Coffee Making

Fotis Georgatos < [email protected]>

V1.0 2004-08-29

One of the most memorable comments about software ever said is whether this or that piece of code can make coffee. Coffee is a world commodity that is second only to oil. Linux DOES make coffee; and it tastes good as well!

1. Introduction

2. Menu

3. Hardware

4. Software

5. Building the Turing Complete Coffee Machine

6. Overdose symptoms

7. Expansions

8. Further Information

1. Introduction

For a long time humanity has been wondering how could a computer make coffee...

People need coffee to wake up, and stay awake for a long time in front of the computer. It is common wisdom that coding is better at night!

The main trick is interfacing a coffee machine to the computer, so that it can be controlled by software. This HOWTO will show you how to do so.

At first, it demonstrates an ON/OFF switch implemented as an electronic circuit which controls the coffee-machine's power supply. Another chapter will tell you the secrets of building intelligent, Turing Complete suitable, coffee machines!

This HOWTO was initially written as part of a debate in the mailing list linux-greek-users, on whether linux can make coffee or not. It then became an article in our online magazine called magaz. Just in case you wondered, magaz is in Greek and it will surely look like that to you!


1.1 Copyright

Copyright © 2004-08-29 by Fotis Georgatos. You are free:

Under the following conditions: Attribution. You must give the original author credit. Share Alike. If you alter, transform, or build upon this work, you may distribute the resulting work only under a license identical to this one.

1.2 Disclaimer

Use the information in this document at your own risk. I disavow any potential liability for the contents of this document. Use of the concepts, examples, and/or other content of this document is entirely at your own risk.

All copyrights are owned by their owners, unless specifically noted otherwise. Use of a term in this document should not be regarded as affecting the validity of any trademark or service mark.

Naming of particular products or brands should not be seen as endorsements.

You are strongly recommended to take a backup of your system before major installation and backups at regular intervals.

1.3 Version

The Coffee HOWTO is now called Coffee Making HOWTO and heads for release v1.0, which will first appear somewhere here:

It is about time for everyone to know that Coffee Making is just one of the standard features that come for free with *any* Linux distribution. Or, does SCO have a patent on that, too? Gee...

1.4 Translations

You should be able to easily find a translation of this or previous versions of the Coffee Making HOWTO in the following languages:

and hopefully many more... (Spanish and Portugeuse anyone?)

1.5 Credits

1.6 What do you drink/smoke while writing this?

Well, to the best of my knowledge, this is a dope-free work.

But, I can tell you the secret of the music playing on the background: nearly any song spelled by Zampetas or Mpithikotsis (bouzouki and such).

1.7 Feedback

For your online commentary of your own DIY Coffee Machine steer at

If you still have comments to say, emails get lost these days, so why not send me a postcard with a picture from your great hometown, adding a recommendation of your favourite cafe' in the area?

Fotis Georgatos, 
Aliartou 32, 
TK 11142 Athens, 


2. Menu

2.1 French

Popular coffee among programmers because it doesn't need a lot of care and its cooking is streamlined; just like commercial software. Its exciting taste has inspired thousands of programmers in writing incredible software, written in the very first hours of a day. M$ Windows for example has been written at 5:00 o'clock in the morning, only thanks to coffee! A similar result is guaranteed.

2.2 Nescafe

Nescafe is a rather strong coffee, made by pouring hot water in a mixture of coffee, sugar and some water. You usually take 1 spoon of coffee and 1 spoon of sugar with just a bit of water, to mix it. In the meantime you should have the water boiling. As soon as the water is hot enough, you mix them all together and preferably add condensed milk. Although you could use something simpler than a coffee-machine to boil the water, I have seen this done so several times...

2.3 Frappe'

A popular variation of the above mentioned coffee. Actually, you don't need a sophisticated coffee-machine, rather a refrigerator for cold water and ice-cubes. It is very popular in South Eastern Europe during the warm summer months.

2.4 Freddo

This is a complicated one, read coffee-faq (read further information)

2.5 Espresso

Espresso is a very strong, italian sort of coffee. You serve it in small cups (You ask why? See chapter: Overdose Symptomes) with one or two pieces of lump sugar. To produce a good espresso you need fresh grinded coffee beans, water, lump sugar and a special machine. These machines boil the water and press the very hot steam through the grinded coffee beans. You can buy a super-duper-automatic machine for a lot of money. But a low cost machine is usable, too.

