Designing a M-Bus master for reading heatmeter

[Jagermeister]

I'll design a brand new MBus master for reading one Mbus slave heatmeter device. I thought that i can design it in a USB Stick way. But im struggling to choose the components. Do you have any suggestions for me? Thank you for your time.

 

[FvM]

A M-Bus master interface circit (EN 1434-3 "Full size level converter") has been shown in a recent thread. https://www.edaboard.com/threads/how-does-this-m-bus-master-circuit-operate.407759/

For one unit load and reduced cable length, effort can be reduced. You need at least 25 V bus supply voltage and about 20 mA current capability. If supplied from USB, you start with designing the boost converter.

 

[Jagermeister]

I want to design a master to read individual heaters. The master module will supply itself from the PC. Since the PC output is 5V, I know I have to boost the voltage, but why 25V? Isn't it communicating with 36V/24V levels? Also, what would your suggestions be about the design in general? Thank you for your response.

 

[Jagermeister]

Also i saw this product as a set. Slave(front) and master(behind). Why we need an another slave? Other slaves such as heatmeters doesn't enough to read the data? The master module in the back also comes with a usb port for connecting with PC. So what's the reason that we use another slave?

Sorry for my lack of knowledge but i am a newbie to hardware design and also the communication.

It can be seen that two seperate inputs are there for the PC. I couldn't understand why. Any help or suggestions will be appreciated. Thank you for your time.

 

[FvM]

I know I have to boost the voltage, but why 25V? Isn't it communicating with 36V/24V levels?

About 25 V is minimal voltage for short range (no relevant cable voltage drop), review EN 1434-3 and EN 13575-2. Higher voltage is possible, of course.I remember to have designed 30V supply for M-Bus master.

I'm slightly confused about your examples. You are stating single device in post #1 but are now discussing multi device configuration. Regarding combo of USB stick and black box in post #4, I have no idea what it exactly is. You may want to post a link or full product name.

Usually a master interface is connecting to host computer through a standard serial interface (RS-232, RS-485). But we don't know what the two pin interface on USB stick is.

I presume it's possible to implement a complete master interface for 1 or 2 unit loads as USB stick, including power supply.

--- Updated Jul 20, 2024 ---

Sorry, I didn't read post #1 thoroughly.
You clearly stated that shown stick is a slave device. I think it's intended as a monitor to debug M-Bus communication. You probably don't need it.

The two M+/M- pairs are most likely simply parallel connected.

 

[Jagermeister]

Thanks for your attention. As for as i understand you've designed a mbus master before. Can you share the project with me to take referance from? Also i don't know how to convert from mbus to usb and i couldn't find a good referance, there are different master schematics but they are not the same. I'll review the standarts that you mentioned. I didn't design a project from scratch so im looking a example for taking a referance. I'll design a boost converter for now but rest of it still blank for me.

--- Updated Jul 22, 2024 ---

Quick update:

I found this circuit. From this article:

A Meter-Bus Master Station Interface Circuit Based on Transistor Amplification Characteristics​

Yang Cheng-ying1 and Chen Yong2

https://iopscience.iop.org/article/10.1088/1742-6596/1237/5/052035

I want to supply of the circuit from the USB. What should i change in the circuit? Should i connect the RXD,TXD and GND nets and give 5 V from VDD directly from USB? And then boost the 5V to 36V mark voltage?

And i have some questions too if you have the time to answer:
Are they different things main station interface and converter? I couldn't reach the authors of the respected article.

 

[KlausST]

Also i don't know how to convert from mbus to usb and i couldn't find a good referance,

Did you read M-Bus basics, like the documentation?
M-Bus is a combination of power supply and UART communication with voltage and current.

So all you need is a USB-to-UART converter (besides the M-Bus phy). There are many, from bare ICs to ready to buy modules.

Klaus

 

[Jagermeister]

Did you read M-Bus basics, like the documentation?
M-Bus is a combination of power supply and UART communication with voltage and current.

So all you need is a USB-to-UART converter (besides the M-Bus phy).

Yes i read the documentation but in physcial layer part i couldn't find the requirements for master devices. Also i couldn't read the necessary standards which stated in #5 by @FvM. And i am aware that my level of knowledge is limited on this area, as i mentioned im a newbie.

So as far as i understand, i've to design a uart to usb converter addition to #6's circuit. Also i want to add TX RX and USB status LED's for design. And im unsure about where should i put down the LED's in the design. I am still working on the article to find out where should I place the status LEDs.

There are many, from bare ICs to ready to buy modules.

Do i need to use an IC for the master module? The circuit on #6 doesn't have any.

 

[KlausST]

Do i need to use an IC for the master module? The circuit on #6 doesn't have any.

