Use your Symbian OS mobiles to control devices through Bluetooth.
The serial to Bluetooth converter is used in this project. The Microcontroller At89C2051 is used to receive the data from the mobile through bluetooth.
Before using the bluesmirf, change the baud rate to 19200, because the default baud rate is 115200.
Most of the Nokia Smart phones can be used in this project.
Here’s the another design which uses AUBTM-22 serial to Bluetooth module.
The only difference from the sparkfun module circuit is, this module works on 3.3v so the microcontroller is also operated by the 3.3v power supply.
The module have a default baud rate of 9600, so you have to change the program, since the Sparkfun module works on 19200 baud rate.
The pairing code for this module is 8888
Look around. Notice the smart “intelligent” systems? Be it the T.V, washing machines, video games, telephones, automobiles, aero planes, power systems, or any application having a LED or a LCD as a user interface, the control is likely to be in the hands of a micro controller!
Measure and control, that’s where the micro controller is at its best.
Micro controllers are here to stay. Going by the current trend, it is obvious that micro controllers will be playing bigger and bigger roles in the different activities of our lives.
So where does this scenario leave us? Think about it……
The world of Micro controllers
What is the primary difference between a microprocessor and a micro controller? Unlike the microprocessor, the micro controller can be considered to be a true “Computer on a chip”.
In addition to the various features like the ALU, PC, SP and registers found on a microprocessor, the micro controller also incorporates features like the ROM, RAM, Ports, timers, clock circuits, counters, reset functions etc.
While the microprocessor is more a general-purpose device, used for read, write and calculations on data, the micro controller, in addition to the above functions also controls the environment.
We have used a whole lot of technical terms already! Don’t get worried about the meanings at this point. We shall understand these terms as we proceed further
For now just be aware of the fact, that all these terms literally mean what they say.
Bits and Bytes
Before starting on the 8051, here is a quick run through on the bits and bytes. The basic unit of data for a computer is a bit. Four bits make a nibble. Eight bits or two nibbles make a byte. Sixteen bits or four nibbles or two bytes make a word.
1024 bytes make a kilobyte or 1KB, and 1024 KB make a Mega Byte or 1MB.
Thus when we talk of an 8-bit register, we mean the register is capable of holding data of 8 bits only.
The 8051
The 8051 developed and launched in the early 80`s, is one of the most popular micro controller in use today. It has a reasonably large amount of built in ROM and RAM. In addition it has the ability to access external memory.
The generic term `8×51` is used to define the device. The value of x defining the kind of ROM, i.e. x=0, indicates none, x=3, indicates mask ROM, x=7, indicates EPROM and x=9 indicates EEPROM or Flash.
A note on ROM
The early 8051, namely the 8031 was designed without any ROM. This device could run only with external memory connected to it. Subsequent developments lead to the development of the PROM or the programmable ROM. This type had the disadvantage of being highly unreliable.
The next in line, was the EPROM or Erasable Programmable ROM. These devices used ultraviolet light erasable memory cells. Thus a program could be loaded, tested and erased using ultra violet rays. A new program could then be loaded again.
An improved EPROM was the EEPROM or the electrically erasable PROM. This does not require ultra violet rays, and memory can be cleared using circuits within the chip itself.
Finally there is the FLASH, which is an improvement over the EEPROM. While the terms EEPROM and flash are sometimes used interchangeably, the difference lies in the fact that flash erases the complete memory at one stroke, and not act on the individual cells. This results in reducing the time for erasure.
Understanding the basic features of the 8051 core
Let’s now move on to a practical example. We shall work on a simple practical application and using the example as a base, shall explore the various features of the 8051 microcontroller.
Consider an electric circuit as follows,
The positive side (+ve) of the battery is connected to one side of a switch. The other side of the switch is connected to a bulb or LED (Light Emitting Diode). The bulb is then connected to a resistor, and the other end of the resistor is connected to the negative (-ve) side of the battery.
When the switch is closed or ‘switched on’ the bulb glows. When the switch is open or ‘switched off’ the bulb goes off
If you are instructed to put the switch on and off every 30 seconds, how would you do it? Obviously you would keep looking at your watch and every time the second hand crosses 30 seconds you would keep turning the switch on and off.
Imagine if you had to do this action consistently for a full day. Do you think you would be able to do it? Now if you had to do this for a month, a year??
No way, you would say!
The next step would be, then to make it automatic. This is where we use the Microcontroller.
But if the action has to take place every 30 seconds, how will the microcontroller keep track of time?
Execution time
Look at the following instruction,
clr p1.0
This is an assembly language instruction. It means we are instructing the microcontroller to put a value of ‘zero’ in bit zero of port one. This instruction is equivalent to telling the microcontroller to switch on the bulb. The instruction then to instruct the microcontroller to switch off the bulb is,
Setb p1.0
This instructs the microcontroller to put a value of ‘one’ in bit zero of port one.
Don’t worry about what bit zero and port one means. We shall learn it in more detail as we proceed.
There are a set of well defined instructions, which are used while communicating with the microcontroller. Each of these instructions requires a standard number of cycles to execute. The cycle could be one or more in number.
How is this time then calculated?
The speed with which a microcontroller executes instructions is determined by what is known as the crystal speed. A crystal is a component connected externally to the microcontroller. The crystal has different values, and some of the used values are 6MHZ, 10MHZ, and 11.059 MHz etc.
Thus a 10MHZ crystal would pulse at the rate of 10,000,000 times per second.
The time is calculated using the formula
No of cycles per second = Crystal frequency in HZ / 12.
For a 10MHZ crystal the number of cycles would be,
10,000,000/12=833333.33333 cycles.
This means that in one second, the microcontroller would execute 833333.33333 cycles.
Therefore for one cycle, what would be the time? Try it out.
The instruction clr p1.0 would use one cycle to execute. Similarly, the instruction setb p1.0 also uses one cycle.
So go ahead and calculate what would be the number of cycles required to be executed to get a time of 30 seconds!
Getting back to our bulb example, all we would need to do is to instruct the microcontroller to carry out some instructions equivalent to a period of 30 seconds, like counting from zero upwards, then switch on the bulb, carry out instructions equivalent to 30 seconds and switch off the bulb.
Just put the whole thing in a loop, and you have a never ending on-off sequence.
Simple isn’t it?
Let us now have a look at the features of the 8051 core, keeping the above example as a reference,
1. 8-bit CPU.( Consisting of the ‘A’ and ‘B’ registers)
Most of the transactions within the microcontroller are carried out through the ‘A’ register, also known as the Accumulator. In addition all arithmetic functions are carried out generally in the ‘A’ register. There is another register known as the ‘B’ register, which is used exclusively for multiplication and division.
Thus an 8-bit notation would indicate that the maximum value that can be input into these registers is ‘11111111’. Puzzled?
The value is not decimal 111, 11,111! It represents a binary number, having an equivalent value of ‘FF’ in Hexadecimal and a value of 255 in decimal.
We shall read in more detail on the different numbering systems namely the Binary and Hexadecimal system in our next module.
