Sequent Microsystems designs and manufactures I/O Cards for Raspberry Pi. They expand the capabilities of Raspberry Pi with analog inputs and outputs (0-3.3V, 0-10V, 4-20mA), optically isolated inputs from 3 to 240V AC or DC, 4 to 16 on-board relays and solid state outputs, event counters, quadrature encoders, 1K/10K thermistors, RTD sensor inputs, Real Time Clock with battery backup, RS485/MODBUS communication, MOSFET and TRIAC load drivers. All their cards use only the I2C port for communicating with Raspberry Pi, leaving all the GPIO pins available for other tasks.