OK., lets start. Fill water in your machine. Let it become hot. In the meantime fill about 1 teespoon of coffeepowder in the filterhandle of your machine. Press the coffeepowder down. Not too much. Now the water is at the right temperature. Attach the filterhandle to the machine and let the machine work. After about 30 seconds you can serve a delicate, hot espresso. It is fine after a good meal. You feel good and can code for a few more hours.

2.6 Cappuccino

(See also chapter: Espresso) If you have a more profi-like machine, you can use it, to froth milk with it. You need this feature to make a creamy sort of coffee. It is easy to prepare. Put some frothed milk in a coffee pot and fill it up with espresso. Then decorade with some chocolade flakes. That's it.

3. Hardware

A generic diagram could look like this:

---------   0-5V  ---------  ~220V   ----------------
|  PC   |====>====|Circuit|==========|Coffee-Machine|
---------         ---------          ----------------

The concept is that we take a controling voltage from the computer, which drives an electrically isolated circuit with a Relay or Triac.

You must choose a Relay circuit, if you have a coffee-machine greater than 200W. You can use a triac-based one if your coffee machine isn't high power.

All circuits presented are tested, but the results and risks are YOUR OWN RESPONSIBILITY. If you have no experience with electronics you should NOT try building it on these, otherwise you may get a bad one...

You should be very careful while experimenting with 220V, and using an appropriate fuse is absolutely advisable.

3.1 Driving voltage 0-5V from the computer

Here is a simple example to get a voltage 0-5V from the parallel port of the computer.

      Back View          -----    Pin 10 - ACK
      Male DB-25         |   |    Pin  9 - D7
      Connector          |   |                           Pin 2 - D0
                         v   v                           v   Pin 1 -
      /                                                            \
      \     13  12  11  10   9   8   7   6   5   4   3   2   1     /
       \                                                          /
        \     25  24  23  22  21  20  19  18  17  16  15  14     /

Pin 1 is Strobe (inverse logic)

Pins 2-9 is DATA BUS's signals, exactly what was written to the parallel port's latches with an OUTB command.

Pin 10 is the acknowledge signal (ACK), controlled by you, so that you can produce an interrupt to the CPU.

Pins 18-25 are short-circuited and this is the ground (GND).

In detail:

<= in   DB25    Cent    Name of         Reg
=> out  pin     pin     Signal          Bit     Function Notes
------  ----    ----    --------        ---     -----------------------------
=>       1       1      -Strobe         C0-     Set Low pulse >0.5 us to send
=>       2       2      Data 0          D0      Set to least significant data
=>       3       3      Data 1          D1      ...
=>       4       4      Data 2          D2      ...
=>       5       5      Data 3          D3      ...
=>       6       6      Data 4          D4      ...
=>       7       7      Data 5          D5      ...
=>       8       8      Data 6          D6      ...
=>       9       9      Data 7          D7      Set to most significant data
<=      10      10      -Ack            S6+ IRQ Low Pulse ~ 5 uS, after accept
<=      11      11      +Busy           S7-     High for Busy/Offline/Error
<=      12      12      +PaperEnd       S5+     High for out of paper
<=      13      13      +SelectIn       S4+     High for printer selected
=>      14      14      -AutoFd         C1-     Set Low to autofeed one line
<=      15      32      -Error          S3+     Low for Error/Offline/PaperEnd
=>      16      31      -Init           C2+     Set Low pulse > 50uS to init
=>      17      36      -Select         C3-     Set Low to select printer
==      18-25   19-30,  Ground

3.2 Controlling with a Relay

The straight-forward circuit one can build is:

                              |    __|__
                            Relay   /^\  Diode 1N4002
                             Coil  /---\
                              |      |
                           | / 
                 4.7K    B |/  C
parallel port >-\/\/\/\/---|        NPN Transistor: BC547A or 2N2222A
data pi                    |\  E
                           | \
parallel port >--------------+
ground pin                   |
Connect Vcc with the same voltage as the relay type (usually 5 or 12V). Obviously, the relay's specifications should be scaled for your coffee-machine.

Barmen, tend to put the relay AFTER the transistor, at the emitter (E) pin instead of the collector (C) pin. This is bad practice because it biases the transistor badly, and might result in bad coffee :-). Diode 1N4002 is useful to protect the transistor from the relay's currents. If you don't use it the transistor will sooner become dark and smelly...

3.3 Controlling with TRIAC #1

If you only want a simple circuit, you can use Motorola's triac driver MOC301[012], together with a general purpose TRIAC like SC141D. This method has the advantage that you don't need any extra power supply.

