# COFFEE-HOWTO: Electronic circuit

## 2. Electronic circuit

A general diagram is like this:

``` --------- 0-5V --------- ~220V ---------------- | PC |==<==>==|Circuit|=========|Coffee-Machine| --------- --------- ~110V ---------------- ```

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

You must choose a Relay circuit, if you have a big coffee-machine (greater than 200W or so), otherwise you can use a triac-based one.

All circuits presented are at least once tested, but it's YOUR RESPONSIBILITY to test the results. If you have no experience with electronics you should NOT experiment with these, otherwise you may get electrocuted.

You should be very careful while experimenting with 120/220V, and there is no obsolence in using an appropriate fuse.

## 2.1 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 Male DB-25 Connector +- Pin 13 +- Pin 12 +- Pin 11 +- Pin 10 - ACK -+ +- Pin 9 - D7 -+ +- Pin 8 +- Pin 7 +- Pin 6 +- Pin 5 | | | | | | | | | +- Pin 4 | | | | | | | | | | +- Pin 3 | | | | | | | | | | | + Pin 2 - D0 | | | | | | | | | | | | + Pin 1 - ~Strobe | | | | | | | | | | | | | v v v v v v v v v v v v v ____________________________________________________________ / \ \ 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 / <-- ground (Except 14 - 17) \______________________________________________________/ ^ ^ ^ ^ | | | | Pin 14 - AutoFd -+ | | | Pin 16 - Init -+ | | Pin 15 - Error -+ | Pin 14 - Select -+ Back View Mail Centronics Connector ________________________________________________________________________________ / \ \ / \ ]========================================================================[ / \ / \__________________________________________________________________________/ ```

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 ```

## 2.2 Controlling with a Relay

The simplest circuit that somebody can build is:

``` Vcc | +------+ | __|__ Relay /^\ Diode 1N4002 Coil /---\ | | +------+ | | / 4.7K B |/ C parallel port >-\/\/\/\/---| NPN Transistor: BC547A or 2N2222A data pin |\ 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 reasonable for your coffee-machine.

Barmen, usually, tend to put the relay AFTER the transistor, at the emitter (E) pin instead of the collector (C) pin. This is a bad practice because it biases the transistor badly, and may 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 become darker and smelling...

## 2.3 Controlling with TRIAC #1

If you only want a simple circuit, you can use Motorola's triac driver MOC301012, together with a general purpose TRIAC like SC141D. This method has the advantage that you don't need an 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, use a 3021 instead. Inductive loads should be used in conjuction with bypass capacitors, see Motorola Application Note AN-780. Coffee-machines are mainly resistive loads and not inductive (like a motor), but who knows what yours is...

## 2.4 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 | --- /// 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 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 w/o applying AC and a load. Note the 500V rating on the .01 cap.