CM3-Home - Home Automation board for Raspberry Compute module 3

CM3-Home is a mother board designed around the Raspberry Pi Compute Module 3 to provide reliable and long-term available hardware for Home Automation open source applications like OpenHAB, Home Assistant, etc. The board has been designed to provide a wide set of commonly used wired bus and installed inside a DIN rail switchboard.

The CM3-Home board will be presented for the first time at Maker Faire Rome 2017 - December 1-3, 2017.

Hardware secifications

On the CM3-Home mother board we have integrated the following interfaces:

  • 2 opto-isolated RS485
  • 1 TTL level serial port for system console
  • 1 TTL level serial port for external microcontroller
  • 1 1-wire bus
  • 2 I2C buses for Seedstudio Grove module
  • 2 low power relays
  • 2 opto-isolated dry contact inputs
  • 2 ADC inputs for resistor balance tampered sensors
  • 1 opto-isolated twisted pair bus electrically compatible KNX bus
  • 1 opto-isolated twisted pait bus electrically compatible with DALI bus
  • 1 ISM radio module at 868 MHz with a Cortex M0+ fully available for customer application (http://www.acmesystems.it/yarm)
  • 1 WiFi 2.4 GHz (enabled for access point mode)
  • 1 Ethernet port 10/100Mbit
  • 1 Stereo audio out
  • 1 IR remote receiver at 38KHz
  • 2 USB 2.0 host ports
  • 1 SPI/GPIO port for small TFT LCD display modules
  • 1 MIPI connector for Raspberry CAM

The Raspberry PI Compute Module 3

The CM3-home is a motherboard for the OEM market designed around a Raspberry Pi Compute Module 3 which is the production-friendly version of most the popular Raspberry Pi 3 single board computer.

Like the Raspberry Pi 3, this module comes with a Broadcom BCM2837 Microprocessor, 1.2GHz clock and 1GByte of RAM memory and is fully compatible with it, but its availability has been going on for years to ensure the continuity of industrial productions that make use of it.

As written in the official module datasheet: " Raspberry Pi guarantee availability of CM3 and CM3 Lite until at least January 2023 ".

The CM3-Home market

As like as the Raspberry Compute Module 3 also the CM3-Home mother board is suitable for the business to business market. On this site it is possible to buy the empty CM3-Home mother board as single piece or in bulk packages of 10-50-100 etc pcs or even just the PCB. For MOQ of 1000 pcs it is also possible to order the PCB in any color or with a custom silk screen.

The typical customers of this board are:

  • System Integrators that want to create and resell their own Home Automation solution based on the Open Source software available on Internet,
  • Makers that want to create their own software on a reliable platform
  • Resellers that just want to create a Home Automation kit to add to their catalog adding the CM3 module and all the accessories to maximize the gain.

Acme Systems will not provide ready-to-use microSDs or support to install popular software on this mother board but just the basic info about the small differences between the standard Raspberry Pi 3 and the CM3-Home/Raspberry CM3 to understand how to use them with standard software.

CM3-Home internal architecture

Twisted pair bus

A Siemens TP-UART-2 is integrated on-board to provide an electrically isolated bus compatible with some commercial KNX devices.

CM3-Home is not a certificated KNX device so we can't warranty the fully functionality with all the KNX devices.

The CM3-Home doesn't provide the bus power supply so an external KNX power supply is requested to operate. The TP-BUS signals are available on two screw terminals. Detailed info on how to integrate the KNX bus with Raspberry Pi is available on this link.

How to use the TT-BUS

The TP-UART-2 is wired on the serial port /dev/ttyAMA0 and is compatible with the open source software knxd (https://github.com/knxd/knxd).

Light bus

This is another type of twisted pair bus electrically compatible with some commercial DALI devices.

CM3-Home is not a certificated DALI device so we can't warranty the fully functionality with all the DALI devices.

The bus is opto-isolated from the CPU side but is in common "electrical domain" with the RS485 and the dry contact inputs.

The data bus power supply is provided by the CM3-Home so up to 16 devices is not required an external power supply. The Light bus is managed in GPIO bit banging. More info is available on this link.

RS485 buses

Two separated RS485 buses are available on 6 screw terminals.

The signal are A, B and GND and are opto isolated from the CPU side. The buses are not opto-isolated between them. They are in the same "electrical domain" of the dry contact inputs and light bus interface.

Through this bus you can connect DMX512, Modbus and other generic RS485 devices using the serial lines on /dev/ttyUSB0 and /dev/ttyUSB2 provided by the FT4232 chip.

Seedstudio Grove modules

Grove is a modular, standardized connector prototyping system made by the company Seeed studio.

On the CM3-Home board are available 2 Grove connectors compatible with the 3.3 volt level I2C and GPIO Grove modules:

  • the left side connector is managed by a Cortex M0+ microprocessor and can be managed using Arduino code.
  • the center side connector is managed directly by the Raspberry Pi I2C bus and can be managed using Raspberry Pi code.

Dry contacts

Two dry contacts inputs with a common line is on 3 screw terminals.

This lines are opto-isolated from the CPU side and are in the same "electrical domain" of the RS485 and light bus interface.

The line status are read trought 2 GPIO line on Raspberry Pi.

Relays

ADC inputs

Serial

USB ports

ISM Radio module and Cortex M0+

LAN and WiFi

Stereo audio out and camera interface

Infrared remote control

Board versions available

The board will be available in two versions.

CM3-Home lite edition
This is a cheap version with the basic interface suitable for the most part of residential installations
CM3-Home full edition
This is a full featured version compatible with some commercial lighting systems and some energy harvesting Radio ISM nodes.

These main differences between these two version are:

Hardware description CM3-Home full CM3-Home lite
Vertical Sodimm socket for Raspberry Pi Compute Module 3 yes yes
Vertical socket for microSD yes yes
Microchip LAN9514 chip yes yes
USB 2.0 host ports 2 2
LAN 10/100Mbit 1 1
WiFi module 2.4GHz yes optional
FTDI FT4232 chip (4 serial ports from a single USB) yes yes
Stereo audio out on 3.5 mm jack yes yes
MIPI camera connector for standard Raspberry Camera yes yes
Serial debug port @ 3.3 volt on strip yes yes
Generic serial port @ 3.3 volt on screw terminal yes yes
Low voltage relay contact 2 2
Clear contact inputs on screw terminal 2 isolated 2 not-isolated
IR receiver @ 38KHz yes optional
Seeedstudio Grove connector 2 1
Power-in 12-24VDC 12-24VDC
RS485 on screw terminal 2 isolated 1 not-isolated
Internal connector for 2.2 inch SPI TFT display (320x256) with resistive touch yes optional
1-Wire bus on screw terminal 1 1
Siemens TP-UART chip for twisted pair commercial home automation bus yes
Isolated DC/DC converter 2
Light bus for commercial dimmerable ballast on screw terminal yes
Yarm radio module (Yarm) (Microchip SAMD21 + ATA8510) yes
ADC lines on screw terminal 2

Enclosure

CM3-HOME board has been designed to be enclosed inside a 9 module DIN RAIL case made by ELBag:

http://www.elbag.net/9k_I.html

Schematics