104-IIRO-8 Isolated Digital Input and Relay Output Cards

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  • 8 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
  • 8 long-life form C electro-mechanical relays switch up to 1A each
  • 8 non-isolated TTL compatible inputs

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
Last updated on November 2, 2023, 6:23 pm


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Isolated Digital Input and Relay Output Card

The 104-IIRO-8 is a low-cost card that provides isolated input and output for PC/104 Bus computer applications. The card has eight optically-isolated digital inputs for AC or DC control signals, eight TTL Inputs and eight electro-mechanical relay outputs. An Economy version can be ordered as Model 104-IIRO-8E which has no Change of State Detection or IRQs.


The isolated inputs can be driven by either AC or DC and are not polarity sensitive. Input signals are rectified by photo coupler diodes. A 1.8KΩ, ½ 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 eight 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 one group of eight form C SPDT outputs. The relays are all de-energized at power-on. Data to the relays is latched.


The I/O is accessed via a 50 pin header type.


The board is supported by most operating systems and include a free DOS, Linux and XP/2003/2008/7/8/8.1 compatible software package. This includes sample programs and source code in “C” for DOS, and Visual Basic, Delphi, and Visual C++ for Windows. Also included is a graphical setup program in Windows.


Data Sheets



Isolated Digital Inputs

  • Number of Inputs: Eight
  • 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 10KHz)
  • Isolation: 500V
  • Input Resistance: 1.8KΩ in series with an opto-coupler
  • Response Time: 4.7 milliseconds w/filter, 10 µsec w/o filter

TTL Digital Inputs

  • Number of Inputs: Eight
  • Type: TTL, 10K pull up to 5V
  • Purpose: For reading dry contact closures or any TTL compatible outputs

Relay Outputs

  • Number of Outputs: Eight
  • Type: SPDT Form C Relay – Omron G5V-1
  • Contact Ratings: 1A @ 24VDC (60VDC max), 0.5A @ 125VAC carry current
  • Contact Type: Single crossbar Ag with Au clad (bifurcated contacts optional)
  • Contact Arrangements: Channels 0-7: SPDT Form C
  • Contact Resistance: Initial, 100 mΩ maximum
  • Contact Life: Mechanical: 5 million operations minimum
  • Operating Time: 5 milliseconds maximum
  • Release Time: 5 millisecond maximum
  • Regulatory Approvals: UL and CSA


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

Power Required

  • +5VDC at 0.4A (all relays ON)


  • Ambient Temperature: Operating: -30°C to 70°C (Non-Icing)
  • Weight: Approx. 4 oz. (~115 grams)

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

ModelDescriptionPrice (USD)

Isolated Digital Input and Relay Output Card with Change of State Detect


Isolated Digital Input and Relay Output Card