coffee_machine.md

Coffee Machine Project

I'm working on connecting a coffee machine to the internet so it can be turned on and off from a website or from twitter. Raspbian code here.

Current State:

Contents:

• Steps
• Problems
• TODO

Steps:

Raspberry Pi:

Setting Up WiFi

The school wifi can be a bit tricky to use because it uses PEAP authentication. This is the reason why it's difficult to connect an arduino to the network. wpa_supplicant can be used to connect to the network. Here is a nice tutorial. /etc/wpa_supplicant/wpa_supplicant.conf:

...
network={
    ssid="SPS-Secure"
    key_mgmt=WPA-EAP
    eap=PEAP
    identity="username"
    password="password"
    phase2="auth=MSCHAPV2"
}

I tried to export the certificate from my laptop and use it on the raspberry pi but that didn't work. Not including the field ca_cert makes wpa_supplicant ignore the certificate. This is a security risk but it's not a big deal for me rightn now.

It's not safe to store passwords as plaintext so I ran

$ echo -n "password" | iconv -t utf16le | openssl md4

and put the output as hash:output in the password field.

Next, I edited /etc/network/interfaces:

...
auto wlan0
iface wlan0 inet dhcp
    wpa-ssid "SPS-Secure"
    pre-up wpa_supplicant -B -Dwext -i wlan0 -c/etc/wpa_supplicant/wpa_supplicant.conf -f /var/log/wpa_supplicant.log
    post-down killall -q wpa_supplicant

Then I ran

$ sudo ifdown wlan0
$ sudo ifup wlan0

And the WiFi worked.

Monitor Website

This is basically a Python script with a while loop that uses the Twitter API and the urllib module to check Twitter and check the website for states.

Monitor Twitter

I used the Python module Tweepy because it made it easier to deal with the Twitter API. Authentication is made easy, and searching for a hashtag is as simple as

api.search("#spscoffee2k17")

The documentation is here.

Run script at boot

We used systemd to run the python script at boot time. To do this, we created a script in /etc/systemd/system/ called coffee.service. The script looks something like this

[Unit]
Description=Turn on coffee machine based on website or Twitter input

[Service]
EnvironmentFile=/path/to/file/with/env/variables
ExecStart=/path/to/script
Restart=on-failure

[Install]
WantedBy=multi-user.target

The Restart option is very important here because the script needs networking to function, and networking isn't available at system boot time. The script will always fail at first, but it will always restart. This is bad programming design, so I added some error handling logic to the code so that it logs network failures and keeps running through them.

Safety Override

We don't want to burn down the lab just because someone spams a twitter hashtag or inadvertently turns the system on when there's no water in it, so we added a safety override switch. The script keeps track of this variable named loaded. It updates the value to True when someone flips the switch, and to False after it tells the coffee machine to make coffee.

Custom Website

Django is a popular Python web framework (for backends) that I used to create a website. It comes with many features and tools for development. I now know that for a simple website like this, I could have used a lightweight framework like Flask, but Django was a pretty good choice.

The gist of the website is that when you type the right password it lets you click the Brew button which updates a page on the website. The Raspberry Pi is constantly monitoring that page and once it updates the Pi will make coffee.

Problems:

Timezone

I fixed the timezone problem by fully working in UTC.

Persistent Storage

One time the network had some problems in the evening and the script restarted. Prior to this the loaded variable was set to True. The restart made the Pi lose the state of the variable, and someone had to go to the lab to physically press the switch for it to respond to web or Twitter requests. A solution to this is to save the variable to a file so it stays between different sessions. This is achieved with

with open("loaded.state", mode="w") as f:
    f.write(str(self.loaded))

TODO:

• Add button to track if the coffee machine has been prepared
• Persistent storage of the loaded variable state
• Coffee delivery system
• Water delivery system
  • Water level sensor