coffee

RESTful Espresso. coffee consists of three parts:

1. An arduino sketch which communicates with a python server.
2. A python server which communicates with the arduino and provides a REST API.
3. A frontend which consumes the API.

coffee.arduino

coffee.arduino is the arduino app that powers coffee. It is entrusted with turning the boiler and pump on and off and keeping the boiler temperature as near to the target temperature as possible via a pid loop.

You can either use the Arduino IDE to build the project or the Makefile which requires arduino-mk to be installed on your system. If you choose the latter, be sure to edit the makefile to target your board.

Ubuntu Installation Notes

It's pretty simple to get working on Ubuntu, but a few packages are needed.

sudo apt-get install arduino arduino-mk libdevice-serialport-perl

OS X Installation Notes

The arduino makefile is a bit of a pain to install on OS X. All these steps assume you have homebrew set up already. The steps are as follows:

# Install these perl modules for sending serial resets to the board
# You may have to enter the cpan shell and manually set an http mirror
# For example http://serverfault.com/questions/130690/force-cpan-to-download-via-http
sudo perl -MCPAN -e 'install +YAML'
sudo perl -MCPAN -e 'install +Device::SerialPort'

# Add the avr-gcc homebrew tap
brew tap larsimmisch/avr

# Install avr-gcc and avrdude
brew install avr-libc avrdude

# Now we need to install Arduino-Makefile, change the initial cd to install it elsewhere
cd ~/workspace/
git clone git@github.com:sudar/Arduino-Makefile.git
ln -s ~/workspace/Arduino-Makefile/bin/ard-reset-arduino ~/bin/

LM75A Temperature Sensor

coffee uses the LM75A I2C temperature sensor. It can be found cheaply online, does not require an external thermocouple or amplifier and works within the range of temperatures needed to make coffee and steam. It is a bit slow for conventional PID applications, but since our boiler will have lag time anyway from the fact that it is a big hunk of brass, this doesn't matter in practice.

Addresses for the LM75A are determined by whether pins 5, 6 and 7 are tied high or low. The first four bits of the address are hardcoded into the chip as 1001. The three least significant bits represent the rest of the address. Tying a pin to Vs+ makes it 1, to ground makes it 0. In my setup it was easiest to tie them all to Vs+ since they are next to each other, which makes my address binary 1001111, or int 79.

To figure out the integer address of your LM75A, tie your pins either high or low, and run echo "ibase=2;1001111" | bc replacing your address in binary.

A good datasheet for the LM75A is provided by Texas Instrument which I have mirrored in this repo.

coffee.server

coffee.server is the server component that communicates between the arduino and exposes a REST API for making coffee and steamed milk.

coffee.frontend

A refernce frontend for coffee.server, coffee.frontend is meant to be run at http://coffee and provides a full featured html frontend for the coffee server.

iDevice Serial Cable

A special serial cable needs to be constructed to communicate with the Arduino over serial. Since the Arduino I'm using outputs its signal at 5v, we need to step the voltage down from Arduino TX to iDevice RX. A simple way to do this is with a voltage devider using two 1k ohm resistors.

Ground ---
         |
  <1k Ohm Resistor>
         |
Arduino Tx @ 5v ---< 1k Ohm Resistor >--- iDevice Rx (pin 13)

Arduino Rx ------------------------------ iDevice Tx @ 3.3v (pin 12)

My testing cable looks like this, labeled from left to right:

* pin 27 - green - USB Data+
* pin 25 - white - USB Data-
* pin 23 - red   - +5v
* pin 16 - black - USB Ground
* -------------------------------
* pin 13 - green - Serial Rx
* pin 12 - white - Serial Tx 3.3v