This circuit remote control Kit Universal ,every one could make and have fun, This one day that i was trying to control the TV from the serial port of the computer. 
It took me no more than a few minutes to understand the simple method that the remote controls work.
Because this circuit is easy enough for everyone to make, i decided, instead of writing how this circuit remote control.
Although there are tutorial make schema a remote control Kit Universal, spec papers and tutorials on how those remotes work, i wanted to do it my way. I connected the oscilloscope on the IR LED of my remote control and after some key presses and range selects, the signal revealed.
According to what key we press, the transmitter will send this pattern, and the code bits shall change. The buttons that i chose to send are not random. I run some tests and saw that when the numeric keys are pressed, the code bits will have the binary number of each button.
The first code was sent when we pressed the button 1, and the second code was sent when we pressed key 2.
It should be taken into account that the delay from pulse to pulse, AKA period of the signal is approximately 1mSec. This is good to know for other projects, but for this project is irrelevant.
Now you should be able to predict the whole series of code that will be sent when we press number 4 of the transmitter.
The range is approximately from 11.5KHz to 56KHz, enough for almost every remote control on the market.
You could add optionally a switch in series with the power source. The voltage can climb up to +5 volts, but resistors that polarizes the transistors needs to be re-calculated. It would not increase the range though, unless you add more IR LEDs.
How to make a remote control Kit Universal
