8 channel USB relay board with SPST (Form A) reed relays for fast switching and high reliability, No minimum voltage or current for contact load, 200VDC/200VAC resistive 0.5A Note reed relays are typically not designed for controlling inductive loads.
Includes 8 channel opto-isolated input port on the board that can handle voltages up to 28VDC (or more with external components).
Designed for single board operation or multiple board operation by adding RS232 units to the output on the USB relay board. Up to 16 boards can be connected in a daisy chain configuration, with up to a total of 128 - 10 Amp relays under computer control, on one USB port. See example below:
AC wall adapter with DC output cable to power the board.
Compatible Accessories & Components
The information below describes the power options, (this is the voltage that powers the board itself - not the voltage/current the relays can handle).
Choose the option that best suits your application. Some options are available only on specific boards, and it depends on the type of control and the relay options for that board.
AC Wall Adapter - wall power supply that converts the AC voltage to DC to power the unit, the cable plugs into the unit with a DC power connector.
DC Terminal Block - Typically used when a regulated DC power supply with sufficient capability is already available where the unit will mount, or to power a daisy chained string of boards. Includes reverse voltage protection to prevent damage to the board if the power leads were installed backwards. Most of our boards will operate on 9-12VDC.
120V 50/60Hz - This has an on-board power supply that will operate directly off the 120VAC line voltage. The line voltage connects to a three position terminal block on the board that is marked with L1 (Line 1 -typically black), N/L2 (Neutral wire - typically white) and GND (Electrical ground - typically green or bare). Common practice is to add an inline fuse for safety.
240V 50/60Hz - This has an on-board power supply that will operate directly off the 240VAC line voltage. The line voltage connects to a three position terminal block on the board that is marked with L1 (Line 1 -typically black), N/L2 (L2 - typically red, but could be another color) and GND (Electrical ground - typically green or bare). Common practice is to add an inline fuse for safety.
Bus Power Option - This power option is only for USB boards with the Reed relays installed and specific I/O boards. The board is powered by the USB port and must be a high power port or USB port from a powered hub with a 500mA output.
Note: USB devices are also required to automatically enter ultra low-power suspend mode when the USB host is suspended, and this may turn off the power to the board and all relays will turn off that were active. Nevertheless, many USB host interfaces do not cut off the power supply to USB devices when they are suspended, it depends on the host controller. If this is a problem for your application use the USB boards that are powered by an AC adapter or DC terminal block power versions - these will not turn off the relays once set by a command (unless the power is disconnected from the board).
Daisy Chain Operation
8 Channel relay boards have the capability to daisy chain units in a string - connected to one control method (RS-232, USB, etc.) on the PC or embedded controller. Most 8 channel boards have an RS-232 output that is used to connect additional units using only one control port.
Up to 15 additional relay boards may be connected to the first unit - for a total of 128 relays under the control of one port. Each board has an individual hardware address that is set on each unit by a DIP switch. This allows control of one unit that will respond to it's address without affecting the other units on the daisy chain. All the units are hardware connected - so each unit receives the command sent to the first board almost instantly.
The first unit connected to the PC or embedded controller can be any of the control methods available. However each additional board connected to the daisy chain are RS-232 units, as shown in the drawing below: The RS-232 units may be up to 50 feet or more between units.
In addition, if only one or two more relays are required for your application, a 1 or 2 channel unit may be connected as the last board on the daisy chain to add the extra relays or if you need to add relays and I/O and a couple ISO ports to your application.
1 & 2 channel units are typically connected to only one control method, however one RS-232 board may be the last board on the daisy chain - if only a couple extra relays are needed to save cost. This board would be address "A" as this is set in firmware, and the other boards would need to be set to "B" through "P", so each board may be accessed separately.