Basic interface with hardware

I want Arduino to control other devices, for example: my HiFi amplifier, my TV, …

This may be in a clean and simple way, the more inocuos way.

1- Add something than can make a button press in the device connecting in parallel, so I can press the button manually and make Arduino “press” the button (but not a noisy relay)

2- Detect lighting leds. In parallel, detect the light, or the current in one led of de device without interfering in its usual function

3- More complex: Interface with some displays to know state of the device, and keeping display running

Please, can anybody give a simple approach? (1 y 2, i know 3 is too complex)

Other thing is how to make Arduino act as a potentiometer to substitute one on the device.

You can get digital potentiometers that can be contolled from Arduino.

Most audio and video gear these days comes with infrared remote controls. The "quiet, non-intrusive" way to control it is probably to make the Arduino pretend to be a handheld remote. I haven't looked too closely at them, because my interests lie elsewhere, but I've noticed several people's projects in this area when I was searching for other things.

There's a Linux project called "lirc" that has done a lot of research on interfacing PCs to IR remotes and devices controlled by them. They should have some info (like what devices use what IR codes) that you can use on your Arduno projects.

Ran

OK Ran, this is a very good solution for IR devices. I'll look for some project with IR remotes. But I don't want forget devices without IR (I'm thinking in someones I want to control), or with very particular IR codes (I have one universal remote that I can't use with a satellite decoder)