Knowledge Base

The HD8 has a built in operator interface (Man-Machine interface). The operator interface consists of:

3 push buttons

These are miniature momentary action push buttons, wired to dedicated inputs. They are sensed by a program just like any other input, though the SPLat programming language contains special instructions that are designed to simplify programming user interface operations. The buttons appear to your program on inputs 4, 5, and 6.

Numeric Display

The 3 digit numeric display uses 7-segment LED technology. Numerals are formed by selectively turning on the 7 segments. Each digit is driven by 8 dedicated outputs, the eighth being a decimal point that is located to the right of its associated digit. Thus the number range that can be displayed is 0.01 to 999.

In 7-segment displays the convention is to use letters to designate the segments, according to the following diagram:

The following table defines the output numbers used for the segments in each of the 3 display digits.

 LeftMiddleRight
a51321
b61422
c71523
d81624
e91725
f101826
g111927
dp122028
Example Code

There is a working example that includes some handy subroutines for displaying numbers on the 7 segment LEDs.

Open the HD8TemperatureExample.spt file in SPLat/PC.  If you have one of the TP11027 thermistors then you’ll see the temperature displayed in °C.

Faceplate and graphic overlay (you supply)

The HD8 is designed to be mounted behind a flat faceplate. The plate requires cutouts to match the buttons and digits. You will find dimensioned drawings in the files resources area of the resources CD or on our file resources FTP site. The board needs to be spaced off the faceplate so the tops of the push button switch stems fall minutely (<0.1mm) below the outside surface of the faceplate. You then place a flexible polyester or Lexan graphics overlay on the outside surface and the buttons can be activated by pressing them through the overlay. You can see more detail in the MMi202 documentation.

Warning: The board and the metal faceplate (or any other metallic surface that the board is mounted to) must be attached using metal screws and no insulating hardware so they are at the same potential. The mounting holes on the board are deliberately made with exposed metal. Failure to “bond” the face plate to the board will expose the board and the LCD to the risk of damage from static discharge.