8051 interfacing switches & leds

8/17/2019 8051 Interfacing Switches & LEDs

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8.8051 INTERFACING:SWITCHES & LEDS

ObjectiveIn this tutorial, we will see how we could interface a simple switch to micrcontroller. Yes, it is indeed very

simple, later in this tutorial we will do some logical operations with LEDs and Switches.

Switc !"#ic#

If we directly connect a switch to one of the microcontroller port pins, the pin floats when the switch is open.

Meaning, it is not at a fixed logic level v or !v. "ence we pull the pin up through a resistor to !v(LOGIC 1),

as shown in the figure #. $ow, whenever the switch is pressed, it grounds(LOGIC 0) the port pin.

$ow we could go ahead and interface it to the microcontroller, %ut we would rather interface & switches and &

LED's to two ports as shown in the schematic %elow.

Sce$"tic


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(igure )* Schematic Diagram

+s we can see the schematic has %asic circuits for oscillator, reset and power connections for the

micrcontroller.

• + DI -dual in line pacage/ Switch, array of & switches is connected to PORT3 +$D & LEDs

to PORT2.

• 0%serve the RR1 component, it is array of & resistors in a single pac-SI/. It is as good as connecting

& pullup resistors as shown in figure #. You could also use & discrete resistors as well.

Experiments

1. Re" Switce# "' Di#()"* St"t+# ,' LED#

1his a very simple one, configure 0213 -switches/ as inputs and 021) -LEDs/ as outputs4 read the switch

status and display on LEDs.

1he code for the pro5ect is listed %elow*


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• 1he LEDS and S6I17"ES as defined and assigned to ) and 3 respectively.

• S6I17"ES-3 is made input/

• 1he switches are read and status is displayed on LEDS continously.

1. Read Switches and Display Status on LEDs

#include

#define SW!"ES $%

#define LEDS $&

'oid (ain)*

+

unsigned char switchnput,

SW!"ES - /ff, /*Configure SWITCHES as Input */

while)1*

+

switchnput - SW!"ES, /* Get the SWITCH combination */

LEDS- switchnput, /* Dispaly the SWITCH I/P on EDS */

0

0

). Logical 0perations with LEDs and Switches

(or this experiment, we will divide switches into three groups as shown in ta%le #. Switches connected to P3.7

and P3.6 are 0perators,they are selected as shown in ta%le ) to perform bit-wise logical operations on Grou

! and Grou ".

Tab#e$1

Oeration Grou ! Grou "

3.8 3.9 3.! 3.: 3.3 3.) 3.# 3.

Tab#e 2$

P3.7 P3.6 Oeration


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+$D

# 02

# ;02

# # I$


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break,

case /&7 result - group2 9 group3, /* Perform 10 operation*/

break,

case /%7 result - ):group2* /6, /*In2ert 2alue ofgroup'*/

break,

default7 result - /,

break,

0

LEDS- result, /* 3inally 4ispaly the result on the

EDS */

0

0

Switce#/"'&/LED#.0i(

8051 interfacing switches & leds

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