Projects
The Two Line Mini-Terminal is a embedded microcontroller board designed to implement a limited but low cost terminal. The board was designed to be the same size as a 2 line by 40 character LCD such as the OPTREX DMC 40218. With mounting holes in the same pattern as the LCD the controller board can be piggy backed with the display. As an input device the terminal uses standard IBM compatible PC keyboard. In a normal full duplex mode the controller converts the keyboard scan codes to ASCII and transmits them to the RS-232 output. Input from the RS-232 is displayed on the LCD. The software does vertical and horizontal scrolling of the incoming characters.
To view a PDF version of the manual click
here (140 K; July 97 version).
Download the code. Ordering information.
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Please be patient while the LEDSign loads...
This is just a Java app but check out a real LED Dot Matrix display project.
It's difficult to get a good
photograph of LEDs.
The display is much brighter then it appears in this photo.
| The board is driven by a Maxim MAX7219 which
has a serial interface; it can be controlled by a any
microcomputer with a SPI or three output lines. The board
is 2.75 inches by 6.5 inches in size;
mounting four .8 inch LED displays and two .56
inch displays as well as six individual LEDs, a 7805, the
MAX7219, and a five pin header. A LED display circuit is straightforward but wirewrapping one is a long tedious job; save time and effort by ordering a printed circuit board.
Randy
has some C code for the chip on his site. I am currently running the clock with a MC68HC811E2 using a software clock. It features an alarm with snooze, beep on quarter hour, dim at night and a TALKER so that I can communicate with it using PCBUG. Download the source code. |
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| If you want to interface a LCD to your
project but are short the number of I/O pins required,
you could use the Motorola SPI and an inexpensive 74HC595
shift register. A printed circuit board with the IC, a
SIP connector, space for a dropping resistor if the LCD
has a LED backlight and an optional pot to adjust
contrast is less than 1 x 2 inches in size. In the photo
top left the contrast input was hardwired to GND. In the photos in the
lower row trim pot as well as the power for the LED backlight is
installed. The LCD is
interfaced in the 4-bit mode with first four bits of the
HC595 connected to DB4-7 of the LCD and RS & E
connected to output bits 4 & 5. All you need it make
this work is a suitable subroutine. Download code examples for the 68HC11 and 68HC12. Here's the schematic . |
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Most LCD's are interfaced via a 16 position header located along the top or bottom edge. My pcb is designed to connect to such LCD's. However, some LCD's use a 8x2 position header along the side. I recently came across a board by Oleg Mazurov posted on BatchPCB for a SPI to a 8x2 type LCD. You can buy one directly from them.
If a SPI interface doesn't work for you then consider a IIC interface.
Roger's Embedded Microcontrollers Home Page 
This page written by Roger Schaefer. Last updated November
7, 2011
The LED Sign Java applet is
written and Copyright 1995 by Darrick Brown.