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Four Relays four HV Inputs 8-Layer Stackable HAT for Raspberry Pi

SKU: SM-I-010

Regular price $45.00


  • Four Relays 4 HV Inputs 8-Layer Stackable HAT for Raspberry Pi
  • Status LEDs and NO/NC contacts
  • Switch loads of up to 8A and 240VAC/24VDC
  • Four high voltage opto-isolated inputs with status LEDs
  • Separate connectors for low (3V-24V) and high (48-240V) inputs
  • Universal inputs reading AC or DC signals
  • Eight layer stackable to 32 relays and 32 inputs
  • RS485 port
  • Raspberry Pi reset push button
  • Pluggable Connectors 30-16 AWG wires
  • Uses only I2C port (address 0x15..0x0e), all GPIO pins available
  • Four Relays Raspberry Pi
  • Works with any Raspberry Pi from ZERO to 5
  • ECCN Code EAR99
  • Command Line
  • Python Drivers
  • Node-Red node and examples
  • OpenPLC module
  • Arduino Library


The 4.0 release of the card replaced the I/O expander with a local processor. This enhancement allowed us to add several new features:

  • Independent RS485 (no Raspberry Pi needed)
  • MODBUS protocol allows the card to be controlled from any PLC
  • Transition counters to 4kHz on all inputs
  • Input counters with cumulative or PPS (pulse per second) reading up to 4kHz
  • 2 x Quadrature encoder inputs reading up to 4000 PPS
  • PWM inputs on each channel, reading both the fill factor and the frequency


Four Heavy Duty Relays plus Four High Voltage Inputs for Raspberry Pi

Drive 8A/240VAC loads and read 3V to 240V, AC or DC, opto-isolated inputs for all your Home or Industrial Automation Projects

Perfect add-on to your project when you have to control large number of heavy-duty AC loads and/or you have to read wide range inputs. Stackable to 8 layers, the card can add up to 32 relays to each Raspberry Pi in a very compact form factor. In addition, you can read up to 32 opto-isolated inputs.

Pluggable connectors make the 4-RELAYS card easy to use when multiple cards are stacked up.  All relays have Normal Open and Normal Close contacts and can switch up to 8A/240VAC. 

The optically isolated universal inputs can read AC or DC signals from 3V to 48V. The input connectors have a low voltage port which can read signals between 3V and 24V, and a high voltage port which can read signals between 24V and 48V.


The card is compatible with all Raspberry Pi versions from Zero to 5. All stacked cards share the I2C bus using only two of the Raspberry Pi’s GPIO pins to manage all eight cards.  This feature leaves the remaining 24 GPIOs available for the user.


The card needs 5V to operate and can be powered from Raspberry Pi or from it's own 2 pin pluggable connector. The relay coils are also powered from the 5V.  The card draws 10mA with all relays off. Each relay needs about 80 mA to turn on. If power is applied to the 2 pin pluggable connector, no other power supply is needed for the Raspberry Pi.


Up to eight cards can be stacked on your Raspberry Pi. Each card is identified by jumpers you install to indicate the level in the stack. Cards can be installed in any order. A three position jumper selects the stack level.

Stack Level Jumpers

For your convenience, two jumpers are provided with each card. 


The board is protected to accidental reverse power supply with a 5.8A, 39 mOhm MOSFET which breaks the ground line if reverse power is applied. 


Shutting down the Raspberry Pi by turning off the power can result in SD Card failure. To prevent this, a shutdown command needs to be used before power cut-off. But this requires a monitor, keyboard and mouse connected to the Pi. 

A momentary on push button installed at the edge of the board provides a convenient way to shut down the Raspberry Pi. The button is read by the local processor, which can be programmed to signal the Raspberry Pi by setting low pin 37 of the Raspberry Pi GPIO connector (GPIO26). You can also read the status of the pushbutton from the I2C interface. You need to write a script which monitors this pin, and if pressed for more than a desired time, issues the shut-down command.


