Smart Alphanumeric Displays

Smart LED matrix displays are often used in medical equipment, printers and measurement devices. They look good in direct light conditions. Examples of such displays are the Agilent (formerly HP) HDSP-2xxx series or similar devices made by Siemens and others.

The HDSP devices require a parallel databus (8 bit), addressbus (6 bit) and some controlsignals (RD/, WR/, CE/, RESET/). I have used the mbed parallel bus expander described here ( to control the display through the mbed I2C bus. Here is the timing diagram for a write operation to the display.


The display driver software has been adapted and integrated using code from several sources. It provides basic initialisation and control methods as well as printf, cls and cursorcontrol functions. The examplecode should help you use these displays in your own applications.

This is what it looks like in a testcircuit.


The mbed and the bus expanders are shown in the picture below. Note the 3 PCF8574 devices on the right hand side next to the flatcable connector.


The code can be found here

1 comment on Smart Alphanumeric Displays:

28 Jul 2014

could you please tell me how to interface a seven segment to the board

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