ATTENTION

If you have a solar module installed (FM244), the slot for the KM271 is occupied and you can not install the module. We (the KM271 community) found out, that the FM244 has assembly options for the RS232 port but it seems that it is not populated. It should be possible to populate the coding resistor (10K) and break out the RX and TX signals to to be used by the KM271 WiFi. But I suggest to supply the KM271 WiFi by USB then, because the power supply of the Buderus controller is weak and the FM244 is definitely worsening this fact. Stay tuned for further information about this, best by joining the KM271 matrix channel

Updates

2024-08-25

Stock is now very low (3 units left) and I currently do not plan to order a new batch. I currently receive only 1-2 orders a week (declining) and it only makes sense to order 100+ units, otherwise the upfront-cost is too high for an attractive selling price.

Important Notice

• If you are searching for the bare PCB, I created a seperate product page for that
• Please be aware, that the firmware is currently still under development...
• Please also read my blog post on this product (see Dokumentation link below)

What is it?

It is a slot card for some Buderus Logamatic (e.g. 2107-type) that connects the serial interface and attaches it to the serial interface of an ESP32-WROOM-32D/U module to be linked into a WiFi network. You can also write your own firmware to make it Bluetooth connected.

Why did you make it?

Because I need to attach my heating system to my Smart Home since the burner raises an error quite often. I'm then forced to commit the error, wait half an hour for the water to heat up or take a shower with cold water.

Now I can connect it to my Home Assistant using ESPhome and send me some pushover message, as soon as the error occurs.

What makes it special?

The original Buderus KM271 module (with a RS232 level shifter) is not produced anymore and costs around $100. And it still needs some additional hardware to lift it to your WiFi network.

Recently I found out, that Buderus is also selling the KM200 (in version 2) for "as low as" 270 bucks. I did not see it in action yet, but I believe it locks you in to the Buderus cloud and you have no chance to get the data into your smart home...

What does the package (not) contain?

If you order the option with ESPhome, you just need to

• plug it into your logamatic (switch it off for mounting)
• wait a minute for the fallback WiFi to show up
• do what you want (e.g. OTA-upload another firmware)

Alternative firmware based on PlatformIO/Arduino from Sven. Read the docs to see, what great things you can do with it. It also provides a full blown WebUI for all people that don't have a smart home system...

Jens and Bascht added many sensors to the latest ESPhome variant. Most of the commands are already implemented. Mostly the scheduling is not supported, but this is not really needed, if your smart home takes over full control :-)

You do not need the EEPROM if you do not write your own firmware for this module (at least for the moment there is no support planned)

The exhaust sensor circuit allows to connect a 100K NTC Type temeorature sensor for exhaust measurements. You can order a sensor from different sources, like https://www.sensorshop24.de/kabelfuehler-durchmesser-6mm. Select NTC 100K, PFA wire insulation and water resistant. This should serve the purpose very well. The diode in the schematics should be not soldered, if you want to measure temperatures below 80°C (like for a cold exhaust pipe).

Options

I ordered assembled boards that all contain:

• ESP32-WROOM-32D-N8 (8 MB Flash)
• NO Exhaust Sensor circuit & terminal (optional, see above description)
• NO Sensor Header (optional)
• NOT beveled edge connector (should fit without beveling)
• NO EEPROM

I'll solder all your selected options to the board.

For tinkering in depth, I recently wrote some hardware description.

Thanks

The 0.0.1 prototype PCBs have been sponsored by PCBway. I totally can recommend this manufacturer for your own PCBs. A reader of my blog sponsored also 10 PCBs of the 0.0.5 version and added the exhaust temperature circuit.