• USB-RS232-I2C-SPI-8VI8SRMx-2

8 Signal Relay, 8 Wide Voltage Input, Multi-Protocol card


USB, I2C/SPI communications and RS232 communications

Communications data activity LEDs

3 communications inputs can exist at the same time.

8 3A, 120V Opto-isolated signal replays + individual LEDs

8 Opto-isolated, wide input voltage sensors + individual LEDs. Max input 60V AC or DC.

On board regulator with 7V to 24V input.

Same board outline as USB8PR

2 part horizontal connectors

8 bit 5V logic DIO

8 bit 3V3 logic DIO on the I2C interface

Optional bespoke software


General purpose relay card with 8 opto-isolated, 120V, 3A signal relays and 8 3V to 60V, AC/DC, opto-isolated voltage sensing inputs.

This card has 4 communication options:





This card also has 3 powering options:

USB power

External 5V DC with reverse polarity protection.

External 7 to 24V DC with reverse polarity protection and regulated 5V output on the external 5V terminal for powering your own hardware. See detailed Power Supply description below.

Two LEDs indicate data transfers between your control hardware and the relay card for help with debugging and testing.

Each relay channel or voltage sensing input has its own LED to indicate status.

The card has been designed with future expansion in mind including access to 8, 5V DIO channels connected to the main controller and a further 8 3V3 DIO channels connected to the I2C/SPI port if this option is fitted. The programming pins for the control processor are also available to enable re-purposing of the card by loading application specific software.

The card is RoHS compliant and CE marked.

Product Datasheet 53

Product Datasheet 56

You can order any of our boards with customisations or without connectors fitted - contact us for prices

'Pre-Order' simply means that we will build to order. Delays are minimised - with most orders dispatched within 48 hours. More time is needed if we have limited PCB stock. If you require clarification of timings, please phone or email us. 

EasyDAQ is primarily a business-to business seller, supplying products around the world, therefore advertised prices exclude VAT. Customers in the UK and Northern Ireland will be charged VAT  at checkout. 


Power supply

USB or external 5V powered (up to 8 relays @ 40mA per relay).

External 7V – 24V switch-mode 6W maximum input power. Up to 500mA at 5V DC available to the user’s hardware from the 5V terminal.

Control Interfaces

USB 1, 2 or 3, Type B connector, hot pluggable.

RS232 9 way D female.

I2C or SPI on a JST XH 8pin header.

Operating temp range

-20 to +800C


Rated voltage/current

5VDC/42mA each

Must operate/release voltage

75%/10% of rated voltage

Maximum contact ratings

1A/120VAC or 1A 30VDC

Minimum recommended contact rating

5V @ 20mA

Contact resistance

100mΩ max

Operate/release time


Contact bounce period

0.6mS operate/ 7.2mS release

Contact material


Operational life (min)

Mechanical 107 / Electrical 105

Contact arrangement

SPDT, Form C

Command format

The card is commanded via simple single ASCII characters (+ status byte). I.e a 2 byte pair. These are commands that address each port of the PIC processor device (Hex equivalent shown in brackets). The card can be controlled using a Terminal emulator if connected via USB or RS232– see below.

It is important to include a 20ms processing delay between command pairs.

Port B (Channels 1-8) Relay commands:

ASCII ‘B’ (42H), X Initialises the card (sets the port & channel I/O directions). Set direction of Port B, 1=Input, 0= output. (i.e. where X=10111111 (AFH) = sets bit 7 as an output, the rest as inputs).

ASCII ‘C’ (43H), X Write data X to Port B (i.e. X=00000001 (01H), sets channel 1 to active). Valid data bytes are latched by the card until a further valid data byte is written to it.

Example: To set all Port B to output for controlling the relays and switch on relays 1 and 4:

The first byte pair initialises the port to all output and the second and subsequent byte pairs are then used to control the relays. The 8 bits of the data byte represent the relays to be controlled. Relay 1 is controlled by Bit 0, relay 2 is controlled by Bit 1 and so on to relay 8 being controlled by Bit 7.

Port C (Channels 9-16) Input commands:

ASCII ‘E’ (45H), X Initialises the card (sets the port & channel I/O directions).

The card will be set to input on power up so initialising this port is not necessary.

ASCII ‘D’ (44H), X Read Port C data.

This is a two byte command with the second byte being any value and is ignored. The data byte will be transmitted after the dummy byte has been received.

Port D (Channels 17-24) DIO commands:

ASCII ‘H’ (48H), X Initialises the card (sets the port & channel I/O directions). Set directions of individual bits of Port D

ASCII ‘K’ (4AH), X Write data X to Port D (i.e. X=00000001 (01H), sets channel 17 to input and the rest to output).

ASCII ‘G’ (47H), X Read Port D. X is a dummy value. The data byte is returned after the dummy byte has been received.

