Electronic Circuits and Diagram-Electronics Projects and Design

This article is about interfacing a hex key pad to 8051 microcontroller. A clear knowledge on interfacing hex key pad to 8051 is  very essential  while designing embedded system projects which requires character or numeric input or both. For example projects like digital code lock, numeric calculator etc. Before going to the interfacing in detail, let’s have a look at the hex keypad. Hex keypad. Hex key pad is essentially a collection of 16 keys arranged in the form of a 4×4 matrix. Hex key pad usually have keys representing numerics 0 to 9 and characters A to F. The…

Delay using 8051 timer.  The 8051 microcontroller has two independent 16 bit up counting timers named Timer 0 and Timer 1 and this article is about generating time delays using the 8051 timers. Generating delay using pure software loops have been already discussed here but such delays are poor in accuracy and cannot be used in sensitive applications. Delay using timer is the most accurate and surely the best method. A timer can be generalized as a multi-bit counter which increments/decrements itself on receiving a clock signal and produces an interrupt signal up on roll over. When the counter is…

Software delay routine in 8051 In an 8051 microcontroller, it requires 12  cycles of the processor clock for executing a single instruction cycle.  For an 8051 microcontroller clocked by a 12MHz crystal, the time taken for executing one instruction cycle is 1µS and it is according to the equation,  Time for 1 instruction cycle= 12 /12MHz = 1µS.  The shortest instructions will execute in 1µS and other instructions will take 2 or more micro seconds depending up on the size of the instruction. Thus a time delay of any magnitude can be generated by looping suitable instructions a required number…

Random number generator using 8051. A  random number generator using 8051 that  displays a random number between 0 & 99 is shown in this article. The circuit it self is very simple and may not find any applications in serious embedded projects and this article is just an illustration. The circuit is based on AT89S51 microcontroller, two seven segment LED displays, two transistors and few passive components. Circuit diagram. The two seven segment LED displays are multiplexed together and their data lines are connected to Port0  of the microcontroller. Transistors Q1 and Q2 drives the corresponding displays D1 and D2….

Voltmeter using 8051. A simple 0-5V voltmeter using 8051 is shown in this article. This digital voltmeter has a sensitivity of  200mV which is a bit low but this project is meant for demonstrating how an ADC and seven segment display can be interfaced to 8051 to obtain a digital readout of the input voltage. A 31/2 digit high end voltmeter will be added soon. ADC0804 is the ADC and AT89S51 is the controller used in this project. Before attempting this project, go through these projects Interfacing ADC to 8051 and Interfacing seven segment display to 8051 which will give you a…

This article shows how to interface a DC motor to an 8051 microcontroller. Interfacing DC motor to 8051 forms an essential part in designing embedded robotic projects. A well designed 8051-DC motor  system  has essentially two parts. Firstly an 8051 with the required software to control the motor and secondly a suitable driver circuit. Most of the DC motors have  power requirements well out of the reach of a microcontroller and more over the voltage spikes produced while reversing the direction of rotation could easily damage the microcontroller. So it is not wise to connect a DC motor directly to the…

A Note about 7 segment LED display. This article is about how to interface a seven segment LED display to an 8051 microcontroller. 7 segment LED display is  very popular and it can display digits from 0 to 9 and quite a few characters like A, b, C, ., H, E, e, F, n, o,t,u,y, etc. Knowledge about how to interface a seven segment display to a micro controller is very essential in designing embedded systems. A seven segment display consists of seven LEDs arranged in the form of a squarish ’8′ slightly inclined to the right and a single…

In this article, I would like to introduce you to the concept of interrupts, how interrupts work, vector address, interrupt priority and how to write an ISR (interrupt service routine). “Interruption” in English language means a deviation from the normal routine. We know the processor is always busy executing some kind of instructions. What if there  occurs an urgent condition that we need to pause the processor from its current activities for some time and make it execute/do something else? Also we need to resume the processor back to its operations after executing our “urgent condition”. To meet such a…

This article is all about how to interface push button switches to an 8051 microcontroller. Push button switches are widely used in embedded system projects and the knowledge about  interfacing them to  8051 is very essential in designing such projects. A typical push button switch has two active terminals that are normally open and these two terminals get internally shorted when the push button is depressed. Images of a typical pushbutton switch is shown below. Circuit diagram. The circuit diagram for interfacing  push button switch to 8051 is shown above. AT89S51 is the microcontroller used here. The circuit is so designed that…

This article series is developed to teach you 8051 micro controller programming. I have divided this programming tutorial into a series of chapters as shown below. So you can start with Chapter 1 and then move to chapter 2 and chapter 3 and so on. So let’s begin the journey right now!  Note: Next chapters 1,2,3.. are under development phase. Please visit this page again for updates. Note: To test any of these program or to write one your own and test, you dont need to buy a microcontroller board now. You can test your program using an 8051 simulator….