Pulse meters - part 1

Here is some evolution about the Gas Meter 'Gazpar' for which I developped a generic battery backed-up solution.

Gazpar

As mentionned before, the "official" cable is for sale at a hefty price (for what it is) of ~20€. I would have gone for this cable, had the meter been outdoors or in a humid room, but since it is located in my kitchen, I simply used the trick found on some forums: Female dupont wires. And it works very well indeed.

Dupont Female

Counting

One of the main differences between the electricity and gas smart meters, is that the former will deliver all the information (including current reading) in a continuous way. In case of power cut, upgrade or crash of the microcomputer/microcontroller, nothing is really lost and things will restart as soon as possible.

The gas meter, smart or not, will only give pulses... if nobody is listening, the information is lost and the status of the reading not longer accurate.

Keeping the value

The basic idea is to decouple the counting process from the processing unit. The counting unit should not need any update or needs to restart often.

One idea was to write the current value on a flash memory but these are notoriously bad as time goes by. Wear and tear could soon be an issue.

Apprently, there is a kind of memory called Ferroelectric RAM/FRAM for which the number of write cycle is not a problem. But these are not wildly sold (but can be found as breakout board) and certainly overkill for just keeping a counter.

So in the end, the easiest solution seemed to use a basic ATTiny85 powered and keeping the value in RAM. This solution will be described in the next post.

    Gazpar's socket

    As mentioned 9 months ago, the new French smart gas meter is called Gazpar and has a socket. So far I couldn't find any info about it but slowly, details are starting to emerge:

    In this thread (in French), there is a link to a adaptation cable reference EER31130 sold by Schneider Electric for their own product but it looks like it could by used for any solution.

    It also gives an indication of the type of socket (made by JAE but unfortunately I can't find the exact reference).

    JAE connector

    Schneider Electric's "pulse emitter" has the following characteristics which give other info about what the Gazpar might be (open collector (most likely) or reed switch):

    • Compatibility with meters with pulse output of types: Open collector (electronic) / dry contact (mechanical contact), REED switch (magnetic) with the following characteristics:
    • Voltage on the contact: 2.7 V (delivered by the Pulse Emitter)
    • Closed contact impedance: <1 kΩ
    • Open contact impedance: > 1 MΩ
    • Pulse duration: > 66ms
    • Delay between pulses: > 33ms

    A suivre...

    Teleinfo with Wifi on the Linky

    Following the upgrade of my electricity meter (from rotating disk to latest generation of smart meter), I am now able to use the Teleinformation output (hurrah!)

    Linky

    The Linky smart meter has a slot for a "LRT" module and a 3-pin header for teleinfo (the traditionals "I1" & "I2" as well as a power source named "A").

    There are also two communication modes available: Historical (the only one available so far) & Standard (i.e. the new one starting with Linky).

    LRT

    The "Linky Radio Transmitter" (Emetteur Radio Linky) is a module developed to transmit the value to a household display. Specifications show they can be using either Zigbee or KNX. It was supposed to be totally open but I am yet to see a schematics of it.

    ERL/LRT

    At least the Interface Specification is available. I reused the name of Zigbee attributes for the MQTT publication.

    Teleinfo

    Official docs are available (in french) on Enedis's website, in particular NOI-CPT_02E for Teleinfo in general and NOI-CPT_54E for Linky in particular.

    The electronics part is mainly based on work done a long time ago by others, specially Charles Hallard (Démystifier le décodage Téléinformation et l’optocoupleur SFH620 and PiTInfo V1.2, en finir avec la téléinfo capricieuse).

    Board

    My board is vague cousin of Charles Hallard's Wifinfo but where most of the components are already embedded on the nodemcu module.

    CH340G (USB to UART)

    Something worth noting is that CH340G seems to be struggling with 7N1 (7 bits instead of the usual 8). Although it doesn't matter for day to day usage of the ESP8266, it makes tests (emulation of the Teleinfo frames) more difficult.

    It could be the driver though I am using Linux. Using boards (Amica) based on CP2102 or FT232 didn't show any problem.

    Power

    From the meter

    In theory, the pins "A" and "I1" are maint to be used as the power source. That said, the characteristics are 6 Vrms (50 kHz) and 130mW. This is far from the ESP8266 requirements (~ 150mA) and if it would be easy to rectify and smooth the current, a storage system (super cap or battery) would be needed to deliver peaks of currents every time the data is published (re-charging being one while module is in deepsleep).

    External 5V source

    To keep things simple and since I already had a 5V source at my disposal, I used the embeded regulator on the nodemcu board (through the Vcc pin but it could have been through the micro-USB socket).

    OTA

    Having the circuit permanently plugged to the meter means that the option of remote updates is a big bonus. The module is off/asleep most of the time so the best method was the HTTP Server one. But in order to make things easier and more secure, there is a physical jumper to allow OTA or not. When jumper is on open position, no OTA is possible. In the other position (closed), every time the program starts (i.e. every minute), it checks if an upgrade is available.

    This is were the additional python script comes handy. By running a webserver and comparing the MD5 checksum of the firmware on the module to the one on the server, it is possible to launch the upgrade sequence only when necessary.

    MQTT

    Selected data is transferred using the MQTT protocol. As mentioned above, the names/topics used are based of the ones in the ERL/LRT documentation.