Circuit on post#6 does not have USB!!!

Klaus

 

[Jagermeister]

Circuit on post#6 does not have USB!!!

Klaus

Oh, i get it. The UART to USB has the IC. Thanks.
I'll start to schematic and update this post soon.

 

[Jagermeister]

Update:

This is the circuit which i made by copying the referance design for the main station ( Not including USB interface yet ). And there are some questions on the circuit as you can see that i couldn't solve by myself. I'm working on them and want to improve it. Also the design is obviously a general circuit so i'll try to make much suitable circuit by changing the values of the components or using different components.

So, what's your suggestions and comments about this circuit? What should i change? Also i randomly select the R9 and D2. Also Q1 and Q3 are general pnp's so i've to choose them for their spesifications and voltages. Any comment will appreciated. Thank you for your time.

 

[FvM]

1k PTC makes no sense, that's a sensor rather than a fuse. PTC fuse is intended as short circuit protection. If your 36 V power supply is current limited, you don't need a PTC fuse. Similarly, TVS protection is only required if your MBUS transmitter is driving a long cable that's expected to pick up surge voltages.

 

[Jagermeister]

So, further in the research i realised that the circuit in the #11 is not the general design. So back to the original schematic at below, i want to learn how to get the required 34V from USB. I know that i've to use boost converter but in the circuit there is a external power supply. How can i cancel the external and supply the m-bus bus from USB? Thank you for your interest.

 

[Jagermeister]

So, further in the research i realised that the circuit in the #11 is not the general design. So back to the original schematic at below, i want to learn how to get the required 34V from USB. I know that i've to use boost converter but in the circuit there is a external power supply. How can i cancel the external and supply the m-bus bus from USB? Thank you for your interest.
View attachment 192662

Update: Deep further the research i rast upon the circuit which made by Jens Mueller. He also wrote a design guide to help the community. I decided to change my referance design to this.

This circuit has RS232 interface already so i'll change it to USB with an IC. He also recommended two different voltage regulators for 5V to 34V.

I will share the updates.
You can find the circuit and guide by Jens Mualler here: https://gitlab.com/jm_wtal/mbus-usb-converter/-/tree/master?ref_type=heads

Also on his personal website: https://pc-projekte.lima-city.de/MBus-Konverter.html

 

[FvM]

I believe both versions will do. The bus interface is almost identical. Don't know if you e.g. need isolation?

 

[Jagermeister]

Update; i did some more research and put in some work on altium to create and finish this design, please check it out and comment your suggestions for further upgrades or changes.

Here is the master design. I intentionally didn't add the UART to USB bridge yet so that i can finish on the analogs.

And this is my regulator choosing and design - which im not proud or sure about - :

Also i noted some issues and problems to ask the forum. So it would be so nice to check it out and suggest me some solutions;

I am working with Celestial Altium Library. Some parts is in there and some not. I'm trying to choose the parts which is in the library for their 2D and 3D models.

Thank you in advance to your suggestions. I'll be waiting for your feedback!

 

[KlausST]

Hi,

the regulator design makes no sense at all.

Neither the input side nor the output side circuit makes sense.

--> Better review the datasheet and it´s circuit examples.


Klaus

 

[Jagermeister]

Hi,

the regulator design makes no sense at all.

Neither the input side nor the output side circuit makes sense.

--> Better review the datasheet and it´s circuit examples.


Klaus

This is the Jens Mualler's design that I am referring. He recommends some step-up regulators that i couldn't understand how they work. Because the circuit works on 34V bus but the recommended regulators just boosting 5V to 15V. Why the input/output sides don't make sense? What should i change? Isn't the referance design correct?

 

[KlausST]

He recommends some step-up regulators that i couldn't understand how they work.

Did you really read the datasheet?

but the recommended regulators just boosting 5V to 15V

No, they don´t.
They boost 5V to DUAL 15V which is 2x 15V (on nominal load) ... and a bit higher on less laod.

Isn't the referance design correct?

It´s like asking: I don´t understand which way to go. Isn´t the map correct.
(Without telling which map you refer to)

I don´t know which reference you are talking about.

Obviously you don´t talk about the Jens Mualler design, because it is completely different.
It usues ready to buy DCDC converter perts, whereas your design shows an IC with some electronic components around.

Klaus

 

[Jagermeister]

Update: after further readings i come up with this regulator that Jens Mualler recommends and i realized that the dual voltage output when Klaus said at #19.

Main station with changed Q1 and Q2;

UART to USB converter with FT232R. Also tried on the FT232H package but i didn't use EEPROM for this.

And that's the ready to buy converter as Klaus recommended.

What's your suggestions? Thank you for your time.