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Temp. and Humidity Logger for the RPI4b

This is a simple temperature and humidity logger for a Raspberry Pi 4B running FreeBSD 14. It is capable of taking temperature and humidity every 5 seconds and storing them into a database. The measurements can then be viewed using either the integrated display, or, they can be exported to a USB drive.

Goals

One of the most important goals for this project is that this device should be low maintenance. Therefore, you should not have to connect it to a computer or the network for years at a time. As this device has not yet been in service for more than a few weeks, this cannot yet be guaranteed, however, it has been designed to, at least in theory, be capable of this. It allows you to change the device's time, date, and timezone from the built in display, as well as allowing you to export data and clear the internal storage of collected data. Finally, it should be able to survive a full drive, however, as there are a lot of variables, it may not be able to.

Contents

  1. Construction
  2. OS Preparation
  3. Installation
  4. Configuration
  5. Usage

Construction

The following is a general list of materials required:

  • 1x Raspberry Pi 4 Model B 1
  • 1x Breadboard (medium or large)
  • 4x Push button
  • 1x DHT11/DHT22 2
  • 1x DS3231 (or other RTC)
  • 1x 16x2 HD44780U based LCD (such as a 1602 LCD, not I²C)
  • 1x N-channel MOSFET (optional, for turning off the screen)
  • 1x Schottky diode (optional, for turning off the screen)
  • 1x 1kΩ resistor 3
  • 2x 10kΩ potentiometers (optional, for display brightness and contrast control)

The following is one possible way to assemble the device. It should be noted, however, that all of the pins are configurable. Thus, the following design should be modified depending on the exact make and model of the parts being used.

Breadboard diagram of a circuit.

If an I²C device will be used (such as the DS3231 or an I²C sensor), care must be taken that the data lines are connected to GPIO pins 2 and 3 (physical pins 3 and 5). If they are not, the configuration files provided in this repository will need to be updated to reflect the new I²C bus location. If multiple I²C devices are used, multiple busses will need to be created. For more information about I²C on FreeBSD see the following man pages: iic(4), iicbus(4), and fdt(4).

Some images of a fully assembled and working unit follow:

A finished build

A finished build

OS Preparation

This software was designed and tested on a system running FreeBSD 14.0. However, it should work on systems running FreeBSD 13 as well as on systems running future versions of FreeBSD. The FreeBSD installation process is very well documented in The FreeBSD Handbook. For convinience, the general procedure is also provided below. If any issues arise or you have any questions, be consult the handbook.

First, download the latest image for the Raspberry Pi here. It is also a good idea to pick up the checksum file. Once done you should have two files with names similar to FreeBSD-14.0-RELEASE-arm64-aarch64-RPI.img.xz and CHECKSUM.SHA256-FreeBSD-14.0-RELEASE-arm64-aarch64-RPI. To verify the downloaded files, open a terminal and execute the following commands (use sha512 if you downloaded the sha512 checksum file):

  • GNU/Linux and FreeBSD: 
    sha256sum -c CHECKSUM.SHA256-FreeBSD-14.0-RELEASE-arm64-aarch64-RPI
  • OpenBSD: 
    sha256 -c CHECKSUM.SHA256-FreeBSD-14.0-RELEASE-arm64-aarch64-RPI

For other operating systems, please consult the relevant documentation.

Because device numbering is not persistent across boots, the export feature of this software does not allow a specific device to be excluded from the list. This may in the feature be rectified by an update, but for now, it is recommend to install the OS to a microSD card. Most Raspberry Pis come with a small USB device that can be used to write to microSD cards, as well as the microSD card itself. If not, you can find both online very cheaply. Once you have connected your device find it's device file using a tool like fdisk or geom. Then execute the following commands as root to write the image to the microSD card:

unxz FreeBSD-14.0-RELEASE-arm64-aarch64-RPI.img.xz
cp FreeBSD-14.0-RELEASE-arm64-aarch64-RPI.img /path/to/device
sync

If you are not comfortable with performing this operation on the terminal, another option is to use software such as balenaEtcher.

Once this process is done (which may take a while), insert the microSD card into the Raspberry Pi, attach a keyboard and monitor, and plug the Pi in to turn it on.

Installation

Once the system has booted and you see the login prompt, enter root as the username and leave the password blank. You should now see a shell prompt. The first thing to do is to configure the temperature sensor and the RTC. To do the former, append the following to the end of the /boot/loader.conf file:

# Load the DHT11/DHT22 kernel module
gpioths_load="YES"
# The GPIO bus that manages the pins that the sensor is connected to
hint.gpioths.0.at=gpiobus0
# This number should have only the bit set for the position corresponding to the
# GPIO pin number that the sensor is connected to. For example:
# 2097152 -> 1000000000000000000000 -> pin 21 (bit 22)
# 1 -> 1 -> pin 0 (bit 1)
# 2 -> 10 -> pin 1 (bit 2)
hint.gpioths.0.pins=2097152

# Load the DS3231 kernel module
ds3231_load="YES"
# The I2C bus the controls the pins the sensor is connected to
hint.ds3231.0.at=iicbus0
# The *8 BIT* address of the sensor. The following is the default for a DS3231
# addr = 0xd0
hint.ds3231.0.addr=208

The FreeBSD base system comes with the text editor vi. For information about how to use it, execute man vi or see vi(1).

