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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 -
~Strobe
       ____________________________________________________________
      /                                                            \
      \     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:


                             Vcc
                              |
                              +------+
                              |    __|__
                            Relay   /^\  Diode 1N4002
                             Coil  /---\
                              |      |
                              +------+
                              |
                           | / 
                 4.7K    B |/  C
parallel port >-\/\/\/\/---|        NPN Transistor: BC547A or 2N2222A
data pi                    |\  E
                           | \
                             V
parallel port >--------------+
ground pin                   |
                          Ground

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
                                                LOAD

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


+5VDC
|    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
             \
              V
              |
             ---
            ///

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.


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