the micro controller you run the risk of damaging the micro controller by allowing too much current flow into or out of the pin.
- 11. Thus, LED is directly connected to the AT89C51 microcontroller. The negative terminal of the LED is connected to the ground through a resistor. Value of this resistor is calculated using the following formula. , where V is the input voltage. R= (V-1.7)/10mA Generally, microcontrollers output a maximum voltage of 5V. Thus the value of resistor calculated for this is 330 Ohms. Thus this can be connected either to the cathode or anode of the LED.
- 14. Program for 7 Led glow org 00h clr a mov p2,a start: mov a,#0ffh mov p2,a mov p2,#01h call delay mov p2,02h call delay mov p2,#04h call delay mov p2,08h call delay mov p2,#10h call delay mov p2,#20h call delay mov p2,#40h call delay mov p2,#80h call delay jmp start delay: mov r0,#255 h1: mov r1,#255 h2: djnz r1,h2 djnz r0,h1 ret end
- 15. LED Interfacing with 8051 Circuit Applications: LEDs are widely used in many applications like in seven segments. They are used in dot matrix displays. They can be used for street lights. They are used as indicators. They can be used in traffic lights. They are used in emergency lights They can used to make electronic designs.
- 17. 7 segment display :- 7 segment display is a 10 pin electronic component with eight led’s embedded inside it to displays number from 0 to 9 even we can display few characters like A, b, C, H, E, e, F, etc. . It is available in two configurations: common cathode and common anode. A seven segment display consists of seven LEDs arranged in the form of a “squarish eight” slightly inclined to the right and a single LED as the dot character. Different characters can be displayed by selectively glowing the required LED segments.
- 18. Seven segment displays are of two types:- 1. Common anode 2. Common Cathode In Common Anode configuration the pin 3 and 8 are shorted together with Anode of all 8 LED segments and this common pin is connected to positive voltage (VCC).Hence to light up any given segment the corresponding Cathode pin should be connected to ground or reference ,which completes the circuit and LED will be in forward bias.
- 19. In Common Cathode configuration the pin 3 and 8 are shorted together with Cathode of all 8 LED segments and this common pin is connected to Ground or reference point. Here if you give positive voltage to corresponding LED Anode pin the circuit will be completed and the particular LED will be light up since it will be in forward bias. Digit Dp g f e d c b a Hex valu e 0 0 0 1 1 1 1 1 1 0x3f 1 0 0 0 0 0 1 1 0 0x06 2 0 1 0 1 1 0 1 1 0x5b 3 0 1 0 0 1 1 1 1 0x4f 4 0 1 1 0 0 1 1 0 0x66 5 0 1 1 0 1 1 0 1 0x6d 6 0 1 1 1 1 1 0 1 0x7d 7 0 0 0 0 0 1 1 1 0x07 8 0 1 1 1 1 1 1 1 0x7f 9 0 1 1 0 0 1 1 1 0x67
- 20. Interfacing 7 Segment Display to 8051 Circuit Principle: Seven segment displays internally consist of 8 LEDs. In these LEDs, 7 LEDs are used to indicate the digits 0 to 9 and single LED is used for indicating decimal point. Generally seven segments are two types, one is common cathode and the other is common anode. In common cathode, all the cathodes of LEDs are tied together and labeled as com. and the anode are left alone. In common anode, seven segment display all the anodes are tied together and cathodes are left freely. Below figure shows the internal connections of seven segment Display.
- 21. Interfacing 7 Segment Display to 8051 Circuit Diagram:
- 22. Program for 7 Segment for displaying Number (0 to 9):- org 00h clr a mov p2,a start: mov p2,#0c0h call delay mov p2,#0f9h call delay mov p2,#0a4h call delay mov p2,0b0h call delay mov p2,#99h call delay mov p2,#92h call delay mov p2,#82h call delay mov p2,#0f8h call delay movp2,#80h call delay movp2,#98h call delay jmp start delay: mov r0,#255 h1: mov r1,#255 h2:mov r3,#255 h3:djnz r3,h3 djnz r2,h2 djnz r1,h1 ret end
- 23. Interfacing 7 Segment Display to 8051 Circuit Design: Here, common cathode seven segment is used to display the digits. In this circuit, pins a to h of the 7 segment are connected to the PORT 2 of the microcontroller and com pin is connected to the ground through the 330 ohm resistor. This resistor is used to drop the voltage. Since we are using common cathode seven segment we need to send LOGIC 1 to the segments to glow. Figure shows structure of common cathode seven segments. Here dot is used for indicating the decimal point. Here all the cathodes of LED’s are connected to the Gnd pin. The operating voltage of this LED’s is 2 to 3V but from controller we will get 5V so to drop the remaining voltage we have to connect a to g pins to the controller through the resistor.
- 24. Interfacing 7 Segment Display to 8051 Circuit Applications: Seven segments are widely used in digital clocks to display the time. These are used in electronic meters for displaying the numerical information. Used in Instrument panels Used in digital readout displays.