Serial Port settings

For the RS232 and the USB interfaces the controlling system must be set to:

Baud rate: 9600

Parity: 0

Data: 8 bits

Stop bits: 1

Handshaking: None

Auto detection & com port assignment

When you connect this card to a USB port of your computer for the first time, it will be auto-detected and ask you to install drivers (downloadable from the ‘downloads’ section of our website). After installation, the card will appear as a ‘virtual’ COM port and be automatically assigned a COM port number by your OS. Following installation, the COM port number can be manually re-assigned via the control panel if required. Following reboots or disconnects of the USB card, the same COM port number will be assigned.

Using a Terminal Emulator

In order to test operation, the card can be connected to a serial port and controlled from a terminal emulator program such as “PuTTY” or “Realterm”. See our “Data Sheet 50 (Using Terminal Emulators to control and test EasyDAQ cards)”. Ensure port configuration is set as shown above, type (ASCII) characters shown above to achieve port direction and read or write command/data.

I2C/SPI control

If the I2C/SPI option is fitted then the card can be controlled directly fom another processor such as an Arduino, Raspberry Pi, BeagleBone etc.

The communications via the I2C or SPI are managed by a NXP SC16IS750 I2C/SPI to serial converter.

The SC15IS70 needs to be set up by the controlling system to enable communications with the processor on the relay card.

The following is an excerpt from an Arduino program that uses the “Wire.h” library to set up I2C communications:

#include <Wire.h>

byte Address = 0x48; // Address of the SC16IS750 when A0 and A1 are pulled high.

// The value in the datasheet has to be shifter right by 1 bit to allow for

// the R/W bit.

int delaytime = 20; // 20ms minimum delay between instructions

// Register addresses shifted left 3 bits into bits 3:6. See NXP SC16IS740/750/760 datasheet Rev. 7 — 9 June 2011 section 10.4 "Use of subaddresses"

// SC16IS750 Registers :

#define THR 0x00 << 3 // Transmit Holding Register. Can only be written to.

#define RHR 0x00 << 3 // Receive Holding Register. Can only be read from.

#define IER 0x01 << 3

#define FCR 0x02 << 3

#define IIR 0x02 << 3

#define LCR 0x03 << 3 // Line Control Register

#define MCR 0x04 << 3 // Modem Control Register

#define LSR 0x05 << 3

#define MSR 0x06 << 3

#define SPR 0x07 << 3 // Scratch Pad Register

#define TXLVL 0x08 << 3 // Transmitter FIFO Level register (TXLVL) address (0x08)

#define RXLVL 0x09 << 3

#define DLAB 0x80 << 3

#define IODIR 0x0A << 3

#define IOSTATE 0x0B << 3

#define IOINTMSK 0x0C << 3

#define IOControl 0x0e << 3 // I/O Control register

#define EFCR 0x0f << 3 // Extra Features Control Register

#define DLL 0x00 << 3

#define DLH 0x01 << 3

#define EFR 0x02 << 3 // Enhanced Features Register

#define XON1 0x04 << 3

#define XON2 0x05 << 3

#define XOFF1 0x06 << 3

#define XOFF2 0x07 << 3

void setup() {

Wire.begin(); // join i2c bus (address optional for master)

setupBRG(); //

// rest of your setup here


void setupBRG(){

putByte(IOControl,B00010000); // Software reset


putByte(LCR,0x80); // divisor latch enable

putByte(DLL,12); // Lower byte of BRG ((1.8432MHz/(12x16)). 16 clocks required per bit sent

putByte(DLH,0x00); // Upper byte of BRG ((1.8432MHz/(12x16)). 16 clocks required per bit sent

putByte(LCR,0xBF); // Access EFR register

putByte(EFR,0x10); // Enable Enhanced functions

putByte(LCR,0x03); // Setup LCR for normal operation: 8 bit data, 1 stop bits, no parity

putByte(FCR,0x06); // Reset FIFOs

putByte(FCR,0x01); // Enable FIFOs

Serial.println("BRG set up");



void putByte(byte reg, byte data){

Wire.beginTransmission(Address); // transmit to device

Wire.write(reg); // sends the register address

Wire.write(data; // Setup LCR for normal operation: 8 bit data, 2 stop bits,

// no parity

Wire.endTransmission(); // stop transmitting


Complete examples can be found on the download page of our website.

Detailed electrical specification of inputs:

This card has opto-coupled, wide voltage range, current limited, AC or DC inputs.

Each input pair is individually electrically isolated.

Input specification




Max input voltage

60V DC or AC Peak

Download datasheet

Operational Parameters
Manufacturer EASYDAQ
Control Interface USB, RS232, SPI, I2C
Relay coil voltage 5V
Relay contact current 1A
Digital input channels 8
Relay Type SIGNAL
Wide Input Voltage YES

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  • Brand: Easydaq
  • Product Code: USB-RS232-I2C-SPI-8VI8SRMx-2
  • Availability: Pre-Order
  • £120.00

  • 10 or more £108.00

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Tags: SIGNAL, USB, SPI, I2C, RS232, Wide input, 2 part connectors, wide input voltage, USB 8 relay, relay board, USB-RS232-I2C-SPI-8VI8SRMx-2, Free shipping, EasyDAQ, UK