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$56.00 (USA and Canada only)

Availability: In stock
SNAP D-Series 4-module Rack

Production Specification

The SNAP-D4M I/O mounting rack is designed for discrete control applications and can accommodate four SNAP 4-channel digital modules. The rack has an industry-standard 50-pin header connector, which allows it to be used in a variety of applications.

The logic side of the I/O circuitry can be controlled in one of several ways:
- By a Raspberry Pi®, using Opto 22’s Digital I/O Carrier Board for Raspberry Pi (part number OPTO-P1-40P)
- By a PC, using an Opto 22 PCIe-AC5 (PCI Express bus), PCI-AC5 (PCI bus) or G4AC5 or AC5 (ISA bus) PC adapter card.
- Through an Opto 22 Classic brain board, which uses one of Opto 22’s industry-standard protocols (mistic®, Optomux®, or Pamux®) to control the I/O and communicate either serially or in parallel

Field devices are wired directly to the top-mounted removable connectors on the SNAP I/O modules. The module and rack design allows modules to simply “snap” on and off the mounting rack. Use two 4-40 by ½-inch standard machine screws to secure each module in position.

All SNAP racks offer panel mounting and the option of DIN-rail mounting. SNAP racks use a single 5 VDC power source.

SNAP D Series







4-module rack

6-module rack

8-module rack

12-module rack

Power Requirements

5 VDC ± 0.25 VDC
@ 200mA max.
(700mA with brain board)

5 VDC ± 0.1 VDC
@ 300mA max.

5 VDC ± 0.1 VDC
@ 400mA max.

5 VDC ± 0.1 VDC
@ 1200mA max.

Operating Temperature Range

0 to 70 °C

0 to 70 °C

0 to 70 °C

0 to 70 °C

Relative Humidity

95%, non-condensing

95%, non-condensing

95%, non-condensing

95%, non-condensing

Length (inches)





Length (mm)





Center to Center Length





# of Center Positions






SNAP D Series Racks Data Sheet

The SNAP I/O D Series racks are designed for discrete control applications and can accommodate 4, 6, 8, or 12 SNAP 4-channel digital modules. This data sheet applies to:

Digital I/O for Raspberry Pi Selection Guide

Now you can safely and reliably sense and switch industrial-level electrical loads with your Raspberry Pi® and Opto 22 industrially hardened digital I/O.

This Selection Guide describes compatible I/O racks and modules, power supplies, and accessories that work with the Raspberry Pi and the Digital I/O Carrier Board for the Pi (OPTO-P1-40P). Specifications, dimensional drawings, and wiring diagrams for racks and I/O modules are included.

For code samples and steps to get started, also see

Using Power Supplies with Opto 22 Systems

This technical note gives an overview of power supplies for use with many Opto 22 control systems and recommends types of power supplies for Opto 22 mounting racks.

This note applies to SNAP, mistic, Optomux, Pamux, and direct I/O. It does NOT apply to groov EPIC systems, which have their own integrated power supplies. 

UL Approval Document

This document lists all Opto 22 part numbers that have the Underwriters Laboratory (UL) approval.

AutoCAD Drawings

This file contains AutoCAD drawings of Opto 22 products dating from 1988 to 2003. These are the same drawings that have been available on our BBS. Included is an Excel file describing the file names and relevant Opto 22 part numbers.

Video: Verifying Voltage at the I-O Rack

Verifying the voltage level at the I/O rack is very important for equipment safety and point value accuracy. This is the proper technique for reading the voltage level at the rack.