Help please - Can I build a 5x7 segment display?

Other Hardware LEDs and Multiplexing
1

Hello reader

I'm looking to build a Master Control Panel (MCP) for my 737 home cockpit project using an Arduino Mega interfaced with Prepar3d and the exciting Outerra environment.

I know this is a popular project here at the forum, but I can find no real solutions.

I have a replica front panel and am trying to incorporate a number of 0.36 - 7 segment arrays.

From L-R the unit requires 3, 4, 3, 5, 5, and finally 3 arrays. Each has its own rotary encoder, and each has individual limits. e.g. Course/Heading=360 degrees, Altitude limit 45000, V/S=Say 5000 and Airspeed= Say 500 max. This 4 array is a little different as its 1st led lights 3 options like an annunciator, for Mach speeds, but I think I can achieve this with an overlay and lighting just the a,d and g segments.

Researching many sites online has been much help.

It may be overkill but I am considering 6 individual Max7219 backpack modules simply for ease.
These boards generally come c/w 2x4 digit cathode modules attached but can be bought cheaply on Ebuygum for as little as £1.25 each. There may also be just a 4 array backpack too.
Is it possible for me to cut away 1 of the 4 pack components and solder 1 display in its place to produce the 5 way displays? Obviously this is needed to fit into the cutout in the fascia panel.

Would this require major re-code in the sketch?

Any help or advise would be much appreciated by this newbie.

Cheers
Kev

2

You can buy MAX7219 modules that have just 5 digits. This would be easier than trying to cut down/modify a 4/8 digit version.

3

Actually, I get the impression that he wanted to match a peculiar cut-out in a front panel. The module you cite uses separate digits - if there was one with eight digits using separate displays, he could de-solder the ones where they were not wanted.

To me, the obvious approach is not to have them project through the panel - just mount an eight digit module behind the panel and whatever digits are obscured are not used.

4

Thanks both for your suggestions/advise.

I have searched quite hard for 7219's with differing digits. I'm looking for 0.36 size, which is quite elusive in anything other than 4. Cathode preferably too.

Paul, yes at the price I'm thinking the same way, although flush fit would be very much more appealing.

I wondered if a trio offered for a voltmeter might be adapted in some way.

This is the type of thing I need to achieve.

5

Have you looked here? Many sizes, mounting types, many colors, and common cathode for use with MAX7219
http://www.kingbright.com/
Can order direct from them, or just find a part number and order from a distributor like www.digikey.com

6

CrossRoads, again thank you for your response.

I must be having brain fade. I know kingbright are a prolific builder of 7-segment units, but I can't find any on that site at 0.36"

The 3 digit packs are 0.4, 2's are .39 or .4 aargh

As I said at the start, I'm finding it tricky, hence the need to modify an easily sourced part to satisfy the requirement.

Perhaps you may know of a pcb module or circuit which I could build from scratch which would allow me to daisy chain these 6 individual arrays?

Many thanks for suggestions so far.

7

For such a specific requirement maybe the only way is to mount 5x single digit modules like these on to stripboard and hand wire the pins to suit MAX7219 requirements.
Or get someone to design a custom PCB for you that you can get made by Oshpark, Seeed or one of the other PCB services out there.

8

Riva:
For such a specific requirement maybe the only way is to mount 5x single digit modules

Well, other options would be 1x four-digit module + 1x single-digit module or 1x two-digit module + 1x 3-digit module. Would make wiring slightly easier than 5x single-digit modules.

In fact, you could make all your required displays with a total of 5x three-digit modules + 4x two-digit modules, which keeps the number of different components down and the amount of wiring down.