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Remake Elektor weather station

Status: Opzet
23 oktober 2019
This a remake of the Weather Station published in the January 2019 issue of ElektorLabs. There were some issues with this project -both in hardware and software- that needed to be tackled. Also we got request of adding a few functions to the station that can't be done with the current PCB anymorewithout heavy soldering. That's why we decided to revise the hardware completely, keep the sensors (and add some more sensors) and rewrite the firmware to make improve the functionality of the weather station.

[Update 3.12.2019]

We have the set of feature ready for now. The PCB in the cylindiric part of the plastic ( the barometer one ) will not be used and replaed with our own PCB. For more comfort you can still use the connectors as they will also be there and just move from there to the ESP32. This new PCB also now houses a propper place for the BME280 from the Elektor Shop, so no longer big amounts of hotglue are requiered to place it. Also we plan to add a second sensor connector for a pure pressure and temperature sensor. All connections to the sensors are made with I²C, besides the plastic parts for the windspeed , direction and rain amount. We will keep the signals and connect them directly to the ESP32.

This will result in 7 wires requiered here, VCC ( we used 5V and a LDO to get 3.3V ) , GND, RAIN, WINDSPEED, WINDDIR, SDA and SCL. This means you can use cheap 8 wire cables like those found in ethet ones to connect the station to the ESP32.

For the ESP32 we changed the enclosure. With the last one it was a bit tricky to get the cables waterproof to the inner. We now have a enclosure with predefined breakoutpoints for the cables and a transparent cover, so you can see inside the station. And here come a few changes.

The last station had a kind of charging circutry for solar pannels and lead battery cells. As solarcharger are now not that expensive any more and will do a much better job that the simple components used in the old station, we removed this compleatly. Instead we setup a propper under voltage lockout, so that your batterys won't get deeply discharged over time.
The powerinput will still be 7 to 12 Volt and using a DC / DC converter build up from THT parts. What is added is a little I2C LCD ( 2x16 Character ) as option and also some buttons for navigation. We added a sd-card slot, so you can write the datat to a sd-card for later use or storrage.

Something else? Yes, we reserved a bit of space for a LoRa-Module ( RFM95 ), so you can send Data also using LoRa or even LoRaWan. This means the station can gain a bigger range than with the WiFi alone.

Last but not least you can connect a particle sensor to the station. This can be a SDS011 or a HPMA115S0-XXX. We may add more sensors later, but for now that shall be enough in the beginning. 

Software will be changed to acommondate for the new hardware attached to it, but all dirvers that were inside the old station will be included into the new one. As we have a spare Pin left in the Cable and some spare pins on the ESP32 we can also consider adding a DS18B20 pin to the station.

The main problem of the ESP32 pico board still is power consumption, as these will be at 100mA averrage at 5V input. This is due to the ESP32 and the WiFi and 25mA will be drawn useless from the USB-Serial converter on the board, as the shutdown pins are not connected, nor they can be controlled form the ESP32 without soldering.
To get powerconsumption less worse we will add a start / stop mechanism to the WiFi that it is only activated if the station needs to send data. This will also mean that, if this mode is activated the usual config via WiFi won't work any longer.

So as you can see we have some work to do now, to make the new station ready in time for the spring season. The good thing is that those who already have a station can mostly swap the PCB as we keep the picokit as its main MCU.

[Update 9.12.2019]

The basic bits for the rain and windsesor are done and the PCB is on its way. The next thing will be the WiFi, as we will add the start - stop mode and the datat upload. Also the LMIC has been implimented to allow LoRa communication, but the LMIC and the ESP32 are not really freinds, as the RTOS somtimes causes a bit of a hassle.

[Update 11.12.2019]

So far drivers for the HPM115S0 and SDS011 are implemented and working. For the SDS011, the last one we had in the lab sadly has a mail function, as the fan is not working or we send accually the command for selfdistruct. The HPM115S0 form honnywell is working and an abstraction lays let the software switch for both parts without heavy codechanges. This also means we can support more particle sensors in the future.

For the I²C Bus we have now basic support for:
- BME280 ( 0x77 / 0x76 )
- Wuerth WSEN-PAD ( 0x5C / 0x5D )
- Veml6070 ( 0x38 )
- TSL2561 ( 0x29 / 0x39 / 0x49 )
- VEML6075 (0x10)
- TSL2591 ( 0x29 )

Next thing will be the wifi and the start stop mode. Also on tge todo list is 1-Wire for DS18B20 sensors.

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