LCD Display (Wiring)

    Around this time, my son broke our outdoor thermometer.  Instead of going to Canadian Tire or Home Depot and buying a new one, I had a Rube Goldberg moment.  I had the outside temperature, but the only way I had to display it was to view it on the server's display, which was not very convenient.  There is a surplus electronic's store on Queen Street west in Toronto called Active Surplus.  Active Surplus has all sorts of things you want, and a few that you don't.  One thing that they do have is a selection of surplus LCD displays. I picked up a 4 x 20 character LCD display for about $20.  These displays are based on the Hitachi 44780 controller which uses an 8 bit parallel interface.  This is a very well known standard, and is easy to program.

    I used the following wiring to connect the LCD display to the Parallel Port:

Wiring for LCD Display.  Click for larger image.

    In order to provide power, I used the +12v supply from the servers power supply.  I created a harness that plugs into one of the unused Molex Power connectors.  As the display uses about .08A with the display on full, I installed a .10A fuse into the harness.  I used a round connector (the type with the pin in the centre commonly found on walkmans, laptops, etc) and mounted it to a spare slot cover.  I made sure that the centre pin was positive, as I didn't want to blow the fuse by inserting the plug, and having it ground out to the slot cover.  The picture shown has 2 of these connectors.

Power Harness.  Click for larger image.

    I used a 2 pair 22AWG phone cable to run power from the server to the LCD display, as this was the cheapest cable available at Home Depot at the time of construction.  I doubled up the pairs to minimize voltage drop, and ran this to the LCD case.

    In the LCD Display's case (aka the wooden box), I installed a properly sized resistor to drop the voltage to 8v and limit the current for the LCD display.  A 7805 voltage regulator in a TO-220 package for the logic on the display.  No heat sink was required for the low power levels that are being used.

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