General IO Panel Cards

General IO Panel Cards

Some panels, especially in the Overhead, will cost too much effort or are not worth while making special Panel Units for them. Also the front panel(s), you might already have, are easier to fit using some general IO cards, where you can connect necessary parts: switches, rotary switches and rotary encoders too. You also need some LED indicators but less 7 segment displays.

This is why we developed 2 General IO cards.

  1. General IO (input/output) card with 2 MAX7219 chips and 4 74LS165 chips. This card allows to connect 32 inputs and 128 LED’s (or 16 7-segment displays).
  2. General INPUT card, having 8 74LS165 chips thus allowing 72 inputs.

Of course cards can be linked into a FSIO chain.

If you understand the concept of panel units, you will not have trouble to understand these cards.

General Input Output Card

The layout of the General IO PCB was setup to allow home-made double sided cards with the assumption that you cannot make plated through holes or via’s. So all soldering of connectors can be done from one side. This design was not easy, as the card has many connectors, so I had to allow a lot of via’s that you will have to hand solder (little piece of wire soldered on two sides connecting Top and Bottom PCB layers). It should be “do-able”, but not so easy, I must admit.

As many things I present on this site, Sebastian not only assisted, checked and re-checked, but also had the PCB professionally produced. It came out great, as you can see on the picture below.

Each input connector carries 8 inputs + GND, so with one ribbon cable you connect 8 switches/pushbuttons or rotary encoders etc.


We have foreseen 16 output connectors. Each connector carries 8 segments + one common anode to connect 8 LED’s. If you need the card for 7 segment displays, you do not need to solder all the output connectors as the common anode signals are available on another single row connector.

General INPUT card

The schematic should not come as a surprise. The card has just 9 74LS165 chips. Each connector caries 8 inputs and one GND signal. Same as above.

The PCB was designed SINGLE sided to allow home builders to make the cards. You can see that you will need some top wires but I think that is absolutely do-able. Sebastian home made this card shown on a picture below.


You can chain-connect FSIO cards up to a total of 32 input chips, e.g.: 1 x General IOcard and 4 x General Input cards. For a full blown overhead I think you will need that for sure.

You will find the Eagle Files in the downloads for the hardware.


There is my testbed on the picture below. I am using 2 CPU cards, 1 EFIS, 1 MCP, 1 General IO and 1 General Input cards here.

Top left (little white table board) you will see the EFIS and MCP chain-linked to it. The CPU(1) driving these is not visible on this picture.
     CPU(1)     <— chain link —>     EFIS     <— chain link —>     MCP

Lower part of the picture, on the brown board you will see (from the left): the CPU card that is connected to a General IO card and chain-linked General Input card.
     CPU(2)     <— chain link —>     General IO     <— chain link —>     General Input

CPU(2) drives 13 input chips (of 32 possible) and 2 output chips (of 8 possible).

The Flaps gauge is connected to one of 6 servo ports of the CPU(2).

The green thin part, left from the middle is a mini Gear lever. The LED on the experimental board are 2 * 3 gear lights.




PCB’s for this unit are available My First Boeing shop