idea: use 433MHz or 866MHz band to remotely read the power meter
Transceiver: RFM69
attach a sender to the power meter
Power Meter read-out via IR: https://wiki.volkszaehler.org/hardware/controllers/ir-schreib-lesekopf-ttl-ausgang
Sender:
Receiver:
The reciver logs all incoming packages and makes them available for queries via network over ethernet.
Shops:
- https://www.distrelec.de (adafruit)
- https://www.makershop.de (adafruit)
- https://www.berrybase.de
Protocol information:
- OBIS codes https://www.promotic.eu/en/pmdoc/Subsystems/Comm/PmDrivers/IEC62056_OBIS.htm
- SML structure example http://www.stefan-weigert.de/php_loader/sml.php
Power Meter Adafruit Feather 32u4 866MHz Arduino Uno Banana-Pi
ISKRA MT631 --> IR Read Head --------> Ethernet --> InfluxDB
RFM69 RFM69 Grafana
SD-Card
The sender wakes up from deep sleep every hour, awaits an SML (Smart Message Language) telegram from the power meter (which sends one every second through the infrared interface) and stores timestamp and power reading in RAM, returns to sleep. When no more entries can be held in RAM it powers up the RFM69 radio and sends all stored readings.
According to the datasheet the adafruit feather consumes 300uA in deep sleep so that in theory a 500mAh battery is sufficient for 500mAh/300uA = 1666.7h = 69.4 days of operation. With the high power phase every hour it will hopefully still last over a month per charge.
We are interested in two fields from an SML telegram (see the full dump in raw-data/serial-dump-annotate.hex in this repository)
(1) Timestamp (i.e. uptime)
[..]
63 7 1 # getListResponse
77 # List, 7 entries
1 # clientId, no value
B XX XX XX XX XX XX XX XX XX XX # serverId
7 1 0 62 A FF FF # OBIS manufacturer
72 # List, 2 entries
62 1 # choice: secIndex
65 0 11 9C 33 # secIndex (uptime)
[..]
63 7 1 # getListResponse
77 #
1 #
B XX XX XX XX XX XX XX XX XX XX # serverId
7 1 0 62 A FF FF # OBIS manufacturer
72
62 1
65 0 11 9C 34 # uptime
The uptime is 0x00119C33 = 1154099 sec = 13d8h and 0x00119C34 = 1154100 sec respectively. As sanity check: the telegram was received on 2021/04/01 at around 19:00 and the power meter was installed on 2021/03/19 at around 11:00. That matches 13 days and 8 hours.
(2) Power Reading
77 # List, 7 entries
7 1 0 1 8 0 FF # OBIS 1.8.0*255
65 0 10 1 4 # status ?
1 # valTime
62 1E # unit: 1e = "Wh"
52 3 # scaler, 3 = k
62 2E # value: 0x2e = 46 kWh
1 # valueSignature
Field lengths can vary. The current 62 2E = 46kWh will become longer and the 2nd nibble indicates the field length, for example a future reading could be 64 1 2 3 = 291kwH.
To simplify the code on the sender it will not implement a full SML parser that takes varying field length into account. It will be rather dumb: it checks for the occurence of the interesting OBIS code in the byte stream and then store sufficiently many bytes after that to capture the values. The extraction of the values from that SML snippet is done in postprocessing on the receiver.
The timestamp is identified by the byte sequence
7 1 0 62 A FF FF
and the following 12 bytes are stored although 8 byte are sufficient at the moment but we want to allow a growing time stamp field.
Example
63 7 1
77
1
B XX XX XX XX XX XX XX XX XX XX
7 1 0 62 A FF FF <== Marker
72 <== start to store
62 1
65 0 11 9C 34 <== 8th byte
74
77
7 1 0 60 32 1 1 # OBIS
1
1
1
1
4 49 53 4B # 49 53 48 = "ISK"
1
The power reading is identified by the byte sequence
7 1 0 1 8 0 FF
and the following 20 bytes are stored although 12 bytes are sufficient at the moment but we want to allow a growing power field.
Example:
77
7 1 0 1 8 0 FF <== Marker
65 0 10 1 4 <== start to store
1
62 1E
52 3
62 2E <== 12th byte
1
77
7 1 0 2 8 0 FF # OBIS 2.8.0*255
1
1
62 1E # "Wh"
52 3 # "k"
62 0
1
The following information is stored each hour:
- timestamp: 12 bytes
- power reading: 20 bytes
- battery level of the sender: 2 bytes (int)
A total of 34 bytes - after 24h this amounts to 816 bytes which fits into the 2KB memory.
The receiver is an Arduino with RFM69, Ethernet and SD-Card. It loops over events from Ethernet and the radio. When it receives new data via radio from the sender, which should be 816 bytes every 24h, it appends it to data on the SD-Card. The content of the SD-Card can be accessed through the udp protocol over the ethernet shield.
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