The electric circuit

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30. October 2014 by Peter

A few of you have asked me if I could show how I made the Electrical Display.

I would love to show a picture of how I have done. However the circuit board connects somewhat 78 wires. And I do like you guys, but not so much that I will disconnect 78 wires to take a picture. ūüôā

I have used Open Cockpits Display cards. If you use another card the wiring might be different.

A few basic things:

  • I use 3-digit units of the 7-segment displays. Green colour, 0.36 inches, common cathode.
  • There are 8 wires that are common by all displays connected to the same DisplayCard. However only 7 wires are used (The decimal is not supported by the OpenCockpits DisplayCard).
  • The 5 display units all have the same wiring (No matter if they shall display 2 or 3 digits). All have 3 wires, one for each digit. In this posting called A, B & C
  • I use a strip board. The strips allows several wires to be connected. If a section must be isolated the strips are cut.
  • I also use 20cm ribbon-wire with dupont-connectors. They are very easy to use and there are 10 different coloured wires.

In case you are unsure about the¬†wiring of the 7-segment display try this approach: On the DissplayCard take a wire from the shared group and a wire from one of the 16 pins. In the SIOC monitor set the card to “ALL ON”. Now connect the one of the¬†wires to any pin¬†on the 7-segment display. Then one-by-one connect the other wire to all the pins. In case nothing lights up then move the first wire¬†on to the next pin. At some point something will light up. Now mark what pin that connects to what. I normally start at the top as number 1 and number the rest of the pins depending of what segment that lights up ¬†clockwise numbering. Then attach the wires with the black at number 1, the white at number 2 and so forth. The last 3 (Orange, red, brown) is for the 3 digits A, B & C.

Using one OpenCockpits DisplayCard

Using one OpenCockpits DisplayCard

This is how you should/can do it.
On the strip board you add 8 pins 6 times in a row. This is for the shared pins.

In another row you add 2×3 pins a total of 5 times.¬† This is for each digit. NOTICE: The strips are cut! So there is no¬†electrical¬†connection between two groups.

The picture on the right shows how to wire the displays.

The 7 shared wires are connected to one part of the board. The last of the 8 wires that not are connected is the decimal point.

Beacuse I use a strip board and solder pins on the the board I just need to attach the dupont wires. All wires are connected so the signal delivered to via the yellow wire will be shared with all yellow wires. As you can see from the drawing the wires are connected from black to yellow.

The 2 or 3 wires for each segments/digits are connected to the board in different rows (Lower part of the strip board). If you look careful on the drawing you can see the the strips are cut between the groups.

So the first 3 wires only passes on the signal on to that unit of 3 digits and so forth. The only function of these groups is to pass on the signal. Because I use 20cm wires from the display units, I need to connect them to the board and then use another set of wires to connect to the board.

And so, this is how I did it.

In order to save a bit of money I only use two DisplayCards on my overhead.

One display card handles the IRS-display, that (In my overhead) has a total of 11 digits. This gives 5 available digits for the Electrical display (One 3-digit unit and one 2-digit unit).

The second DisplayCard is used for the altitude displays. As I have 5 digits connected to the IRS-display I need 7 digits on the second DisplayCard. Now here is a small conflict as 10 digits all ready is used by the 2 altitude displays. In order to squeeze it on to the second DisplayCard I only use 4 digits for the Landing display. I will never need to land above 10.000ft. So 9 digits for the landings displays and that leaves 7 free pins that can be used by the electrical display.

ElecDisplay2My wiring is shown here to the right.

Note the red arrow on top of the strip board. Because I have two DisplayCards in use I need to isolate the shared wires between the two cards. So I have made a cut down through the stripboard. So “group 1” gets common connections from one card, and group 2 from another card.¬†And no¬†signals are not mixed up.


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About BuildaBoeing

My name is Peter and I live in Denmark.
I am building the cockpit of a Boeing 737 in my basement using my limited skills and inspiration from fellow builders.
I post my progress on this blog and hope it can be an inspiration to others.

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