The designation “HDSP-2000” refers to different variants of LED matrix displays that were developed by Hewlett Hackard and later also offered in a variant by Siemens. What they all have in common is that they display four characters with a matrix of 5×7 characters each with a height of 3.7 mm and use a DIL-12 housing. Multiple displays can also be placed side by side to form longer lines of text.
The first displays with red LEDs were used in devices such as the HP 9825A in 1976. Later there were also other variants with yellow and green LEDs. A special feature is the elaborate construction with ceramic carrier and glass cover, which was colored in the red version to achieve a higher contrast.
AlphaClock is the sort form of “alphanumeric clock” as the displays used can also show text. The following video was done with the first version of the firmware.
A while ago I started to deal with the topic “micro controllers”. The first trials were with an Arduino micro which I also used to test old LED displays like the HDSP-2116 or DL-2416.
One advantage of the Arduino Micro ist that it can be plugged in directly to a breadboard and has a micro USB connector for data transfer and power supply. However from LCD2USB I also know the ATmega in a DIP package. For normal operation with external clock this controller only needs a crystal and two capacitors.
My idea was to combine an ATmega328P with two DL-2416 from 1987 and a DS3231 realtime clock module. The whole thing was also a project to learn to know the development environment as Visual Studio Code and PlatformIO as well as the way how the microcontroller works in terms of interrupt control and PWM.
The Siemens DL-2416T, which was also manufactured by HP as HPDL-2416, is a four-digit LED display with an integrated driver for displaying numbers or text. The display is made with 16-segment LED displays with one decimal point each. Although the technology dates from the 1980s, these modules are still available from some dealers as new old stock with a production date from the late 1990s. The pin-compatible module HDLO-2416 by Broadcom can be used as a direct replacement and uses a 5×7 matrix and offers an extended character set in which the codes 0-31 are also assigned to national special characters and symbols.
Around 2013 I bought several used Avago HDSP-2112 display modules. However, it took until 2021 until I implemented a prototype with an old Raspberry Pi.
The special thing about these modules is the technology: the modules are suitable for a DIL-28 socket with a pitch of 2.54 mm and contain eight characters with a matrix of 5×7 LEDs each, which is only about 5 mm high. Several modules can also be mounted next to each other in order to build longer lines of text. In addition to this model, there are also other colors:
HDSP-2112: red (high efficiency)
The series HDSP-250x provide a bit larger characters with a height of about 7 mm. Besides the different dimension those modules are otherwise pin compatible and functionally identical. Besides that there is also a variant HDSP-253x which has a slightly more compact packaging and a similar pinout fitting a smaller DIL-30 footprint. However the control of the HDSP-253x is identical to the other models.