Port expanding HAT for the Raspberry Pi
1 Dec 2016
2 minute read


By development of a new version of our heating control, I was dealing with several ideas like designing a new microcontroller pcb, using an ESPXY-device or the most luxurious solution using a Raspberry Pi board. All three solutions open three different grades of performance, effort and possibilities for further ideas. In the past I spend several months of playing with self designed AVR microcontroller boards. These boards are communicating and interacting through a self-constructed ISM1 network and I’m proudly able to say: “Since I have installed them, they had worked all the time.”

The hardware is very simple: A self-designed power supply, an Arduino Duemilanove with a simple shield (soldered by hand and under usage of parts laying around) and a relay card For the frontend I’m using FHEM2 and a couple of modified and handwritten modules.

The reasons why

The days become shorter and colder too. The Arduino based solution works very well in the meaning of “if we don’t put the lid on the enclosure”. There is no problem with the control itself, but the enclosure is damping the rf-signal. So in some cases I mentioned signal and packet loss. By the way the electrical installation isn’t that good, so there would be plenty tasks. Any possibility of changing the existing setup would cause the same effort in time and money like spent some time in creating a new more reliable solution with room for some additional but currently unnecessary improvements.


In the last week I was dealing with the idea of buying an UniPi-board. Unfortunately I’m very restricted in space, so the UniPi would not fit and I decided to spent a some spare time (collected hours of overtime) for designing the new control.

The redesign is based on an Raspberry Pi 3 and a B+ HAT3. The HAT itself was the main task, because of the high integrated embedded PC comes with lot of nicht features. Like onboard ethernet and wireless LAN4 controller and needs only to be extended with some kind of electronics.

In my case this means that I have to design some kind of GPIO5 extension, like a port expanding device.

Board on E-CAD software

The PCB was ordered on December the 1st and currently is on sipping to me. So it’s time to collect the needed parts.

Bord preview on OSH

  1. Industrial, Scientific and Medical [return]
  2. Freundliche Hausautomatisierung und Energie-Messung [return]
  3. Hardware attached on top [return]
  4. Local area network [return]
  5. General purpose input and output [return]

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