Could somebody tell me if I'm asking too much from my Uno...
I'm using a 12v (500mA) power supply, which is in fact giving me 17.6v, so I'm using a voltage regulator http://www.datasheetcatalog.org/datasheet2/8/0ishsf7y9sp31h690e60g8gclc3y.pdf which give me a stable 11.94v.
Connected to the Uno I have: - SD card for data logging http://www.ebay.ca/itm/330658250543?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649 - 3 digital thermometers http://datasheets.maximintegrated.com/en/ds/DS18B20.pdf - LCD screen (2*16) running thru a shift register - clock http://www.ebay.ca/itm/170794823401?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649 - 12v relay to activate 2 pc fans. Those fan run directly from the voltage regulator - 120v relay to activate a bigger fan http://www.datasheetdir.com/VB-6TCU-E+download
When I'm running the Uno thru the USB port power, everything works fine (the LCD screen is a little dimmer) and no overheating (perfectly cold to the touch. But as soon as I modify the circuit and put the 11.94v in the Vin and GND, then the board start overheating (very hot to the touch).
Thanks for your help.