    ADCO  --> Serial Number used in topics (ssssssssssss)
    
    BASE  ---->  cm/teleinfo-ssssssssssss/data/index {"value": "000073370"}
    PAPP  ---->  cm/teleinfo-ssssssssssss/data/apparent_power {"value": "00320"}
    IINST ---->  cm/teleinfo-ssssssssssss/data/rms_current {"value": "001"}
    

    Since the tariff is a constant one and not a differential one, there is only one reading to report and there is no need to advertise which tariff is active. People dealing with Heures Pleines / Heures Creuses would have to change the code.

    Deep sleep

    In order to reduce the amount of power drained, reduce the heat production and because there was no need to keep the module on for nothing, I decided to turn the wifi off. But it turned out that it isn't as straightforward as it initially sounded. Just calling the corresponding fonctions doesn't really make any difference in term of power consumption and forums are full of examples looking really like black art.

    On second thought, I decided to go to the deep sleep route which turned out to be easier to implement and perfectly adapted to this kind of usage. The teleinfo is continuous with values coming all the time but having a refresh every second or so has very limited interest. Even everything minute is kind of luxury.

    The only downsides of deep sleep are the need of a physical wiring for reset purpose and that the programme really resets every time. In this case where the bridging is stateless (state/info is held by the smart meter and given every single time) it doesn't matter the least.

    Next version

    This version has been running for a while without any issue. Once the meter is properly registered by the supplier (they seem to have technical issues actually), they should be able to change the mode to "Standard".

    This new mode is only in Linkys, uses a different serial speed (9600N7 instead of 1200N7) and provides more information. The "codes" are slightly different too.

    There is no physical modification needed and everything is documented so making the software changes should not be too complicated.

    Will see....

    Module in its box

    Code

    As usual the code and schematics are available (AS IS) on github.

    CO2/Humidity/Temperature Sensor

    This project is a mashup of different experimentations. I wanted to try the SHT21 sensors and I was looking for a CO2 sensor at the same time accurate and not too expensive.

    Working screen

    CO2 Sensor

    Until recently, gaz sensors were either analogue (and totally uncalibrated) or relatively expensive (when not both at the same time). Then came the MH-Z14 which is a affordable "Non-Dispersive InfraRed" sensor, in theory quite selective.

    The MH-Z19 from the same company can be found for ~ $25. The main issue is the partial documentation. Some commands are still a bit obscure.

    MH-Z19

    A great source of information is the wiki https://revspace.nl/MHZ19 and there a quite a few examples on github to get started.

    At first experimentations were a bit frustrating but after a while things started to stabilise a bit and sensor's readings from the past few month seem to make sense. The solution was to reject sub-standard readings and to average valid ones over a period of 5 minutes.

    One quite annoying thing a bit this module when using breadboard or prototype PCB is that it has weird dimensions (not a multiple of 2.54mm) and won't fit nicely.

    Calibration

    Calibration can also be an issue, specially because of the ABC calibration every 24h. The system would be great if it spanned over let's say a week which would give you several chances to open the window but as it is (i.e. using the minimum value of previous day as base), reading were becoming strange day after day. It turns out that it works a lot better without ABC and a manual calibration from time to time.

    Then manual calibration can be triggered by software or using the hardware pin. To avoid trying to fit a switch on the enclosure, the solution retained was to use a reed switch inside and to press a neodymium magnet on the cover once the air of the room has been well recycled.

    Graphs

    Wemos D1 mini

    Although I initially planned to use nodemcu modules, I decided to try Wemos D1 mini which are smaller, cheaper and able to cope with higher speed communication via USB so firmware upload is twice as fast.

    Besides this, there really behave like any other ESP8266 solution. Wemos offers a good selection of shields (power, relay, LED, sensor, ...) which I haven't tried as well as modules based on the more powerful ESP32.

    It is probably best to use their official online shop as there seems to be quite a lot of fake modules around, and not necessarily cheaper.

    I2C Oled

    Having used a 0.96" Oled screen for the time bomb, I really thought that using a 0.91" 128x32 I2C SSD1306 screen would be trivial. As it turns out, library for the former is not compatible with the latter because they lack of a proper framebuffer. After digging around, I found that the Adafruit library was working (one parameter is of a different value) even if the hardware looks quite different (more pins).

    OLED I2C 0.91"

    To be perfectly honest, if I was to make another sensor, I would give up the screen and use coloured Led shinning through (the plastic is slightly translucent) as the physical fitting was probably the most challenging part of this project (even if simple by DIY standard).

    A sprinkle of MQTT

    Communication with base is, of course, via MQTT, nothing new or complicated here. There is a sampling every minute for the CO2. The average value as well as the current values of temperature and relative humidity are sent every 5 minutes.

    Wifi off (really?)

    Since this new sensor is installed in our bedroom, I wanted to switch the Wifi on only when needed MQTT communication to send the values. I basically used the dedicated function for this. Is is really switching off "radiations"? Who knows... as I discovered with the electricity meter project, electric consumption is not lowered by it.

    Powering the sensor

    I knew from the start that using battery would be a challenge and I didn't even bother. Between the screen, MH-Z19 and the Wifi, it is probably around 200mA anyway. The USB port of the Wemos D1 mini is plugged directly on a small power adapter. The usb cable can also be used to upgrade the firmware as no OTA was implemented on this project.

    All in a "sensor box"

    Like almost everything else, directly from China, I found an enclosure designed for sensors (or thermostat?) which was the right size to fit everything. The USB power adapter is external, the ESP8266 at the top and the thermometer at the bottom, by the vents in order to stay as accurate as possible. Despite this, the temperature appears 1.5°C higher than without cover. The offset can be corrected in software.

    Work in progress

    Starting screen

    Code

    As usual the code and schematics are available (AS IS) on github. It includes a SHT library and MH-Z19 library.

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