Parallel port I/O module

Get 5 inputs and 8 outputs from a computer printer port using only a few transistors and resistors.

Details

With this unit a regular computer parallel (printer) port will give you 5 inputs and 8 outputs to use for something fun. And it’s very simply to build; one transistor and one resistor per output, and a single resistor for each input.

The parallel port is pretty simple to access in most programming languages. The module has a 36 pin Centronics connector, making it easy to connect to the computer using a regular printer cable.

By connecting the module to the parallel port of a Linux server, and using some scripts, signals and alarms can be triggered. Making it possible to create a Linux server status panel.

With a web server you can set up a PHP website controlling your module, and with your cell phone you can access this site. But I’ve only managed to use the outputs in Linux.

I’ve even made a data sheet for this module: MJ-8050.pdf

Inputs

The parallel port has 5 status pins that can be used as inputs by pulling them low with a 120 ohm resistor to ground. Some experimentation might be needed as not all the status pins have the same behavior with regards to high and low state.

Outputs

The parallel port also has 8 data pins with TTL-level, meaning active 5V and inactive 0V. Using an NPN transistor with a 4.7K resistor will give you a open collector output. Each output has an LED indicator.

Some history

This was the first computer controller I/O module I built. I originally made it in a wooden box; with LEDs in the front, a xenon strobe on top, and car relays on the back.

I got the schematics and QBasic code on a Usenet newsgroup, and used salvaged parts. Unfortunately I don’t have any photos of it, and I don’t exactly remember what year this was. But I think it in my last years on primary school, so probably around 1995 or 1996.

In 2002 I moved the “electronics” (if you can call it that 😛) into a new enclosure, replaced the LEDs and removed the relays.

The module has been used in multiple projects over the years, like my wooden rack and the rack box.

I/O

Terminal connectors

1. Output 1
2. Output 2
3. Output 3
4. Output 4
5. Output 5
6. Output 6
7. Output 7
8. Output 8
9. Input 1
10. Input 2
11. Input 3
12. Input 4
13. Input 5
14. When-on
15. +12V
16. 0V

Parallel port

DB-25 pin-out

The data pins (D0-D7) are outputs, and the status pins (S3-S7) inputs. The green pins (18-25) are ground. See table below for details.

DB-25 to Centronics

Bash scripts

Life-signal

Done every 5 minutes, using crontab, and sends a signal to a monitoring unit. One 0.5 second pulse is sent to binary address 8.

/var/www/ctrl_files/set_port 1 8 0.5 0.5 > /dev/null

Reset alarm

Sends life-signal to a monitoring unit and closes additional alarm outputs.

/var/www/ctrl_files/turn_port 1 0 > /dev/null
/var/www/ctrl_files/turn_port 2 0 > /dev/null
echo "signal closed to ltcu"
/var/www/ctrl_files/set_port 1 8 0.5 0.5 > /dev/null
echo "life-signal sent to mmu"

Turn port

Turns an output on or off.

PORTSTATUS=`cat /var/www/ctrl_files/port_status`
PORTSTATUSBIT=`cat /var/www/ctrl_files/$1`
let ON=PORTSTATUS+$1
let OFF=PORTSTATUS-$1

if [ $2 -eq 0 ]
then
  if [ ! $PORTSTATUSBIT -eq $2 ]
  then
  echo $OFF > /var/www/ctrl_files/port_status
  echo $2 > /var/www/ctrl_files/$1
  /usr/sbin/parout $OFF > /dev/null
  echo "$1 off"
  fi
fi

if [ $2 -eq 1 ]
then
  if [ ! $PORTSTATUSBIT -eq $2 ]
  then
  echo $ON > /var/www/ctrl_files/port_status
  echo $2 > /var/www/ctrl_files/$1
  /usr/sbin/parout $ON > /dev/null
  echo "$1 on"
  fi
fi

Set port

Gives a pulse on an output.

