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<H1 ALIGN="CENTER">Building your Parallel Port Hardware</H1>
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<P>
These are simplified schematics for the IR hardware
I build some time ago. I have written them down
using some barely readable handwritten notes and
some reverse-engineering. So don't expect this to
really work. Here are some <A
HREF="pictures.html">pictures</A> of this device.
</P>
<P><B>USE AT YOUR OWN RISK!</B></P>
<P>
But if you manage to build this device, drop me a
note. I devided the schematics in three
sections. The first shows the frequency generation
circuit. I use this to generate a 38 kHz carrier
frequency for the IR signals that are sent and a
65536 Hz timer, which is required for both the
transmitter and receiver circuits. The timer helps
me to get the proper software timings, as interrupts
are only generated on the rising edge of the /ACK
signal. It is also handy for sending IR signals
reliably. This shouldn't be really necessary on a
Pentium but this way the device should also work
with an 286. The transmitter and receiver circuits
should be quite self-explanatory. The inverter in
the receiver circuit is only necessary if you use an
active low IR detector IC like the SFH506.
</P>
<P>
Mike Karasoff created a modified circuit based on this
design that allows to use up to <A HREF="http://www.freelancelogic.com/Projects/lirc_pport/lirc_pport_mod.html">8 independent transmitters</A>
with your parallel port.
</P>
<PRE>
Frequency generation:
C1
|| +----------+ +----------+
GND o------||------+------| R1 |------+------| R2 |-----o Vcc
|| | +----------+ | +----------+
| |
+---------+-----------+ |
C2 | | |
|| | | |
GND o------||-------------------------+ | |
|| | | | |
| | | | +----------+
BUSY o------------------------|--+ +--|--|--|------| R3 |-----o Vcc
65536 Hz | | | | | | +----------+
GND o---+ | | | | | |
| | | | | | |
+-+--+--+--+--+--+--+-+
| 7 6 5 4 3 2 1 |
| |
| NE556 |
| |
| 8 9 10 11 12 13 14 |
+-+--+--+--+--+--+--+-+
| | | | | | |
| | | | | | +---o Vcc
| | | | | |
o---------------------|--+ +--|--|--|--------------------------o D0 (*)
38 kHz | | | |
|| | | | |
GND o------||----------------------+ | |
|| | | |
C2 | | |
+------+-----------+ +--+
| |
|| | +----------+ | +----------+
GND o------||------+------| R4 |------+------| R2 |-----o Vcc
|| +----------+ +----------+
C1
Transmitter circuit:
o 38 kHz
|
|
|
|
+---+
| |
| |
| R |
| 6 |
| |
| |
+---+
|
| --->
| ---> D1 (IR LED)
| --->
_|_
/ \ | /| +----------+
GND o------------------ ---------|< |------------| R7 |-----o Vcc
T1 | \| +----------+
Receiver circuit:
GND o------------------------------------+
C3 |
|| | +--------------+
+----||---+---|1 |
+----------+ | || | ========= | <---
Vcc o-----------| R5 |---+-------------|2 SFH506-38 | <---
+----------+ | ========= | <---
+---|3 |
| +--------------+
/ACK o---------------------------------+ |
| |
GND o---+-----+-----+ | |
| | | | |
+-+--+--+--+--+--+--+-+
| 7 6 5 4 3 2 1 |
| |
| 74HC04 (**) |
| |
| 8 9 10 11 12 13 14 |
+-+--+--+--+--+--+--+-+
| | | |
+-----+-----+--+---o Vcc
Part list:
R1 = 22323R
R2 = 2200R
R3 = 4700R
R4 = 39297R
R5 = 330R
R6 = 1000R
R7 = 33R
C1 = 470pF
C2 = 10nF
C3 = 4,7uF
T1 = BC 338
D1 = e.g. LD274 (R7 calculated for forward voltage of 1.3 V)
C2, C3, R5 are optional, but recommended in the datasheets. Vcc is 5 V.
(*) As D0 is an input the circuit always must be connected to the
parallel port. You might also consider adding a pull-down resistor to
GND.
(**) I used a 74LS04 but 74HC04 should be the better choise. Don't
forget to connect the unused inputs to a valid logic level,
i.e. either Vcc or GND.
</PRE>
<P>
The NE556 generates timings with pulses and spaces
according to the following formulas:
</P>
<PRE>
t1=0.693(R2+R1)C1
t2=0.693(R1)C1
</PRE>
<P>
I used a 50 kR and a 25 kR potentiometer for R4 and
R1 to get the correct frequencies.
</P>
<P>
Instead of the inverter IC (74LS04) you can also use
some smarter circuit that will generate an interrupt
for each change of the signal coming from the IR
detector (SFH 506-38). Then the 65536 Hz generated
by the NE556 IC won't be necessary either.
</P>
<P>
The only thing that is missing here is the power
supply. I used an external power supply as AFAIK the
parallel port can not supply the necessary power.
</P>
<P><A HREF="mailto:lirc@bartelmus.de">Christoph</A></P>
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