LCD unit driven by a computer parallel port

From CaveLab
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 connect an LCD these days.
PLD on top of the TV

Very simple LCD unit with almost no external components, driven directly by a computer printer port.


This very simple module is driven purely by a computer parallel (printer) port. Almost no external components are needed; a few capacitors for voltage stabilization, a trimmer for the contrast adjustment and a resistor for the LED back-light. All communication is done directly over the parallel port data lines. The LCD is powered by an external 5 V power supply. It can't be placed too far from the computer though since the recommended max length of a parallel cable is 15 ft.


I used LCD Smartie to drive and control the display. Things like MP3 song information, system temperatures etc. are available right out of the box. And they have a number of plugins available. If you want to show some custom data you can write it to text files and have LCD Smartie read and display the content of those files. It's even able to cycle though a list of screens to show multiple pages of information, very cool.


LCD pin Name Description Centronics pin DB25 pin
1 Vss GND 19 Arrow right.png 30 18 Arrow right.png 25
2 Vcc 5V n/a n/a
3 VLc Contrast (to a 10k variable resistor) n/a n/a
4 RS Register Select 31 16
5 R/W Read/Write (to GND) n/a n/a
6 E Enable 1 1
7 D0 Data 2 2
8 D1 Data 3 3
9 D2 Data 4 4
10 D3 Data 5 5
11 D4 Data 6 6
12 D5 Data 7 7
13 D6 Data 8 8
14 D7 Data 9 9
15 VB+ Backlight (120 ohm to 5V) n/a n/a
16 VB- Backlight (to GND) n/a n/a


Screen shots

Schematic drawing


Parts list

Qty. Part
1 × Capacitor, aluminium electrolytic, 10 µF, 25V
1 × Capacitor, aluminium electrolytic, 47 µF, 25V
1 × Capacitor, ceramic, 1 nF, 100V
1 × Capacitor, metallized polyester foil, 10 nF, (0.01 µF)
1 × Centronics, chassi, 36-pin
1 × Enclosure, plastic (Alu. lid), 110x70x49mm
1 × Fuse 5x20 mm, 200 mA, fast-acting
1 × Fuse holder, open, PCB, 5x20mm
1 × Fuse holder, open, PCB, Protective cover
1 × LCD display, dot matrix, 16x2, LED green
32 cm2 PCB, stripboard, 100x160mm, 160cm2
1 × Power jack, panel, 2.1mm, plastic housing
1 × Resistor, carbon film, 0.25W, 120 Ω, 5%
9 × Spacer, round unthreaded, 3mm, Ø6mm, Delrin
16 × Straight pin header, female, Single row, 2.54mm
16 × Straight pin header, male, Single row, 2.54mm
1 × Trimmer, carbon, 10 kΩ, horizontal