Garden Logger Schematic and Voltage Divider Script

There are a few features I want to add to the Garden Logger, but now the wiring's getting complicated. I'm adding three soil moisture sensors, a battery voltage measurement circuit, a voltage reference, and an LED with an annunciator. I need to use a CAD tool to draw the schematic, so I tried gEDA Schematic Editor. It's pretty easy to use and there is a library of user generated parts. You can also easily generate your own parts and modify existing ones. I used the symbol editor to create a soil moisture probe and a temperature/humidity sensor. Once you've created the symbol, you have to move it to /usr/share/gEDA/sym/local. 

For the battery voltage measurement circuit, I needed to calculate what resistor values to use for the voltage divider.  I wrote a little script to calculate this, and in the process found a neat library called "engineering_notation". The library makes it easy to display values in powers of three using the correct SI notation. 

Here are the results:

Enter input voltage: 15
Enter output voltage: 5
Enter current in mA: 1

r1 value => 10kΩ
r2 value => 5kΩ
voltage  => 5.0 volts
current  => 1.0 milliamps
r source => 2.50kΩ
r1 power => 10.0 milliwatts
r2 power => 5.0 milliwatts

Web Server for the Garden Logger

I'd like to be able to see how the Garden Logger's doing. Is it still running? What values is it reading now?

I'd like to stick a Raspberry Pi in the bento box with the Arduino, run a web server on the Pi, and have have the Pi serve up web pages showing the logger's status;  and maybe even control which channels are scanned at what speed.

I was going to develop it on a Pi Zero W, using VSCode via SSH. No dice -  VSCode didn't support the Pi Zero's Processor. Same thing with RasPi 2. It does work with a RasPi 3, but I didn't have any to spare, so I wrote the code on my Linux Mint workstation.

I thought it would be great if logger could send a nice JSON package across to the Pi, but it was better to keep things simple on the Arduino and to put those smarts into the web server. So for now, every time the Arduino writes data to the SD card, it also sends a string of data channel names followed by a string of the data from those channels.

The first thing to do is to install the serial and web server libraries. For some reason, I needed to "pip uninstall" the serial library, then "pip install" the pyserial library. I "pip install"ed the Flask library for the web server.

After connecting the Arduino to a USB port, the sever app needs to find the port that the Arduino's attached to. This is the code snippet I used. It's hard coded to use a specific "Seeeduino", so the process is that the list of hardware IDs needs to be printed using the first two lines in the code snippet, then after the right ID is determined, it gets hardcoded into the server app.

for port in list(list_ports.comports()):

print(port.hwid)

if port.hwid.startswith('USB VID:PID=0403:6001'): # change this if using something other than Seeeduino.

print('Arduino on: ' + port.device)

arduinoPort = port.device

I used this tutorial as a starting point for learning Flask

After I got the example working I needed to start a thread running that would wait asynchronously for data from the Arduino, then parse it, and save it into a global variable for the web server.

print('starting data acq')

dataAcq = threading.Thread(target=monLogger)

dataAcq.start()

The next step was to start the web server. Here's where I hit a problem. When I started it in the VSCode IDE, it was bringing up a second instance of the logger monitor thread. I was really stumped until I came across a web posting that said debug must be disabled on the server. I changed that, and the problem was fixed!

print("starting server")

app.run(debug=False, host='0.0.0.0') # debug=False should prevent restart and doubling dataAcq

Now the final step was to get the data into a Jinja2 template for display. With a few more lines of code, I can now monitor the Garden Logger from anywhere on my network!

Adding an External Hard Drive with Samba to a Raspberry Pi

I started with an out-of-the-box 4TB Western Digital Blue drive. I put it into a Sabrent enclosure, powered it up and plugged it in. First step is to find the drive:

pi@raspberry:/mnt$ sudo lsblk -o UUID,NAME,FSTYPE,SIZE,MOUNTPOINT,LABEL,MODEL
UUID                                 NAME        FSTYPE  SIZE MOUNTPOINT LABEL  MODEL

                                     sda                 3.7T                  WDC_WD40EZRZ-22GXCB0
                                     mmcblk0             3.7G                   
4AD7-B4D5                            ├─mmcblk0p1 vfat    256M /boot      boot   
2887d26c-6ae7-449d-9701-c5a4018755b0 └─mmcblk0p2 ext4    3.4G /          rootfs 

Now to format it:

pi@raspberry:/mnt $ sudo mkfs.ext4 /dev/sda

Create a directory:

pi@raspberry:/mnt $ sudo mkdir /mnt/ext_storage

Mount the drive in the directory:

pi@raspberry:/mnt $ sudo mount /dev/sda /mnt/ext_storage

Reboot:

pi@raspberry:/mnt $ sudo reboot

You'll get kicked out. Login again.  Verify that it's mounted:

pi@raspberry:/mnt/ext_storage $ sudo lsblk -o UUID,NAME,FSTYPE,SIZE,MOUNTPOINT,LABEL,MODEL

UUID                                 NAME        FSTYPE  SIZE MOUNTPOINT       LABEL  MODEL

7dd94502-35a2-4bd3-a218-7cf76e350c7b sda         ext4    3.7T /mnt/ext_storage        WDC_WD40EZRZ-22GXCB0

                                     mmcblk0             3.7G                         

4AD7-B4D5                            ├─mmcblk0p1 vfat    256M /boot            boot   

2887d26c-6ae7-449d-9701-c5a4018755b0 └─mmcblk0p2 ext4    3.4G /                rootfs 

pi@raspberry:/mnt/ext_storage $ sudo blkid

/dev/mmcblk0p1: LABEL_FATBOOT="boot" LABEL="boot" UUID="4AD7-B4D5" TYPE="vfat" PARTUUID="80a50d6c-01"

/dev/mmcblk0p2: LABEL="rootfs" UUID="2887d26c-6ae7-449d-9701-c5a4018755b0" TYPE="ext4" PARTUUID="80a50d6c-02"

/dev/sda: UUID="7dd94502-35a2-4bd3-a218-7cf76e350c7b" TYPE="ext4"

/dev/mmcblk0: PTUUID="80a50d6c" PTTYPE="dos"

Now set up Samba:

sudo chown pi /mnt/ext_storage

sudo apt-get update

sudo apt-get install samba samba-common-bin

sudo nano /etc/samba/smb.conf

[ext_storage]

path = /mnt/ext_storage

writeable=Yes

create mask=0777

directory mask=0777

public=no

sudo smbpasswd -a pi

sudo systemctl restart smbd

After doing the above, I had a few issues. First, the external hard drive wasn't remounting when the Pi was rebooted. To fix this. I added the following to /etc/rc.local:

sudo mount /dev/sda /mnt/ext_storage

Next, some directories like the user home directory and the non-existent printer directories were showing up on some Samba clients like Macintosh and AppleTV VLC Player. The solution was to comment out the following sections in /etc/samba/smb.conf:

[home]

[printers]

[print$]