COUNTER=0
while [ $COUNTER -lt $1 ]; do
  let COUNTER=COUNTER+1
  PORTSTATUS=`cat /var/www/ctrl_files/port_status`
  let ON=PORTSTATUS+$2
  echo $ON > /var/www/ctrl_files/port_status
  /usr/sbin/parout $ON > /dev/null
  echo "$2 on"
  sleep $3
  PORTSTATUS=`cat /var/www/ctrl_files/port_status`
  let OFF=PORTSTATUS-$2
  echo $OFF > /var/www/ctrl_files/port_status
  /usr/sbin/parout $OFF > /dev/null
  echo "$2 off"
  sleep $4
done

Web ping

Gives visual alarm if the ping is higher then 400ms, and sound alarm if above 800ms. If no reply then the “internet failure” alarm will sound.

WEBPING=`ping -c 10 -W 10 catch.no |grep rtt |awk -F '/' '{print $5}' |sed -e 's/time=//' |sed -e 's/\.[0-9]*//'`
PORTSTATUS=`cat /var/www/ctrl_files/port_status`
MAXPING=400
OVERPING=800

if [ $WEBPING ]
then
  echo $WEBPING > /var/www/ctrl_files/ping

  if [ $WEBPING -gt $MAXPING ]
  then
    /var/www/ctrl_files/set_port 1 2 3.6 0.5 > /dev/null
    if [ $WEBPING -gt $OVERPING ]
    then
      /var/www/ctrl_files/set_port 1 16 0.75 0.25 > /dev/null
    fi
  fi

fi

if [ ! $WEBPING ]
then
  /var/www/ctrl_files/turn_port 2 1 > /dev/null
  /var/www/ctrl_files/set_port 3 16 0.25 0.25 > /dev/null
  echo "failed" > /var/www/ctrl_files/ping
  fi

PHP Script

Controlling the Parallel I/O module using php and GPRS.

if(isset($Lamp)) {
echo "<b>Lamp signal sent to LCU.</b><br>";
$output = shell_exec('/var/www/ctrl_files/set_port 1 32 1.5 0.5'); }

Software

The first program I made to control this module was in QBasic, but I don’t have any screenshots or code from that unfortunately.

DVC

DVC Port Kontroll (port control) was written in Pascal using Delphi. It was pretty simple, it could control the outputs, read the inputs, and had a simple security system functionality. I don’t really remember much about it, or why it was called DVC 😛

HEBO

HEBO was a collaboration between myself (hebron) and a friend (bonedawg). It was written in Visual Basic and allowed the parallel port to be controlled using network socket.

Socket communication with the I/O module, through HEBO:

• Read output byte value
• Read input byte value
• Set output byte value

READ &H378
READ: &H378 255

READ 889
READ: 889 127

WRITE &H378 5
WRITE: &H378 5 5

Web and WAP

My very first IoT attempt used the parallel I/O module, PHP and some bash scripts. It wasn’t pretty, but it kind of worked.

Photos

Server status

Rack box

Schematic drawing

Parts used

• 1 × Centronics, chassi, 36-pin
• 1 × Enclosure, plastic (1591 FL), 150x80x50mm, flange
• 1 × LED 3mm, Green, 2.1V, 20mA, 3.5mcd, 38°
• 8 × LED 3mm, Red, 2.1V, 20mA, 1.0mcd, 38°
• 1 × LED 3mm, Yellow, 2.0V, 20mA, 2.5mcd, 38°
• 10 × LED holder 3mm, Chromed metal
• 5 × Resistor, carbon film, 0.25W, 120 Ω, 5%
• 8 × Resistor, carbon film, 0.25W, 4.7 kΩ, 5%
• 10 × Resistor, metal film, 0.6W, 1 kΩ, 1%
• 2 × Switch, toggle, 1-pole, micro, on-on
• 16 × Terminal block, screw, 2.5 mm
• 8 × Transistor, NPN, 100 mA, 45V, 0.5W, BC547B