Overview
This board can be used to simulate a M-Bus master unit instead of connecting to the real AMS unit, i.e. usable for test and development. It takes a 5 V TTL level input (serial) signal and converts it to a M-bus level signal. It only supports sending. Based on MBus_USB.pdf1. It depends on an external power source capable of delivering 25-40 Volt. Most DC-DC boost/step-up converter modules2 should be fine for this.
BOM
- D1 13V zener
- Q1-Q3 NPN transistor
- Q4 PNP transistor
- R1 1k
- R2 6.8k
- R3 1 (optional, can be shorted instead)
- R4 150
- R5 22k
- R6 220k
Note for the zener. This board depends on the zener to operate below 1mA, e.g. like 1N5350 whereas a BZX55 will probably not operate properly.
This could be accomplished by reducing the 22k resistor so that it draws enough current.
1 See also https://electronics.stackexchange.com/questions/99388/designing-a-m-bus-master-up-to-10-slaves/ and https://electronics.stackexchange.com/a/214477/568.
2 Like for instance this one for £3.