8051 SWITCH INTERFACE

It is necessary for every system to have proper user interface - which makes it user friendly and easy to operate. For instance, imagine using your computer without the monitor (display), keyboard or mouse? It's not even possible to operate it without these essential components as they help you either in entering data (input) to the PC or seeing the results on screen (output). Similarly, an embedded system (the one involving microcontrollers such as 8051 in our case) also require input/ouput devices to be user friendly. A switch can act as an input device to the microcontroller unit (MCU) and this post is all about interfacing/connecting it to the 8051 MCU.

SWITCHES

Switches come in many different shapes and sizes. The main idea or function is to either enable or disable something by simply turning it on/off. Thus it acts as an input device that users can use to control certain parts of the system. Below are the most common switches that you will come across

Push Button

DIP (Dual in-line Package) Switch

ON-OFF Switch

In circuit diagrams, a switch is generally represented by 

Switch Symbol

After examining the Switch Symbol, I think it is quite clear how a switch actually works. It closes (connects) or opens (disconnects) a circuit. The Push Button behaves in the same fashion as it closes the circuit as long as you keep holding it in pressed state.  

8051 SWITCH INTERFACE

You can connect a switch to 8051 MCU using different configurations but the basic functionality remains the same. Always remember this cool fact that the user is never concerned about the actual implementation. He/she just wants something to turn ON when the switch is ON and vice versa OFF. As for you, you can handle it in many different ways. For example, you can connect a switch with 8051 MCU in the following ways (check the captions for comments)

GOOD - Safe to use

FAIR - Can be used without much consideration

POOR - too much current to the MCU

These are the conventional methods of switch interface that you will find around in the internet. The good news is that at least they work. There are certain configurations that you need to avoid and must never use. For instance, have a look at these

VERY POOR - circuit is SHORTED when Switch is ON

SERIOUSLY? Circuit SHORTED again

Now how about this one that I am thinking of? 

AWESOME - Safe to use

It looks quite simple and still works effectively. The tricky part is that turning ON the switch will actually generate a LOW signal (connected to ground) but you can use that to your advantage as discussed in the program code below.

SWITCH INTERFACE CODE

Here is the C language code for the Switch Interface with the 8051 microcontroller. I have also used an LED in this example. If you don't know how to interface LED to 8051, you must check this article here. You can download the source code as well as the compiled HEX file from the link given below.

SWITCH Interface C Language Code

Let me explain the code in a step wise fashion

• PIN1.0 is renamed as sw using #define directive (for convenience)
• Similarly PIN1.1 is renamed as led (LED is connected to this pin)
• sw is declared as input pin (for reading switch status)
• led is declared as output (for driving LED on/off)
• while( 1 ) is used to force MCU indefinitely work on this single task
• if ( !sw ) statement is true only if switch is ON (sw = 0 and !sw = 1) and thus led will glow
• Otherwise led will stay OFF

The same code simulated in Proteus looks like this (Proteus design file is also included in the package for your convenience)

Proteus Simulation

This concludes the topic for today. I hope that after reading this post, you have at least some basic idea of using a switch with the 8051 microcontroller. If you have ANY question, suggestion, or feedback please feel free to share in the comments section. Furthermore, do check my previous posts for more help.

DOWNLOAD ZIP

This ZIP package contains the following files

• C Language Code
• Compiled HEX file
• Proteus Design File

You can use all these files at your will but remember that they are for the sake of understanding the concept. You have to know what's going on and then it won't hurt if you just copy/paste but if you do it without caring about understanding, well all I can say is that it's not good for development.