There are 3 kinds of control units - SM2-xxx, SM3-xxx and xxx-Basic-xx.
SM2 is a design from 2012 and under normal circumstances it ceases to be manufactured after 10 years. Due to the chip crisis, we still produce these units if we can get the processors (chips) that are used in them.
SM3 is a new successor, developed in 2018-2020 with a faster processor, larger flash memory for code, larger and faster RAM, faster SD card data transfers, more reliable Ethernet PHY, with added surge protection on Ethernet and added differential +- 10V analog input.
Basic units are cost-effective, they are intended for smaller systems without capability to add GPRS / NB-IoT modem, other extension modules and with no interface for sensors.
Extension modules complement the functionality of the Solar Monitor Main Unit. Place the expansion module on the DIN rail next to Solar Monitor or another expansion module and simply pull up to him. Using hidden bus in DIN rail is so very quickly connected without wiring.