Weather station part 1: Pressure and temperature

Introduction

I’ve decided to try to put together a solar powered wireless weather station this summer. It will consist of two parts: an outstation comprising of a pressure/temperature sensor attached to an STM32F030 MCU; all powered by a cheap solar panel and a rechargeable battery. The MCU will use an NRF905 radio module to send data back to a base station within the house which will display it on screen. Power consumption in the outstation will have to be kept to a minimum.
The base station will consist of an STM32L011 Nucleo board and an NRF905 module. It will interface to the host PC using the built-in UART.

The pressure/temperature sensor

About a year ago I bought a BMP180+HMC5983 module from dx.com. The BMP180 component is a very sensitive atmospheric pressure and temperature sensor with an I2C interface. The HMC5983 is a digital magnetometer may have a future role to play in the weather station.

The outstation MCU

I have previously posted a description of how to mount the STM32F030 TSSOP-20 MCU on a breadboard friendly breakout board. These MCU’s can be configured to consume very little energy. I had several of these lying around so the seemed the logical choice.

Wiring

stm32f030_bmp180
The image above shows the wiring involved. The bmp180 module has built-in pull-up resistors so its quite simple. The code on the other hand is quite complicated. The BMP180 has a very strange conversion routine that takes the sensor outputs and converts them to pressure (in Pascals) and temperature (in degrees C x 10). The measurement results are output via the UART TX pin on PA9. I connected this to the host PC using a USB/Serial converter.
The code can be found here. It includes a lot of debugging code that was useful during development. This is very much version 0.1 as it does not take power consumption into account in any way. That will be the subject of a future post.

A very low cost STM32F030 dev board

Aliexpress have begun shipping a low cost breakout/development board for the STM32F030. The board can be programmed using ISP and a USB/UART interface as shown below. The boards cost varies but I got mine for 1.58 Euro.
stm32f030board
I had previously worked on some suitable examples which can be found over here.
These examples are built using a Makefile however I have found that the following script is a lot easier to work with (just make sure your PATH environment variable includes the directory where the arm compiler programs and utilities are stored).

arm-none-eabi-gcc -static -mthumb -g -mcpu=cortex-m0 *.c -T linker_script.ld -o main.elf -nostartfiles 
arm-none-eabi-objcopy -g -O binary main.elf main.bin
arm-none-eabi-objcopy -g -O ihex main.elf main.hex

You then program the chip by linking the Boot0 pin and 3v3 with the jumper, hit reset and enter the following:

stm32flash -w main.hex /dev/ttyUSB0

To run your program, move the jumper so that it links Boot0 to GND and hit reset.
The USB/UART interface appeared as /dev/ttyUSB0 on my system, yours may vary (on Windows it will be something like COM3)
stm32flash can be downloaded from a number of sources. On Ubuntu it can be installed with

sudo apt-get install stm32flash

The ARM cross compiler suite can be downloaded from launchpad.net

Aliexpress link to the board.

The Nucleo ST-Link reflashed as a J-Link debugger

ST Microelectronics recently announced that the ST-Link debug interfaces on their boards can be reprogrammed as Segger/J-Link interfaces.  Curious, I flashed the firmware on to such a debugger as directed here https://www.segger.com/jlink-st-link.html .

I then wired the debugger to an stm32f030 as shown in the pictures below (the debugger had been snapped off the Nucleo board because the target MCU had been damaged)
JLink_stm32f030_2

JLink_stm32f030_1

The SWD connections are taken from CN4 and joined to the corresponding pins on the STM32F030.  Note the way the 3.3V is taken from the top of the jumper JP1:  The jumper must remain in place to power the debug interface.

Important: The Boot0 pin must be pulled to ground with a resistor or the CPU will boot to ISP mode and you won’t be able to run your test program.

In addition to the SWD connections, the STM32F030’s UART is connected to the TX and RX pins on the debug interface.  This allows an application running on the STM32F030 to send data to the host PC.

All of this was done in Ubuntu Linux using OpenOCD.  The OpenOCD configuration script (tbrd.cfg) is shown below:

 

# This is for the STM32F030 connected to the ST-Link Nucleo
# programmer that has been reflashed with the J-Link firmware

source [find interface/jlink.cfg]
transport select swd
source [find target/stm32f0x.cfg]
adapter_khz 1000

reset_config srst_nogate

The debug arrangement worked well: programs loaded quickly, registers could be examined and breakpoints set etc.

To run openocd type the following:

sudo openocd -f tbrd.cfg

In a new terminal window, run arm-none-eabi-gdb

The transcript for a simple session is shown below.

GNU gdb (GNU Tools for ARM Embedded Processors) 7.10.1.20160923-cvs
Copyright (C) 2015 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "--host=i686-linux-gnu --target=arm-none-eabi".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word".
(gdb) target remote :3333
Remote debugging using :3333
0x00000000 in ?? ()
(gdb) monitor reset halt
target state: halted
target halted due to debug-request, current mode: Thread 
xPSR: 0xc1000000 pc: 0x080000b4 msp: 0x20001000
(gdb) load main.elf
Loading section .text, size 0x328 lma 0x8000000
Start address 0x8000000, load size 808
Transfer rate: 3 KB/sec, 808 bytes/write.
(gdb) continue 
Continuing.