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Electrical/Board_003/README.md
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# Overview
This board can be used to simulate a M-Bus master unit instead of
This board can be used to simulate a M-Bus master device 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.pdf](https://github.com/rscada/libmbus/blob/master/hardware/MBus_USB.pdf)<sup>1</sup>.
It depends on an external power source capable of delivering 25-40 Volt.
Most DC-DC boost/step-up converter modules<sup>2</sup> should be fine for this.
to a M-bus level signal. It supports both sending and receiving.
Inspired by [MBus_USB.pdf](https://github.com/rscada/libmbus/blob/master/hardware/MBus_USB.pdf)<sup>1</sup>,
although significantly improved by using zener diodes so that it is
flexible and can work with any external power source between
21 and 42 Volt. Most DC-DC boost/step-up converter
modules<sup>2</sup> should be fine for this.
![](MBus_Simulator.png?raw=true)
## 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
* 1 x zener diode [13V](https://www.elfadistrelec.no/en/zener-diode-017aa-13-on-semiconductor-1n5350bg/p/17006687) (note below)
* 1 x zener diode [4.7V](https://www.elfadistrelec.no/en/zener-diode-do-35-500-mw-vishay-bzx55c4v7/p/30030851)
* 1 x [BD136 transistor](https://www.elfadistrelec.no/en/power-transistor-to-126-pnp-45-no-brand-bd136-16/p/17130046) (most pnp bjt will probably work (with 40+ operating voltage))
* 4 x [BC337 transistor](https://www.elfadistrelec.no/en/transistor-to-92-npn-45-800-ma-diotec-bc337-25bk/p/30012857) (probably any npn bjt will do (with 40+ operating voltage)
* 1 x resistor 82 ohm
* 1 x resistor 1k
* 1 x resistor 8.2k (you can use 10k if power supply is well above 21V)
* 5 x resistor 10k
* 1 x resistor 220k
* 4 x pin header 1x2
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.
Note for the 13V zener. This board design depends on the zener to
operate below 1mA, e.g. like 1N5350 (figure 8) whereas a BZX55
(figure 9) will maybe not operate properly.
![](zener_ok.png?raw=true) ![](zener_not_ok.png?raw=true)
This could be accomplished by reducing the 22k resistor so that it
This limitation could be lifted by reducing the 8.2k resistor so that it
draws enough current.
## Schematic
![](MBus_Simulator.schematic.png?raw=true)
[SVG version](MBus_Simulator.schematic.svg?raw=true)
## PCB
![](MBus_Simulator.B.Cu.png?raw=true)
[SVG version](MBus_Simulator.B.Cu.svg?raw=true)
![](MBus_Simulator.F.Cu.png?raw=true)
[SVG version](MBus_Simulator.F.Cu.svg?raw=true)
## Version history
Rev A - Only transmit. Wrong design, does not work.
Rev B - Both transmit and receive. Should work (not tested yet).
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