Question about tablet

WiFi? Bluetooth? USB? Light off the screen? Sound from the speaker? Mag field off the speaker?

You can get USB to digital output modules, someplace. Google around.

Check FTDI Semiconductor's website -- they put the FT230X onto a DIP module; they may do the same thing for at least one of their bit-bangable chips.

this one in clever:

uses one channel of the headphone/microphone jack for communication and harvest power from a tone output one the other audio channel

for Android there is a standard for USB called IOIO,

-Lasse

I assume you want it wireless. The easiest way is to build your controller module as WiFi AP and running a socket server. On the Android side, just a simple socket client.

Of course, I should have thought of the headphone output.

I just got few wifi modules with the ESP8266, out of the box it has a UART interface but you can donwload an SDK and write you own code for it, make a webserver, wiggle IO etc.

Work as both AP and STA

-Lasse

FT311 is specifically the right chip for Android devices that have USB-OTG. Android 4+ has a built-in driver and Java API that can drive the chip through any of its six modes (GPIO, UART, PWM, I2C, SPI master, SPI slave. Minimal external components.

---------------- Thank you guys for suggestion. In this project all comes down to costs. In the first place i was thinking on using some 5" or 7" lcd that can be hooked up to RPI. Now, i dont know if i can hook up this LCD to rpi but i guess i can. This would be the best solution because of GPIO but if i calculate the costs then i come to this calculation:

On the other side, tablet wouldd be cca $20 cheaper... One more thing. This system should be active 24/7 so i dont know if the tablet is the right choice....

I don't know your skill level so...

If you can accept using an arduino to trigger the output when sent data from the (android) tablet then half the work is already done (the arduino/android combo can both send and recieve). There is an android SDK and some details in the book 'Pro Arduino'. The arduino/android combo still has a bit of a learning curve but there are probably better books to describe it and there are lots of good ones on the arduino.