Ppt on interfacing led and 7 segmentwith 8951
- 2. 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.
- 3. Light Emitting Diodes are the semi conductor light sources. Commonly used LEDs will have a cut-off voltage of 1.7V and current of 10mA. When an LED is applied with its required voltage and current it glows with full intensity. The Light Emitting Diode is similar to the normal PN diode but it emits energy in the form of light.
- 4. 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.
- 5. 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.
- 6. Light Emitting Diodes are the semi conductor light sources. Commonly used LEDs will have a cut-off voltage of 1.7V and current of 10mA. When an LED is applied with its required voltage and current it glows with full intensity. The Light Emitting Diode is similar to the normal PN diode but it emits energy in the form of light. The colour of light depends on the band gap of the semiconductor. The following figure shows “how an LED glows?”
- 7. 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.
- 8. 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.
- 12. Seven segment displays are used to indicate numerical information. Seven segments display can display digits from 0 to 9 and even we can display few characters like A, b, C, H, E, e, F, etc. These are very popular and have many more applications. Before going to start this concept, get an idea about how to interface LEDs with 8051 Microcontroller.
- 13. 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.
- 15. Interfacing 7 Segment Display to 8051 Circuit Diagram:
- 16. 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.
- 18. Digit Drive Pattern: To display the digits on 7 segment, we need to glow different logic combinations of segments. For example if you want to display the digit 3 on seven segment then you need to glow the segments a, b, c, d and g. The below table show you the Hex decimal values what we need to send from PORT2 to Display the digits from 0 to 9. Digit Dp g f e d c b a Hex value 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
- 19. 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.