STM32L0LoraTx

Firmware and PCB for a device that sends data with a STM32L0/RFM95, battery or solar powered, to a LoraGW ESP8266/RFM95 node

Build

Download and install STM32CubeIDE (as of now version 1.5.1)
Import this repo
Open .ioc file and select "Project/Generate Code" (should download needed "firmware" files for the chip from ST)
Build Release or Debug

Wiring

connect Gnd of all components

STM32L011

Not checked without, but generally recommended to use a small ceramic (~10nF) and big electrolyt condensator (~10µF) between + and - near STM pins

Look at the ioc file with CubeMX pinout view.
Vdd and Vdda to 1.8-3.3V
Vss to Gnd
Boot0 pulled to Gnd (~10k) to safely boot from flash
STLink for flashing and debug: SWD, SWC, Gnd, NRst (also can provide Vdd via JP1 and STLink-Rx to L0-Tx for serial out)

BME280

SDA=MOSI, SDC=MISO, others should be obvious

RFM95W

Ant=~8cm wire (vary length and position to get best average RSSI as reported by LoraRx).
NSS=CS, others should be obvious

Serial

Rx of a usb to serial converter sends at 115200. I use this command (serial port name ttyUSB_ser_red is defined in my /etc/udev/rules.d) pio device monitor -p /dev/ttyUSB_ser_red -b 115200

LED

can be used without resistor. I use 1kOhm to save battery

References

Good resource for STM32 is Stefan Frings He has links to reference, datasheet, errata and more. E.g.:

Power Info Bits

Examples for LL are here: STM32Cube/Repository/STM32Cube_FW_L0_V1.11.2/Projects/NUCLEO-L073RZ/Examples_LL/RTC/RTC_ExitStandbyWithWakeUpTimer
Periodic wakeup timer is in Reference 22.4.6 (Periodic auto-wakeup)
1s to 18h periodic wakeup with ck_spre = 1s (see 22.4.3) and WUCKSEL [2:1] = 10
Enable by WUTE bit in RTC_CR register
Once setup it runs in normal and low power.
Sets WUTF flag in RTC_ISR if elapsed and reloads RTC_WUTR (timer counter). User resets WUTF
Set WUTIE bit in RTC_CR to generate interrupt to wake up from low power modes
System reset and Sleep, Stop, Standby have no influence on the WUT (wakeup timer)
Save Lora frame counter in backup register: Reference 22.7.20 RTC backup registers (RTC_BKPxR)

I couldnt make it work with LL lib, had to use big fat HAL for RCC and RTC. What is missing?

  LL_RTC_DisableWriteProtection(RTC);
  LL_RTC_WAKEUP_Disable(RTC);
  while( !LL_RTC_IsActiveFlag_WUTW(RTC) );
  LL_RTC_WAKEUP_SetClock(RTC, LL_RTC_WAKEUPCLOCK_CKSPRE);
  LL_RTC_WAKEUP_SetAutoReload(RTC, 3); // wake up every 3+1 s
  LL_RTC_EnableIT_WUT(RTC);
  LL_RTC_WAKEUP_Enable(RTC);
  LL_RTC_EnableWriteProtection(RTC);
  while( LL_RTC_IsActiveFlag_WUTW(RTC) );
  LL_RTC_ClearFlag_WUT(RTC);
  NVIC_ClearPendingIRQ(RTC_IRQn);

Status

Working and sending LoRa packets to my LoraGW ESP8266 gateway (battery voltages and bme280 weather data)

Two devices operating with 2 AA 1.5V batteries (so far using 0.2-0.4 V per year, so >5 years between battery swaps is more than realistic). They send battery voltage data from within a car trunc - not ideal for RF :) - to a nearby house with no signal problems.

One device runs "forever" with a 3.7 Lipo ~1.6Ah, a ~3x8 cm² 5V solar cell and a small solar charger board (reducing vcc out a bit with a diode). No capacity problems during winter.

Todo

Provide more sensor data (probably more ADC stuff and more generic)
Move GPIO pins (CS, LED) to non-ADC pins to have them available for voltage measurements

joba-1/STM32L0LoraTx