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Meduino Mega2560 Pro Mini
The Arduino board called Mega2560 uses the ATmega2560 microcontroller. The Arduino board costs 35 EURO. The microcontroller is very interesting, it contains a lot of analog(16) inputs and digital inputs/outputs (54, 15 for PWM) and the microcontroller is working on 5V voltage.

Epalsite electronics designed the small board exactly with this microcontroller. You can buy it e.g. on ebay.com for 12.99 USD. The Meduino Mega2560 Pro Mini board.

Do you know the specification of ATmega2560? Short spec:
DC Current per I/O Pin - 40 mA
DC Current for 3.3V Pin - 50 mA
Flash Memory - 256 KB of which 8 KB used by bootloader
SRAM - 8 KB
EEPROM - 4 KB
Clock Speed - 16 MHz

The spec of Meduino ATmega2560 Pro Mini:
Completely compatible with original Arduino Mega2560
Pin pitch: 0.1 inch
Size: 5.42cm*3.68cm
With Atmega16U2 chip as the USB to Serial converter
Working voltage: 5V
Input Voltage: 7-12V
Analog Input Pins: 16
Digital I/O pins: 54
The maximal current from 3.3V regulator: 150 mA

The ebay link https://www.ebay.com/itm/New-Small-Meduino-Mega2560-R3-Pro-Mini-ATMEGA16U2-Arduino-Mega2560-Compatible/162593120251

Homepage of board http://wiki.epalsite.com/index.php?title=Mega2560_Pro_Mini