Sequent Microsystems designs and manufactures I/O expansion cards for Raspberry Pi. These cards enhance the functionality of Raspberry Pi by providing analog inputs and outputs (0-3.3V, 0-10V, 4-20mA), optically isolated inputs supporting 3-240V AC/DC, 4 to 16 onboard relays and solid-state outputs, event counters, quadrature encoders, 1K/10K thermistor interfaces, RTD sensor inputs, battery-backed real-time clocks, RS485/MODBUS communication, as well as MOSFET and TRIAC load drivers. All cards utilize only the I2C interface to communicate with Raspberry Pi, leaving all GPIO pins available for other applications.