Good morning Adi, thank you for helping me. The voltage signal (low voltage) comes from the telluric ground with different PH. I will put two probes in the ground to acquire the voltage (I need a resolution of at least 50 mvolts). The voltage, converted to digital signal, should be acquired by the wireless node. Because I need in the same region to acquire temperature and moisture too, I was thinking to use the microchip MCP3208 whose output should go to a network processor (node) such as the CC2480 (ZigBee protocol). What do you think about ? First of all I need an high impedance circuit to implement the voltmeter....