For non-inductive loads, this is the circuitry:

        270     1 +-------+ 6    180
  +5v -VAVAVA-----+       +----VAVAVA-----+-------------- Line Hot
                2 |  MOC  |               |
  TTL in ---------+ 3012  +nc            VA  SC141D
                  |       | 4           / |
                nc+       +------------/  |
                  +-------+               +----\/\/\/---- Line Neutral

If you are going to work with 220V, try to obtain a 3021. Inductive loads should be used in conjuction with bypass capacitors, better consult Motorola Application Note AN-780. Coffee-machines are mainly resistive loads and not inductive (like a motor), but who knows what yours is?

3.4 Controlling with TRIAC #2

|    180                      180            2.2k
+---/\/\/\----+-----+   +----/\/\/-+--/\/\/\---+-------> 120V
              |    1|   |6         |           |         Hot
              |    +=====+         |           | MT1
              |    | MC  | TRIAC   |          +-+
              |    | 3032| Driver  |        G | | TRIAC
              |    +=====+         |         /| |
              \    2|   |4         |        / +-+
       2N3904  |----+   |          |        |  | MT2
              /     |   +--------- | -------+  |
             V      \              |        |  |
             |      /              |        \  |
             |      \ 43    .01u  ---   10k /  |
             |      /       500V  ---       \  |
             |      |              |        /  |
             +------+              |        |  |            Neutral
             |                     +--------+--+---o    o--> 120V
             /                                      load
 >-/\/\--|  2N3904

This design is for 120V. You should change resistors accordingly for 220V.

Circuit description:

The MC3032 is an optoisolator TRIAC driver. The 180-ohm resistor sets the current for the LED emitter in the optoisolator. Change the value of this resistor - if necessary - to get a reasonable current (e.g., 15 mA).

Note that you cannot test this circuit without a load. The TRIAC will not switch unless connected to an AC voltage source, so you can't test it for simple switching without applying AC and a load. Note the 500V rating on the .01 capacitor.

4. Software

4.1 Programming

You will have to build an executable that will take the following steps:

Change BASE = 0x3bc for /dev/lp0, 0x378 for /dev/lp1, and 0x278 for /dev/lp2; range=8.

It would be useful if you had that program setuid, so that everybody can drink coffee! You BOFH!

4.2 Device driver

Just read kernel hacker's guide, to implement a device driver; you might also do it in user space. Please compile it as a module, so that we won't need a kernel compile in every update. Then write:

echo cappuccino >/dev/coffee

And you will have a hot cup of coffee in minutes! Remember to give the right permissions to /dev/coffee, depending on whether you want only root making coffee or not.

The advantage of this method is that it supports feedback from the coffee-machine by using the ACK of parallel port and such, so that smart coffee-machines can produce an interrupt when ready.

Do it yourself, after reading the excellent book of Alessandro Rubini and Jonathan Corbet Linux Device Drivers and studying the Cross Reference Linux source code repository.

4.3 Connecting with the Internet

If you have implemented the controlling program in C (see above), you just have to write a CGI script to turn ON and OFF the coffee-machine or pass along more complex instructions. You should write some nice webpages, explaining how to make coffee, and put them on an apache web server...

...LAMP technology (Linux, Apache, MySQL, [Perl|Python|PHP]), will help you to build a perfect user-customizable coffee system!

At some time in the future when the applications get rather complex, you might want to extend on the basis of Flow-Based Programming: What a great match for a great Coffee Machine!

5. Building the Turing Complete Coffee Machine

Do you pine for the nice old days, when men were men and build their own coffee machines?

This chapter is about assembling a smart, intelligent!, coffee machine. It will be a computer designed with a von Neumann architecture, comprised of a CPU, ROM/RAM and I/O and will also be suitable for generic use, a.k.a. Universal Turing Machine.

5.1 An adequate assembly language

Unlike other complex, but popular, systems that are either CISC or RISC, our machinery will be MISC: Mono-Instruction Set Computer!

Alas, our processor will understand just one command and yet, given enough memory and time, it is able to perform any action that your 3GHz Pentium IV could do, or just simulate it alltogether; It can solve any computable problem by running simple code like this:

SBN     $mem1, $addr1
SBN     $mem2, $addr2
SBN     $mem3, $addr3
SBN     $mem4, $addr4
SBN     $mem5, $addr5
SBN     $mem6, $addr6

The magic command is called SBN $mem, $addr (Subtract and Branch if Negative), and does take the value of a memory cell $mem, subtract it from the accumulator (A is the only available register in this architecture) and store it back to the accumulator and memory $mem : [mem] <= A <= A-[mem]. If the result is negative, and only then, it jumps to the designated address $addr. If $addr points to the next command, there is no conditional jump. Now, with that command at hand you can subtract, add, zero memory addresses, move bytes around, multiply, compare and so on, so forth. What's best of all, you can easily build an optimizing compiler.

