How to connect a MCP panel to the IOCards (English).

J. Pedro Bibiloni. Translation by Manolo Hdez-PeñaLopez Muñoz

Once the MCP is already done (take a look to my tutorial about it) let's connect it to the IOCards (Master and display cards). Though this is really easy, I'm going to explain how I did it just in case this tutorial makes it easier to you. As always, I've been taught by Manuel Vélez, the IOCards designer, who in addition gave me the idea of doing it this way. Thank you Manuel.

Doing it the way you're going to learn here is with the only aim of building the parts in a modular way. This way, disconnecting the MCP from the IOCards will be really easy.

Let's start by connecting the displays to the corresponding Displays card. Instead of directly welding the displays pins to the card pins, we are going to build an intermediate card where we'll install some 40 pins connectors. This way, we'll distribute all the displays in several connectors.

My MCP has 19 displays. 14 are connected to the displays card and the rest to the Master card. Later I'll explain how. The ones to be connected to the Displays card are drawn in green. The ones in red are the fixed zeroes for the altitude and vertical speed (due to these displays have only two states -zero or off- they will be connected to the Master card outputs). In addition, the minus sign for the vertical speed has only to states so it'll be connected to another Master card output. This way we save 4 connectors in the displays card, so one card is enough to manage all the MCP displays.

The 14 displays that I'm connecting to the displays card are as follows:

Course: 3 displays

Ias/Mach: 3 displays

Heading: 3 displays

Altitude: 3 first displays

V/S: 2 displays (second and third displays)

We start by placing three 40 pins connectors on a standard circuit card.

Once the card is cut to the desired size, we must cut the tracks as shown in the picture. We can use a Dremmel tool or just a cutter.

Once we've welded the connector pins we have to weld each display pin to the corresponding connector pin. I recommend drawing a previous scheme based on the displays technical information. I've used Kingbright SC52-11HWA displays and the scheme is the one showed in the left. It's better testing the first display you weld prior to continue welding without testing.

This is how it looks when we've finished this first step.

To make things easier, I've used some 40 threads flat cable as the ones used for hard discs, grouping cables for several displays.

And this is the final result: from the MCP panel to the intermediate card, and from this to the displays card.

As I've said before, displays with only two states (zero and off) are directly connected to the Master card outputs. We'll connect in parallel all the segments that forms the zero (each one with its 470 ohm resistance) so we'll have only one cable to connect to the Master card output and other to the common ground (see picture on the right). I've used one output per display so the brightness is the same as the displays connected to the Displays card. Later, we will program how to manage the displays connected to the Master card.

Now, we are going to use a new intermediate standard card with two connectors: one 40 pin for inputs (push buttons...) and one 20 pins for outputs (two states displays, minus sign, decimal points and individual leds).

In the picture, you can see already welded, all the resistances for the outputs, except the ones for the individual leds, which I've decided to install directly on the MCP panel.

In this picture you can see all the cables already welded. The ones on the right are for the two states displays and the ones on the left are for the individual leds.

This picture shows how this new intermediate card are connected to the Master card outputs through a 40 threads flat cable. This cable is also divided into two 20 threads groups: one for the MCP outputs and another for my future EFIS panel outputs.

Now we have to connect the inputs. Thanks to Baltasar Rodríguez (Tasin) who let me use this picture. It defines clearly each pin on the Master card. Remember that we have four 9 inputs groups in each connector and one ground for each group. Also remember that one rotary switch needs three consecutive inputs in the same group.


We can start welding the inputs cables, not mixing one group ground with another group input.

This picture shows all the outputs (20 pins connector) and inputs (40 pin connector).

Both intermediate cards finished and ready to test.

Connect the MCP to the IOCards through the connectors. Start the controller software and we can test if all work properly (leds lights on and inputs are received by the software). Take note in order to identify each display, input and output. We'll need this information to program the MCP operation.

Finally, once all have been tested it's time to close the MCP box. First we can fix the intermediate cards to the back side of the box.

A close picture showing the inputs and outputs connectors card and the displays intermediate card.

I've installed the IOCards inside an old Olivetti PC box.

We can take all the components out of the box, except the power supply which we can use to power the IOCards. In my case, the source was really unstable, so I took it out too.

I've used the floppy disk B power supply connector from another PC, testing that 5 VDC were available with the black and red cables.

Finally, all cards are installed inside boxes. Please take into account that electronic cards must be far away from metallic parts (box sides) to avoid short circuits problems that could damage the cards.

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