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

Table of contents

Details

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.

Software

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.

I/O

LCD pin Name Description Centronics pin DB25 pin
1 Vss GND 19 → 30 18 → 25
2 Vcc 5V n/a n/a
3 VLc Contrast (10k trim-pot) 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 Ω to 5V) n/a n/a
16 VB- Backlight (GND) n/a n/a
Testing LCD on breadboard
Cutout for LCD
Cutouts for power jack and connector
Power jack and Centronics connector
LCD mounted
LCD mounted
Unit complete, showing MP3 information
Backside of complete unit
Inside complete unit

Screen shots

LCD Smartie, MP3 information
LCD Smartie, temperatures
LCD Smartie, light levels
LCD Smartie, voltages

Schematic drawing

Parallel port LCD schematics

Parts list

  • 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