Free Elektor Circuit: Magic Key
An infra-red remote control for an (electromagnetically operated) lock? Nothing special, you will think. But some umpteen years ago this looked like magic, and it was very satisfying to build something like that yourself. Even if it was only to amaze the neighbors. Here you can see how it was achieved, using only a small number of components.
First we need a transmitter, which produces some kind of IR signal. To keep things uncluttered, a simple 555 oscillator is used which produces a rectangular wave at a frequency of 3.5 kHz having a duty cycle of 75% (the output is high 75% of the time and low 25% of the time) – see Figure 1.
Free Elektor Circuit: Magic Key – [Link]