Opto 22 was founded in the early 1970’s by Bob Engman, who also invented the Solid State Relay (SSR). The SSR was the fore runner of Opto 22’s reliable digital IO modules and originally there were 22 products in the range of these optically isolated relays and hence the company was named, Opto 22.
The optically isolated SSR provided the ability to switch high voltage and large currents using lower DC voltages to control them. Sometimes referred to as the ‘hockey-puck’ relay, because of its shape, it provided some of the very first PC controlled high voltage/current systems.
The SSR can be described as a switch in simplistic terms but without it, modern control systems would be hard pressed to start heavy current devices such as pumps, heaters, etc. The standard hockey-puck shaped relay soon transformed into other useful variants that enable mounting on circuit boards, relay boards and the like.