The next step is to enable I²C for the DS3231. Once again, append the following to the end of the [all] section of the /boot/msdos/config.txt file:

# Set the initial state of pins GPIO 2 and 3. Change this if you use different pins.
gpio=2,3=a0
# Load the overlay for an the DS3231 I2C real-time clock
dtoverlay=i2c-rtc,ds3231

For example, the /boot/msdos/config.txt file on my Raspberry Pi 4B looks like this:

[all]
arm_64bit=1
dtparam=audio=on,i2c_arm=on,spi=on
dtoverlay=mmc
dtoverlay=disable-bt
device_tree_address=0x4000
kernel=u-boot.bin
gpio=2,3=a0
dtoverlay=i2c-rtc,ds3231

[pi4]
hdmi_safe=1
armstub=armstub8-gic.bin
enable_uart=1

If you want, you can also change the root password at this point:

passwd

After doing this, reboot the system. Once done, execute the following commands:

sysctl dev.ds3231.0.temperature dev.gpioths.0.temperature

If you get a warning about an unknown oid, it means that the sensor is not installed or configured correctly. The following commands can help in debugging the problem. For example, if the battery in the DS3231 has gone bad, the above command will show no error, however, the below command will print a warning message.

dmesg | grep -i ds3231 # for ds3231 debugging
dmesg | grep -i gpioths # for temperature sensor debugging

It should be noted that FreeBSD does not currently support wireless on the Raspberry Pi 4 at the time of writing. Thus, you will need to use a wired connection (or consult the handbook for information about other ways to get packages).

Once the sensors are detected and we have internet, we can install the dependencies for this software. Execute the following command to bootstrap the binary package manager pkg(7) and install sqlite3 and curl.

pkg install sqlite3 curl

When prompted to install pkg, type y and then press enter.

We can now download the source of this software:

cd /tmp
curl -O "https://git.zander.im/Zander671/rpi4b-temp-humidity/archive/main.tar.gz"
tar xf main.tar.gz
cd rpi4b-temp-humidity

If you do plan on connecting the device to the internet long term (remember to arrange for it to be updated!!!), you can enable the ntpd and ntpdate services to sync with an NTP server.

service ntpd enable # sync periodically
service ntpdate enable # sync on boot

At this point, take a moment to edit the config.mk file to to change any default options. These can also be changed after installation by editing /usr/local/etc/rpi4b-temp-humidity/config.conf.

Once you have configured everything to your liking, execute the following command to build and install the software.

make install

Configuration

The final step is to configure the software via the /usr/local/etc/rpi4b-temp-humidity/config.conf file. Once you have done this to your liking, execute the following command to enable the software on boot:

# Optional, set an alternate config file path
sysrc rpi4b_temp_humidity_config_file="/path/to/your/config/file"
service rpi4b-temp-humidity enable

The following command line flags are supported:

  • -h: print a simple help message, then exit
  • -v: enable more verbose output
  • -s: exit immediately if an error is found in the config file
  • -f: specify a different config file path

These can also be modified via the following rc.conf(5) variables (or via the sysrc(8) command).

  • rpi4b_temp_humidity_config_file: same as -f
  • rpi4b_temp_humidity_strict_config: same as -s
  • rpi4b_temp_humidity_verbose: same as -v
  • rpi4b_temp_humidity_log_file: file to write output to, set to empty to discard output

Usage

The buttons from closest to the display to farthest are: select, back, up, and down. When the device first turns on, the stats screen will be shown. This screen displays the current temperature, humidity, and time. Pressing the back button will take you to the main menu. The following is a short description of each screen:

  • Current stats - the current time, temperature, and humidity
  • Stats by - show stats by a specific period (e.g. hour, day, week). Press the select button while on a stats screen to cycle what is displayed. Use up and down while on a stats screen to got to the next or previous period.
  • Data points - view individual data points. Press up or down to go to the next or previous data point.
  • Average range - show stats between two times. This has the same controls as the "Stats by" screen above.
  • Export - export data to a plugged in USB drive. Only file-systems detected by fstyp(8) are supported. If a drive with an unsupported file-system, or no file-system, is selected, you will be prompted to format it as FAT32. Exports can be done in both sqlite3 and CSV format. The temperature is in deci-Kelvin (1/10 of a kelvin) and the humidity is an integer percent (ex. 53% would just be 53). The time is seconds since January 1, 1970 UTC.
  • Blank display - turn off the display. Press any button to cancel. You must have specified a "bl_pin" in the config file.
  • Power options - re-initialize the program, shutdown or reboot the device
  • View date/time - show the current date and time down to the second
  • Set date/time - set the current date and time. The time entered is in local time.
  • Set timezone - set the timezone. The prompts will guide you through creating a timezone as described in tzset(3). Another, possibly easier to understand description can be found in the corresponding Linux man page tzset(3).
  • Clear data - DELETE ALL DATA on the device. When the operation is complete, the database will be empty. NO BACKUP IS MADE so be careful.

  1. Other versions and models will very likely work (such as the Pi 3B), the wiring will just need to be adjusted. ↩︎

  2. Any temperature and humidity sensor for which a FreeBSD kernel module exists will work. You can even use separate sensors for each! ↩︎

  3. If your DHT11/DHT22 is mounted on a carrier board with only three terminals, it likely already has this resistor. When in doubt, check the data sheet. ↩︎