Parallel port IO module

This page is kept for historical interest. It may document projects or methods that are obsolete and/or no longer relevant. The information here is not kept up-to-date.

I'm not using this module anymore, there are much easier ways to interface inputs and outputs these days.

Parallel port IO 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 inputs. The parallel port is pretty easy to access in most programming languages. The module as 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 scripts, signals and alarms can be triggered. Making it possible to create a Linux server status panel (see images). By using 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.

Inputs

The parallel port has 5 status pins that can be used as inputs by pulling them low using 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 pin 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 a LED indicator.

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

Description	DB25 pin	Centronics pin
Strobe	1	1
Data bit 0	2	2
Data bit 1	3	3
Data bit 2	4	4
Data bit 3	5	5
Data bit 4	6	6
Data bit 5	7	7
Data bit 6	8	8
Data bit 7	9	9
Acknowledge	10	10
Busy	11	11
Paper out	12	12
Select	13	13
Autofeed	14
Error	15	32
Reset	16	31
Select	17	36
Signal ground	18	33
Signal ground	19	19 + 20
Signal ground	20	21 + 22
Signal ground	21	23 + 24
Signal ground	22	25 + 26
Signal ground	23	27
Signal ground	24	28 + 29
Signal ground	25	16 + 30
Shield	Cover	Cover + 17

Bash Scripts

Lifesignal

Done every 5. minute, using crontab, and sends a signal to a monitoring unit. One puls on 0.5 seconds is sent to binary address 8.

#!/bin/bash
/var/www/ctrl_files/set_port 1 8 0.5 0.5 > /dev/null

Reset_alarm

Sends lifesignal to a monitoring unit and closes additional alarm outputs.

#!/bin/bash
/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 "lifesignal sent to mmu"

Turn_port

Turns an output on or off.

#!/bin/bash
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.

#!/bin/bash
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.

#!/bin/bash
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'); }

Gallery

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  Parallel port

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  MJ-8050

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  Linux server status

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  Linux server status

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  Linux server status

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  MJ-8050 in the Rack box

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Software screenshots

• DVC
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• Hebo
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• Web
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  WAP control

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  Internet control

Schematic drawing