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The KTA-223 Relay Board is a USB or RS485 controlled module that can interface a PC to eight or more SPDT relays. This could be very useful for controlling real world devices - such as lights and sprinkler systems - and reading sensors or monitoring switches and other digital signals.

The controller is based on the hardware of the extremely popular Arduino platform. It can be programmed as a stand-alone controller using the free, open source Arduino environment. Internally, the controller is “shield-compatible”, allowing the use of many extension boards designed for the Arduino Deumilanove.

The on-board relays are capable of switching up to 5A at 250VAC, 10A at 120VAC and 10A at 24VDC, but the PCB traces can only handle up to about 5A.

With the default firmware, a simple ASCII protocol allows control from Windows/Mac/Linux using either USB Virtual COM drivers or RS485. Additionally, multiple devices can be connected to one RS485 bus, allowing control of many devices from one USB port.

A large number of mating screw terminals are included with this product. USB cable not included.

Note: To get this to work with the R3 version of the Arduino Ethernet shield you will need to connect Pin 1 of the ICSP header to D12, Pin 3 to D13 and Pin4 to D11.


  • 8 Relay Outputs 5A 250VAC
  • 4 Opto-Isolated Inputs 5-30VDC
  • 3 Analog Inputs (10 bit)
  • Connections via Pluggable Screw Terminals
  • 0-5V or 0-20mA Analog Inputs, Jumper Selectable
  • 5A Relay Switching
  • Power Indicator LED
  • All enclosed in Professional looking plastic case
  • Arduino Compatible
  • Accepts Arduino Shields (Ethernet / XBee)
  • USB Virtual COM or RS485 Input
  • Easily connect multiple units far apart by RS485
  • Updated firmware - fixes a bug with the Relay Status command (status of wrong relay was reported)


The KTA-223 USB/RS485 Relay IO Board appears in the following collections:

SKU SF-DEV-09526