4-RELAYS 4-INPUTS Card Layout


  • Power Supply: 5V/8A pluggable connector with reverse polarity protection
  • On board resettable fuse: 3A
  • Opto-isolated Digital Inputs:
    • Input Forward Current: Typical 5 mA, maximum 50 mA
    • Low Voltage Input Series Resistor: 2.2K
    • High Voltage Input Series Resistor: 120K
    • Isolation Resistance: Minimum 1012 Ω
  • Relays: NO/NC contacts, 8A/240 VAC-24 VDC


4-Relays 4-Inputs Card Mechanical Specifications


The card can be tested before installation by running a simple command from the command line. The card will cycle each relay on and off at 0.5 seconds interval. The clacking noise of the relays and the lighting of the LEDs will assure that all relays are functioning.

RS485/MODBUS port

A standard RS485 transceiver permits the Raspberry Pi to communicate using any protocol including MODBUS, PROFIBUS, camera PTZ control, etc. The transceiver can be driven either from the Raspberry Pi serial port, or directly from the local processor. Install the jumpers 485-TX and 485-RX on connector J3 to drive the port from Raspberry Pi. Install the terminator jumper 485-TERM if the card is last on the RS485 chain.


  • Transition counters to 4kHz on all inputs
  • Input counters with cumulative or PPS (pulse per second) reading up to 4kHz
  • 2 x Quadrature encoder inputs reading up to 4000 PPS
  • PWM inputs on each channel, reading both the fill factor and the frequency
  • 1% resolution on PWM inputs up to 100Hz, 5% resolution up to 500Hz.





You can write your own application using the Command Line or Python Libraries provided. Usage example for the python library can be found in file on repository. No programming is required if you use the Node-Red nodes we supply. You can drag-and-drop the functional blocks to design your application. Examples are also provided.



    The card can be installed parallel on a DIN-Rail using the DIN-Rail Kit Type 1, or perpendicular using the DIN-Rail Kit Type 2.


    When you purchase the Four Relays Card you will receive the following items:

    1. 4-RELAYS add-on HAT for Raspberry Pi

      4-RELAYS/4-INPUTS for Raspberry Pi

      2. Mounting hardware

      • Four M2.5x18mm male-female brass standoffs
      • Four M2.5x5mm brass screws
      • Four M2.5 brass nuts
      Mounting Hardware

      3. Two jumpers

      Stack Level Jumpers

      4. Mating connector plugs

      4-RELAYS/4-INPUTS connector plugs


      1. Plug your 4-RELAYS 4-INPUTS card on top of your Raspberry Pi and power up the system.
      2. Enable I2C communication on Raspberry Pi using raspi-config.
      3. Install the card software from
      • ~$ git clone
      • ~$ cd /home/pi/4rel4in-rpi
      • ~/4rel4in-rpi$ sudo make install
      • ~/4rel4in-rpi$ 4rel4in

      The program will respond with a list of available commands.

      Customer Reviews

      Based on 5 reviews
      Rich set of features for a very reasonable price

      Using the card on the RS485 port, no Raspberry Pi. MODBUS commands from a standard PLC, read inputs and set relays as expected. Great HAT

      D Scholl
      Good combination of inputs and outputs

      The card works as expected. We plan to use the inputs to read the relay outputs, as a super-redundant system to make sure the relay contacts are working.

      Antonio Colmenarez
      Works right away...

      Documentation was good. Testing with the comnands did it so well, that I decided to develop my solution with popen()...

      In no time, my solution had 4 working relays and 4 wirking inputs...

      Charles McQuade
      Love this board

      I needed a way to get the status of my gate that is about 300m away from my house. I have network down there so I put in a PI with this board and am able to know when the gate is open or closed. I plan to use some of the relays for controlling lighting down the road. Put it in, has not missed a beat since I brought online. Sending the gate status out over MQTT. The company is always there if I need support.

      Great Product.

      highly recommanded

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