mirror of
https://github.com/UtilitechAS/amsreader-firmware.git
synced 2026-02-03 07:30:21 +00:00
127 lines
4.9 KiB
Markdown
127 lines
4.9 KiB
Markdown
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# Overview
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This represents an alernative PCB for interfacing the HAN M-bus connector
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on AMS meters.
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The biggest difference between this board and [the original board](../Board_001)
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is that this board supports communication over a physical wire.
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So you can for instance use this board together with an arduino to make
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a robust watt-meter display that will never fail because of connection
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issues (unlike wifi).
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This solution uses the industry standard chip for M-bus communication,
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[TSS721A](http://www.ti.com/lit/ds/symlink/tss721a.pdf) with full
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galvanic isolation to the bus, e.g. connecting a cable from this PCB
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to a mains connected PC for instance will not result in a [ground
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loop](https://en.wikipedia.org/wiki/Ground_loop_%28electricity%29).
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The schematic and drawings are made with
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[KiCad](http://www.kicad-pcb.org/).
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# Scope
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## Software
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Reuse existing [code](../../Code).
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## Hardware
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Only support receiving transmitted serial data from the bus since the
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Kamstrup AMS meters have no physical support for receiving anything.
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The primary use case is to be a shield on an Arduino board (e.g. Uno or
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Leonardo). A standalone ATtiny version would be nice to have as well.
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Support daisy-chaining multiple units on the bus.
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# Status
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This is unfinished work, currently just started.
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# Future
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First phase is only supporting converting M-Bus data to serial I/O.
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Support for ethernet or USB will be implicit via Arduino/shields. Later
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standalone versions with ATTiny will be most useful by including
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ethernet/usb support directly.
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## Step 1
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Create a simple M-Bus master simulator (transmit only) that takes
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serial data and modulates onto the bus. Write arduino code to send a
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test pattern and verify on oscilloscope.
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https://electronics.stackexchange.com/questions/99388/designing-a-m-bus-master-up-to-10-slaves/99390#99390
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https://electronics.stackexchange.com/a/214477/568
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## Step 2
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Connect the TSS721A chip with all required components with a optocoupler
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between it and Arduino (e.g. M-Bus to TTL conversion). Connect with the
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simulator from step 1 and verify that received data equals the data sendt.
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Possibly also test with off-the-shelf M-Bus to TTL conversion hardware
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for comparison.
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## Step 3
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Finish PCB design to be a usable Arduino shield. Integrate the
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AmsToMqttBridge software. Display received data on LCD.
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## Step 4
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Put code onto ATTiny on a standalone board with support for either USB
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or ethernet.
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The MCP2221 is an inexpensive<sup>1</sup> USB to serial chip that people
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[seems](https://www.element14.com/community/groups/open-source-hardware/blog/2016/02/01/implementing-non-ftdi-usb-to-uart-serial-interfaces)
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[very](http://www.eevblog.com/forum/reviews/alternatives-to-ftdi-usb-to-uart-converter/)
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[satisfied](https://hackaday.io/project/18845-usb-serial-uart)
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[with](https://hackaday.com/2016/03/04/dual-uarti2c-breakout-goes-both-ways/).
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It does [not](http://blog.zakkemble.co.uk/mcp2221-hid-library/)
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[achieve](https://hackaday.com/2017/05/31/counterfeit-hardware-may-lead-to-malware-and-failure/#comment-3636318)
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the maximum speeds is theoretically supports, but that is irrelevant for
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this project. This board should then be powered by USB, both in that that
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is the most natural and convinient choice and that if not then apparently
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MCP2221 needs some additional electronics in order to [work properly as
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an USB device](https://electronics.stackexchange.com/a/323551/568).
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For ethernet the
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[ENC28J60](http://www.microchip.com/wwwproducts/Devices.aspx?dDocName=en022889)
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chip seems to be the
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[go](https://www.reddit.com/r/arduino/comments/18pw59/diycheap_ethernet_shields/)
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[to](https://www.open-electronics.org/low-cost-ethernet-shield-with-enc28j60/)
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[solution](http://www.instructables.com/id/A-credit-card-sized-Ethernet-Arduino-compatable-co/)
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[for](https://www.pocketmagic.net/atmega8-and-enc28j60-for-ethernet-support/)
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[inexpensive](http://tuxgraphics.org/electronics/200606/article06061.shtml)<sup>2</sup>
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DYI solutions. It only supports 10Mpbs, but that is more than
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good engough for pushing out MQTT messages. It draws a significant
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amount of current (~120mA or more) and gets gets hot so it might
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need heatsinking, but that is an [inherent problem with all ethernet
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controlles](https://electronics.stackexchange.com/questions/52349/why-is-ethernet-so-power-hungry).
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# Schematic
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# PCB
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None yet.
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-------------------
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<sup>1</sup> Less than 20 NOK at [Elfa
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Distrelec](https://www.elfadistrelec.no/en/interface-ic-uart-usb-so-14-microchip-mcp2221-sl/p/11087556),
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cheaper elsewhere.
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<sup>2</sup> 20-30 NOK for the
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[chip](https://www.elfadistrelec.no/search?q=ENC28J60&filter_Category1=&filter_Category1=&filter_Category1=&filter_Category1=&filter_Category1=),
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from 30-40 NOK for the
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[connector](https://www.elfadistrelec.no/search?q=magjack&filter_Category1=&filter_Category1=&filter_Category1=&filter_Category1=&filter_Category1=&sort=Price:asc&page=1).
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