Diamond Systems PMM-P 16-Channel SPDT (Form C) Relay Output PC/104 Module

Switching lamps, solenoids, contactors and alarms from a PC/104 stack calls for real relay contacts rather than logic outputs. The PMM-P is the Pearl-MM module from Diamond Systems, a PC/104 industrial control board with 16 relays, designed so a host can switch AC and DC loads from software while keeping them isolated from its own circuitry.

Control is deliberately simple. Two 8-bit I/O registers drive the relays, one bit per relay: writing 1 turns a relay on and writing 0 turns it off. On power-up or reset every bit is 0, so all relays are off with common connected to normally closed, a predictable state for safety and reliability. Relays operate or release in 4 ms maximum.

The relays are SPDT Form C, each with common, normally open and normally closed contacts, switching up to 125 V AC at 0.5 A resistive, with switching power of 60 W DC or 60 VA AC, contact resistance of 100 mΩ maximum and a rated life of 100,000,000 operations. Isolation is 500 V DC or AC both channel to channel and channel to board. Two 50-position pin headers carry all I/O, one for relays 0 to 7 and one for relays 8 to 15, using one or two C-50-18 cables. The OPMM-1616-XT adds 16 optoisolated inputs to 16 relays, and the IR104-PBF pairs 20 inputs with 20 SPST relays on screw terminals.

The PMM-P runs on +5 V and operates from -40 to 85 °C at 5 to 95% non-condensing humidity, and Diamond quotes an MTBF of 118,227 hours. It stacks with PC/104 hosts such as the HELIX SBCs, and the GPIO-MM-XT series adds TTL digital lines and counters where a stack needs both.