Isolated Digital Input and Relay Output Card


  • 16 optically-isolated, non-polarized CMOS compatible digital inputs accept 31VDC or AC rms
  • IRQ on input change of state (COS) eliminates the need for constant polling
  • Slow/fast filter to accommodate AC voltages and noisy DC inputs
  • 16 long-life form C electro-mechanical relays switch up to 1A each

Factory Options: (call for pricing and availability)

  • Economy version without COS feature
  • Input only and relay only versions
  • Expanded input voltage levels
  • RoHS Available. Please contact us for ordering information
The 104-IIRO-16 is a low-cost board that provides isolated input and output for PC/104 Bus computer applications. The board has sixteen optically-isolated digital inputs for AC or DC control signals and sixteen electro-mechanical relay outputs. The Change of State Detection capability of ACCES' Model 104-IIRO-16 sets this board apart from the competition. An Economy version can be ordered as Model 104-IIRO-16E which has no Change of State Detection or IRQs. Also available is Model 104-RO-16 which has 16 relay outputs only.


The isolated inputs can be driven by either AC or DC and are not polarity sensitive. Input signals are rectified by opto-coupler diodes. A 1.8KΩ, Watt resistor in series provides current limiting. The input voltage range is 3V to 28V (rms). To extend the input voltage range, you may connect external resistors in series with the input.

Each input circuit is switch selectable for slow/fast filter that has a 4.7 millisecond time constant. The filter must be selected for AC inputs in order to eliminate response to AC noise. The filter is also valuable for use with slow DC input signals in a noisy environment. The filter may be switched out for DC inputs in order to obtain faster response. Filters are manually switched individually on or off.


Interrupts are enabled/disabled by software. When the change-of-state detection circuit is enabled, the card asserts an interrupt whenever any of the sixteen isolated inputs change state. Once an interrupt has been generated and serviced, it is automatically cleared. This feature greatly frees up system resources by eliminating the need for constant polling to see when an input has changed state.


The electro-mechanical relay outputs are comprised of two groups of eight form C SPDT outputs.


The relay outputs are accessed via a 50 pin header type connector, while the isolated inputs are accessed via a 34 pin type header connector.


104-IIRO-16 utility software provided on CD includes sample programs in a variety of languages for DOS / Windows XP -> 10, both 32 & 64 bit. A Windows graphical setup program is also provided, and a "C" language sample for Linux.

Drivers and Downloads

List of available Downloads: Software Packages, Drivers, Manuals, and other documents

Custom Software

ACCES also offers Custom Software Services for our products. Our prices are unbelievably low, often as inexpensive as free! If you need something tweaked to support your needs, or an entire enterprise application developed from scratch, it is definitely worth your time to inquire with us, first.

Available Reference Manuals

Available Software Downloads

Available Datasheets

Further information about available ACCES Software:

Redistributing Windows Drivers
A list of ACCES drivers and the files that compose them under different versions of Windows, so you can easily redistribute ACCES cards and drivers.


Isolated Digital Inputs

  • Number of Inputs: Sixteen
  • Type: Non-polarized, optically-isolated from each other and from the computer. (CMOS compatible).
  • Voltage Range: 3 to 31V DC or AC RMS (50 to 10 KHz)
  • Isolation: 500V
  • Input Resistance: 1.8KΩ in series with opto-coupler.
  • Response Time: 4.7 milliseconds w/filter, 10usec w/o filter

Electromechanical Relay Outputs

  • Number of outputs: Four SPDT form C
  • Contact Type: Single crossbar; Ag with Au clad
  • Carry Current: 2A
  • Rated Load AC: 0.5 A at 125 VAC (62.5 VA max )
  • Rated Load DC: 1 A at 24 VDC ( 30 W max )
  • Switch Voltage / Current: 125 VAC; 60 VDC / @ 1A (max)
  • Contact Resistance: 100 mΩ max
  • Max. Switching Voltage: 125 VA, 60 VDC
  • Max. Switching Current: 1A
  • Max. Carrying Current: 2A
  • Contact Life-mechanical: 5,000,000 operations min
  • Operating / Release Time: 5 ms max (mean value: approx 2.5 ms, and 0.9 ms respectively)


  • When enabled by software, interrupts are generated when any digital input changes state (High to Low or Low to High, and from signal to no signal with AC inputs).

Power Required

  • +5VDC at 0.5A (all relays ON).


  • Ambient Temperature: Operating: -30°C to 70°C. (non-icing)
  • Weight: Approx. 4.5 oz. (~130 grams).

CE testing & approval must be done at the system level, in the designed enclosure, and is not done on individual boards.

ModelPrice (USD)

Acquisition, Control, Communication: Engineering and Systems

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