Interfacing of electronic switch with 8051

• What is electronics switch? – A switch is an electrical component that can break an electrical circuit, interrupting the current or diverting it from one conductor to another. There are two main state of switch “open” and “close”. And each switch has a mechanism that is “toggle” or “momentary”. Toggle mean flip switch for continuous  “on”  or  “off”. Momentary mean push-for “on” or push-for “off”.

• Types of electronic switch –

Type	Type expansion	Description	Symbol
SPST	Single pole single throw	A simple on-off switch: The two terminals are either connected together or disconnected from each other. An example is a light switch
SPDT	Single pole double throw	A simple changeover switch: C (COM, Common) is connected to L1 or to L2.
SPTT or SPCO	Single pole triple throw or single pole change over	Similar to SPDT. Some suppliers use SPCO/SPTT for switches with a stable off position in the centre and SPDT for those without
DPST	Double pole single throw	Equivalent to two SPST switches controlled by a single mechanism
DPDT	double pole double throw	Equivalent to two SPDT switches controlled by a single mechanism.
DPCO	Double pole changeover	Schematically equivalent to DPDT. Some suppliers use DPCO for switches with a stable center position and DPDT for those without. A DPDT/DPCO switch with a center position can be “off” in the center, not connected to either L1 or L2, or “on”, connected to both L1 and L2 at the same time. The positions of such switches are commonly referenced as “on-off-on” and “on-on-on” respectively.
2P6T	two pole six throw	Changeover switch with a (COM, Common) which can connect to L1, L2, L3, L4, L5, or L6; with a second switch (2P, two pole) controlled by a single mechanism
INTERMEDIATE SWITCH	Intermediate switch	DPDT switch internally wired for polarity-reversal applications: only four rather than six wires are brought outside the switch housing.

• Operation – We can interface a switch to microcontroller by two way as shown in above image.

1. 1.   Connecting switch by Vcc and MCU (SW1) – detecting switch by logic ‘1’ at port pin when switch is pressed (here pin 0 of port 0).
2. 2.   Connecting switch by GND and MCU (SW2) – detecting switch by logic ‘0’ at port pin when switch is pressed (here pin 1 of port 0).

• Applications- Different types of switches are used according to different parameters. Like computer keyboard and mobile keypad are use momentary SPST switches. Home Appliances use SPDT switches.

1. Circuit diagram of two electronic switch ,8 led and seven segment connected with 8051

1. Program of  Control Led Blinking Using  electronic  Switch  With 8051 

/******************************************************
IDE :- Keil
DEVELOPED BY:- FIRMWARE DEVELOPER (www.firmcodes.com)
WHAT PROGRAM DO:- BLINKING OF LED CONTROLLED BY ELECTRONIC SWITCH
******************************************************/

#include<reg51.h>

sbit switch1=P1^0;  // pin P1.0 IS accessed as  a variable name switch1 

sfr led=0xa0;       // port P2 IS accessed as a variable name led

void main()
   {
	switch1=0;  // make pin P1.0 as INPUT MODE
	while(1)
	   {
		if(switch1==1)        //check switch is pressed or not
			led=0xff;     // led on
		else
			led=0x00;    // led off
         }
   }

PROTEUS File for SIMULATION(Password Of RAR file is :-firmcodes.com)

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2. Program of  Two ELECTRONIC SWITCH  one for LED other for 7 SEGMENT  With 8051

******************************************************
www.firmcodes.com
DEVELOPED BY:- FIRMWARE DEVELOPER
WHAT PROGRAM DO:- TWO ELECTRONIC SWITCH ,ONE CONTROL LED BLINKING AND OTHER CONTROL COUNTING OF 7 SEGMENT
******************************************************
#include<reg51.h>
sfr led=0xa0;         // led at port 2
sfr seven_seg=0xb0;   // seven segment at port 3
sbit switch1=P1^0;    // switch1 at pin P1.0
sbit switch2=P1^1;     // switch2 at pin P1.1
void delay()
int data1[]={0xc0,0xf9,0xa4,0xb0,0x99,0x92,0x82,0xf8,0x80,0x90}; // data of common anode
void main()
   {
	int i=0,j;
	switch1=switch2=0;
	while(1)
	   {
		if(switch1==1)  // switch 1
		   {
			led=0xff;     // led on
			delay();
			led=0x00;     // led off
			delay();
                    }
		else if(switch2==1)  // switch 2
		   {
			 if(i==10)
				 i=0;
			 seven_seg=data1[i];
			 for(j=0;j<50;j++)
			 delay();
			 i++;
                    }
              }
    }

void delay()
  {
	int i;
	for(i=0;i<3000;i++);
  }
***************************************************************************
End program
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***************************************************************************

PROTEUS File for SIMULATION(Password Of RAR file is :-firmcodes.com)

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