Voila. This is a great system for any Turing Complete problems plus, it is even simpler in coding than the original Turing Machine!

5.2 Hardware and interfacing

The great thing with this innovative MISC processor is that you need 0 bits to store the opcode of your commands. This makes your CPU much, much simpler: you only have to read a couple of operands each time. You might wish to extend the capabilities of your processor by extending the SBN instruction to 3 or 4 operands, so that it can directly load and store data from main memory. This is an exercise left to the reader; kudos to google.

The CPU diagram looks like this:

<========= ADDRESS BUS ==============>
        =                =
        =  +---------+   =
        =  | CONTROL |   =
   +---------+  +-----------------+
   | ALU & A |  | Program Counter |
   +---------+  +-----------------+
        =  |  LOGIC  |   =
        =  +---------+   =
        =                =
<=========== DATA BUS ===============>

Now, all you have to do is just hook together some memory chips, for example by recycling static cache RAM from old 386 PCs, an ALU and a few glue components. You may pick one of TTL or CMOS for logic gates and latches; I'm a CMOS guy, but this really depends on your favourite flavor. You may build an 8, 16, 32, 64 bit or whatever width system you need. Just in case, for larger word widths, I have found preferable building the ALU with pre-programmed 27128 EPROMS instead of the harder-to-find 74x181s. Look around for a carry propagation unit, too.

The monolithic nature of this system allows only memory-mapped I/O, and requires special design provisions for bidirectional interfacing, but nothing more peculiar than what is seen in older-generation systems. AGC, the computer that drove Apollo 11 mission to the moon was making use of such techniques, so it should be sufficient in this case, too.

Note that the data bus has to be exactly as wide as the address bus, that implies that the notion of a byte is only applicable to 8 bit coffee machines, which you will eventually find that it is more of a feature than a bug. You will be surprised with what a coffee you can have for 8 or 16 bits bus! It is really a general-purpose piece of hardware, built for peanuts.

5.3 Software

Such a pure system will make a good fit together with the, famous for embedded systems controlling, FORTH programming language. The major prerequisite for doing so is to have a stack mechanism, which in this case can be constructed by a counter combined together with a memory pool.

If you want to claim a serious coffee development platform, C portability is an absolute must nowadays. Your choices might be hacking one of gcc, lcc or sdcc, which with proper tweaking at the back-ends will be able to spit out the specially crafted MISC assembly code. One day you might even want to rewrite another language like C, forget the D letter - it is taken already, so do not make again the same mistakes with your compiler please:

Just in case you thought of writing your own compiler, please read in advance about flex, yacc and just a little bit of related theory. In particular you will quickly appreciate Noam Chomsky's taxonomy on languages:

so on, so forth. Read ahead on Computability Theory.

5.4 A minor criticism on the Turing Machine

Because of the way a Turing Machine works (see for that ), it is a very complicated device to program, and debug at the end of the day. The reason is, that its behavior is a sequential process that is completely determined by the following parameters:

The major contemporary disadvantage of the Turing Machine (TM) is that it is of sequential nature, which implies that only a particular range of problems can be mapped to it in a straightforward way. TMs are suitable for problems that are described well on a serial storage medium (tapes) and don't make use of indexes for data reference. This is in contrast to the Coffee Machine (CM) that can handle any Random Access algorithms as well (with no compromise of simplicity).

Add to this, that TMs impose a very high and unnecessary complexity on item (3) in favor of keeping (1) and (2) simple. And just in case you don't agree that the so called Table of Instructions gets trully overwhelmed, have you ever tried to write a compiler for a Turing Machine? A system that isn't easily programmable and is hard to debug, should be considered a seriously questionable system, at least as far as Computer Engineering (!= CS) is concerned. For instance, try to simulate the Coffee Machine with a Turing Machine and vice versa. Hey, if you still disagree, show me the code.

Bottom Line: The Coffee Machine (CM), is a much better model for the von Neumann architecture and has a O(1) relationship with what is standard practice of weighting algorithms, in the current form of complexity theory.

6. Overdose symptoms

7. Expansions

8. Further Information

The list of links in this chapter, often becomes outdated, therefore you might wish to use the excellent Way-Back Machine to find them again: