Category Archives: Home Automation

New Micro PLC Backbone

My previous backbone board had to little space between connectors + no connection for PSU & communication – this one has 10mm between connectors which is more realistic – thought I still expect one Add-On board to use ca 20mm width. The total width “as is” is 100mm, so it is still very small.

I actually need to find a solution on the mechanical boxing before I finish this one + this is still only an idea draft that need to mature. I probably should add bias and terminator for RS485 on the backbone. Have some spare space on right.

As for add-on boards I am toying around with the following ideas;

  • An Ethernet connectivity board.
  • An RS-X connectivity board.
  • An Raspberry PI connectivity board.
  • An analogue input board.
  • A PWM channel board.
  • A camera input board.
  • A voice & mic board.
  • A DC-/Stepper- Motor board.
  • A 3-Phase motor board.
  • A GSM/3G/4G Board.

We can have a lot of fun here, but I will let these ideas mature a bit…

Micro PLC Backbone

Just an update on the backbone board. I have decided to use a “All-In-One” central for home automation, but I still want to make a minimized PLC alike system. This backbone is very small – only 50mm width and 65mm height. The connectors are basically so tight with only ca 6.3mm apart that we are not likely to use every slot. I considered making it larger, but decided against it because the primary target here is mobile robotics. The connectors give me the option to use 1, 2, 3, 4 or even more slot width on a single card + I can add backbone board by having a board to board cable.

The main difference is that I ditched the A and B PSU signals and use a wider, combined lane to increase available ampere. I also add drill holes for each board. I am still a bit undecided about how I connect this to the PSU etc. I will be back on that.

This last picture illustrate the new power lanes. Wide tracks on both sides to support higher currents. The weak point is however how to connect this to a PSU. At present I would use a 40 pin connector and 4 cables per voltage – I need to think about that. One option is to add screw connectors etc. I will not order this board before I have a PSU design + some add-on boards, so we can let the ideas mature a bit.


I used a little trick on the 3-port Galvanic RSX as I connect to ground through the ground layer on layer 0. If you look at the area marked in green this is part of the ground, but the EDA don’t warn me that this is an iceland isolated from actual ground. I added a connection (in yellow circle) to fix the issue.

Just a reminder that an EDA is only a tool. It might contain snags so it’s up to yourself to actually check what it is doing.

RPI Hat / 3-Port RS485 with Galvanic Isolation

I made a 5 port (3 port RS485 and 2 port CAN) earlier that is great, but I want a version that is galvanic isolated for solutions that require wiring around a house or more hash environments. ADM2582E is a “All-In-One” package for this, so using 3 of these I get a 3-port RS485 will full isolation. This will cost ca 15.- USD more than the plain one due to the more expensive isolation chips, but those bucks are worth it.

The 3D model above is a bit premature, but it gives you an idea of how the Hat will look like. I have also included a snip of the PCB to illustrate the galvanic isolation.

I have not connected the 3 ports to the MCU yet as I basically wanted to see if I could achieve 3 ports with proper spacing. I am actually quite happy with the result. The 4 red areas are ground. As we have isolation it means that each port have it’s own isolated ground completely separate.

PLC-/Home Automation -Control System

This diagram illustrate my Home Automation Centre. The idea is to use isolated RS485 networks – no power – to control actuators and sensors. Power will be entered by through RS-X adapters I will draft later. I am a bit undecided on Ethernet/Wifi as this also can be sorted through Raspberry PI. The one thing I do not like with the PI is the SD (TF) card as this is its weakest point regarding reliability. GSM is available low cost and needed for dial-up solutions. The Serial Flash act as a disk. This is only an early idea draft, so lets see where we land.