Reading a bunch of BLE sensors with raspberryZero

Apparently maintaining an onpen BLE conection uses a lot of precious miliamps.

The modules ran out of battery after 1 month of constant streaming.
Only one sensor is still working, they stopped broadcasting one by one in the spam of one week.


I have in mind two solutions for this:

1. Instead of a permanent BLE connection and constant streaming of data,
   the raspberry could each 2-5 minutes create a BLE conection and read the temp+humidity data once, then close the connection.
2. Modify the firmware/use a modified version of the xiaomi sensors, so they include temperature and humidity data in their advertisment data.

https://microchipdeveloper.com/wireless:ble-link-layer-packet-types

TODO: review and fix the javascript nodered node, it looks like we have a signed/unsigned problem.
I only noticed because this days temperatures dropped below 0ºC

parseInt()<----yes im talking to you  

Edit: i found out javascript is expecting us to add the "-0001" character for negative hex values (instead of translating the int16_t 2's complement "ffff" so we need to parse it ourselves)
https://stackoverflow.com/questions/13468474/javascript-convert-a-hex-signed-integer-to-a-javascript-value

msg.temperatura = parseInt(msg.temperatura, 16);
if ((msg.temperatura & 0x8000) > 0) {
   msg.temperatura = msg.temperatura - 0x10000;
}
msg.temperatura=msg.temperatura/100;

BLE conections are still working after 2 days

Now i can start to see what a day temperature/humidity footprint looks like

Its funny how it looks kind of like the charging and discharging of a battery

Managed to save received data to influxDB and display it with graphana.
So far only two devices are connected, 12h working uninterrupted .TODO: update the uild steps with influxdb and grapana setups

I managed to maintain 9 simultaneous BLE conexions, enable the notifications for the specific characteristic im interested in.

Receive all notifications and decode the bytes in the payload

The gatttool doesnt allow me to connect a 10th BLE device, i feel the bluetooth chip really struggling when opening more than 5 BLE conections, this would not happen with a raspberryPi4 (different more powerfull wirelles chip) or a raspberryPi3 without active wifi conections