# How to interface optical M-bus on heat meter

I have Landys Gyr heat meter 2WR6, which has optical port for M-bus communication. I would like to periodically read its values via Arduino / RPi / NodeMCU / whatever.

From the technical manual (p. 7), it has:

Optical interface   Standard, EN 1434-3
Communication       Optional: M-Bus or pulse output
Protocol            IEC 870, 300 baud in Nb


and this datasheet says:

ULTRAHEAT 2WR6 heat meters are all equipped with an optical interface to IEC 870 as a standard, e.g. for connecting the tool PappaWin for parameter setting and diagnostics. Note: for the optical communication with the 2WR6 a n optohead with echo suppression is necessary

My model does not have any wire output. So I'm not sure if the optical interface is in fact M-Bus or not and if that IEC 870 protocol applies also to the optical interface. All references I have googled about EN 1434-3 are about wire physical layer, not optical. For optical I have googled EN 62056-21.

So the question is how this optical interface works. Will simple IR diode + IR photodetector connected to serial port work as the physical layer or more is needed? Can this be bought ready-made for a reasonable price?

Which protocol does it use? For EN 62056-21 there is openHAB binding, which I could use probably. I guess I must first send some request to the meter and it will then reply with all the data.

The optical port is on the following picture (which is Tx and which Rx?):

• Ask the manufacturer (duh!). – Olin Lathrop Oct 11 '16 at 11:23
• @OlinLathrop manufacturer sells their original SW and HW for readout, but for huge price. I don't think they will provide me information needed for DIY approach (although built on top of industry standards). – Marki555 Oct 11 '16 at 11:49