Tag: geekery

I decided I wanted to have some sort of physical display in the house for the temperature sensors so we wouldn’t need to be taking out our phones to check the temperature on my website if we were already inside at home. After a bunch of searching around, I discovered the PaPiRus ePaper display. ePaper means it’s not going to have any bright glaring light at night, and it also uses very little power.

The Raspberry Pi is hidden away under a side table, and already has six wires attached to the header for the temperature sensors, so I decided to just get a separate Raspberry Pi Zero W — which is absurdly small — and the PaPiRus display.

Setting it up

I flashed the SD card with the Raspbian Stretch Lite image, then enabled SSH and automatic connection to our (2.4GHz; the Zero W doesn’t support 5GHz) wifi network by doing the following:

1) Plug the flashed SD card back into the computer.

2) Go into the newly-mounted “boot” volume and create an empty file called “ssh” to turn on SSH at boot

3) Also in the “boot” volume, create a file called “wpa_supplicant.conf” and paste the following into it:

country=AU
ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
update_config=1
network={
ssid="WIFI_SSID"
psk="WIFI_PASSWORD"
key_mgmt=WPA-PSK
}


4) Unmount the card, pop it into the Pi, add power, and wait 60-90 seconds and it’ll connect to your network and be ready for SSH access! The default username on the Pi is “pi” and the password is “raspberry”.

(These instructions are all thanks to this blog post but I figured I’d put them here as well for posterity).

The PaPiRus display connection was dead easy, I just followed Pi Supply’s guide after soldering a header into the Pi Zero W. If you want to avoid soldering, they also offer the Zero W with a header pre-attached.

Getting the Python library for updating the display was mostly straightforward, I just followed the instructions in the GitHub repository to manually install the Python 3 version.

I wrote a simple Python script to grab the current temperature and humidity from my website’s REST endpoints, and everything works! This script uses the “arrow” and “requests” libraries, which can be installed with “sudo apt-get install python3-arrow python3-requests”.

Next step is to have the Pi 3 that has the sensors run a simple HTTP server that the Zero W can connect to it, so even if we have no internet connection for whatever reason, the temperatures will still be available at home. I’ve updated my Pi Sensor Reader to add HTTP endpoints.

The Weather section on my website is now powered by my Raspberry Pi, instead of my Ninja Block! \o/

Almost exactly three years ago, I started having my Ninja Block send its temperature data to my website (prior to that, I was manually pulling the data from the Ninja Blocks API and didn’t have any historical record of it). Ninja Blocks the company went bust in 2015, and there was some stuff in the Ninja Blocks software that relied on their cloud platform to work and I ended up with no weather data for a couple of days because the Ninja Block couldn’t talk to the cloud platform. I ended up hacking at it and the result was this very simple Node.js application as a replacement for their software. It always felt a bit crap, though, because if the hardware itself died I’d be stuck; yes, it was all built on “open hardware” but I didn’t know enough about it all to be able to recreate it. I’d ordered a Raspberry Pi 3 in June last year, intending on replacing the Ninja Block and it’s sometimes-unreliable wireless temperature sensors with something newer and simpler and hard-wired, but I found there was a frustrating lack of solid information regarding something that on the surface seemed quite simple.

I’ve finally gotten everything up and running, the Ninja Block has been shut down, and I’ve previously said I’d write up exactly what I did. So here we are!

Components needed

• Raspberry Pi 3 Model B+
• AM2302 wired temperature-humidity sensor (or two of them in my case)
• Ethernet cable of the appropriate length to go from the Pi to the sensor
• 6x “Dupont” female to either male or female wires (eBay was the best bet for these, just search for “dupont female”, and it only needs to be female on one end as the other end is going to be chopped off)
• 1.5mm heatshrink tubing
• Soldering iron and solder
• Wire stripper (this one from Jaycar worked brilliantly, it automatically adjusts itself to diameter of the insulation)

Process

1. Cut the connectors off one end of the dupont cables, leaving the female connector still there, and strip a couple of centimetres of insulation off.
2. Strip the outermost insulation off both ends of the ethernet cable, leaving a couple of centimetres of the internal twisted pairs showing.
3. Untwist three of the pairs and strip the insulation off them, then twist them back together again into their pairs.
4. Chop off enough heatshrink tubing to cover the combined length of the exposed ethernet plus dupont wire, plus another couple of centimetres, and feed each individual dupont wire through the tubing (there should be three separate bits of tubing, one for each wire).
5. Solder each dupont wire together with one of the twisted pairs of ethernet cable, then move the heatshrink tubing up over the soldered section and use a hairdryer or kitchen blowtorch to activate the tubing and have it shrink over the soldered portion to create a nice seal.
6. Repeat this feed-heatshrink-tubing/solder-wire/activate-heatshrink process again but with the cables that come out of the temperature sensor (ideally you should be using the same red/yellow/black-coloured dupont cables to match the ones that come out of the sensor itself, to make it easier to remember which is which).
7. Install Raspbian onto an SD card and boot and configure the Pi.
8. Using this diagram as a reference, plug the red (power) cable from the sensor into Pin 2 (the 5V power), the yellow one into Pin 7 (GPIO 4, the data pin), and the black one into Pin 6 (the ground pin).

AdaFruit has a Python library for reading data from the sensor, I’m using the node-dht-sensor library for Node.js myself. You can see the full code I’m using here (it’s a bit convoluted because I haven’t updated the API endpoint on my website yet and it’s still expecting the same data format as the Ninja Block was sending).

I’d found a bunch of stuff about needing a “pull-up” resistor when connecting temperature sensors, but the AM2302 page on adafruit.com says “There is a 5.1K resistor inside the sensor connecting VCC and DATA so you do not need any additional pullup resistors”, and indeed, everything is working a treat!

I decided that the sound output from the Pi’s built-in headphone jack wasn’t sufficient after all and so went searching for better options (a DAC—digital-to-analog converter).

The Raspberry Pi foundation created a specification called “HAT” (Hardware Attached on Top) a few years ago which specifies a standard way for devices to automatically identify and configure a device and drivers that’s attached to the Pi via its GPIO (General Purpose Input/Output) pins. There’s a number of DACs now that conform to this standard, and the one I settled on is the JustBoom DAC HAT. It’s a UK company but you can buy them locally from Logicware (with $5 overnight shipping no less).

The setup is incredibly simple: connect the plastic mounting plugs and attach the DAC to the Pi, then start it up and edit /boot/config.txt to comment out the default audio setting:

#dtparam=audio=on

Then add three new lines in:

dtparam=audio=off
dtoverlay=i2s-mmap
dtoverlay=justboom-dac

Then reboot. (If you’re running Raspbian Stretch or newer, the i2s-mmap line should not be added).

To say that I’m impressed would be an understatement! I didn’t realise just how crappy the audio from the Pi’s built-in headphone jack was until I’d hooked up the new DAC and blasted some music out. I’m not an audiophile and it’s hard to articulate, but I’d compare it most closely to listening to really low-quality MP3s on cheap earbuds versus high-quality MP3s on a proper set of headphones.

If you’re going to be hooking your Pi into a good stereo system, I can’t recommend JustBoom’s DAC HAT enough!