Introduction: HDSP 2000 Display Controller Board
The clock picture demonstrates a typical example of how such boards may be used. The six pack was for my friend.
The board will provide the circuitry for two, four character HDSP-2000 displays. The communication to the display driver boards will be in the form of RS232.
Only eight characters are visible per data packet.
I designed this project for a friend who had a number of HDSP displays in his workshop. I also had a few of my own. The task was to design a simple interface board which performed all the required control signals for the displays and interface via a simple RS232 connection.
I've attached the following;
1. Schematic Diagram
2. Board General Arrangement Drawing
3. PIC18F14k22 HEX file (the file to upload to the PIC to run the firmware)
4. Gerber Files
5. Project Documentation
How the Circuit Works
The driver IC performs three key functions.
The first is the strobing of of the HDSP-2000 columns. This is achieved by use of five PNP LED driver transistors. The strobing rate is approximately 500 Hz, 100 Hz per dot matrix column. One column of each character matrix is displayed at a time. For example, if column driver zero is active the first column on all eight character matrixes is active.
The second function, which occurs between each column change is a 56 bit serial data stream which is sent to the HDSP-2000 shift registers. This reloads the new column dot matrix information. All columns are switched off during the shift register updates. Due to the ‘daisy chain’ connection between the two HDSP-2000 displays this represents 28 bits per display.
The third function is to check the received RS232 data for a genuine packet of data. If the carriage return is present on byte 9 then the data is cleared for translation. Translation cross references the received ASCII codes to characters. The character dot matirx data is in turn looked up from the onboard ASCII dot matrix data array and arranged for transmission for the HDSP-2000 display.
How to use
The display driver controls the HDSP-2000 displays to display upto eight characters. The characters to display are sent to the driver IC via RS232. The RS232 must contain the following sequence of bytes.
1: Character 1 (Left most character on the display)
2: Character 2
3: Character 3
4: Character 4
5: Character 5
6: Character 6
7: Character 7
8: Character 8 (Right most character on the display)
9: Carriage Return (ASCII = 13)
It paramount that data transfer is not disturbed as there is no start of packet syncronisation byte. A short delay of several milliseconds must be present post display power up before sending the first data packet. This ensures syncronisation.
The BAUD rate is 1200 bits per second. No others are supported.
Source code is included within the Project Documentation PDF, it is written using MikroBasic.
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