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hansmw
Posts: 7
Supporter
In the first place: Happy New Year to all of you.

For my first Mobiflight project I need four 7 segment displays. After reading several posts in this forum I decided to buy three 8 digit MAX7219 pcb (green) from Ekstein Komponenten.
in Germany.

I will need 2x 3 digit and 2x 5 digit displays and I already understood that it should be Common Cathode versions. I plan to remove all the 4 digit blocks from the MAX7219 pcb's and manually attach the new displays to the pcb. I have 3 MAX7219 boards available.

I plan to attach the 3 segment displays to the first pcb and the 5 segment displays respectively to pcb 2 and 3. From the forum I understood that this should be possible.

My questions are:

1. Do 5 digit 7 segment Common Cathode displays exist?

2. How exactly do I connect 3 an 5 digit displays to the MAX7219 board? Is there any scheme available?

Thanks in advance for your help.

Hans
[Last edited by hansmw, 2021-01-03 08:11]
2021-01-02 09:53
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pizman82
Moderator
From: ETSI, Germany
Posts: 6007
Supporter
Servus Hans.

This is possible:

A example for a 5 Digit Display....
https://www.ebay.de/itm/0-36-inch-7-Segment-5-Digit-LED-Display-Digital-Common-Cathode-Blue-/353230778242

Whatever there exist lots of different Displays.... basic logic in most cases.... 7 Pins for Segments.... 1 Pin for DecimalPoint and 1 Cathode for each Diggit.
So 5 Diggit Display = 7+1+5= 13 Pins ( Maybe 14 Pins with 1 dead Pin ) 3 Digit Display = 7+1+3 = 11 ( Maybe 12 Pins also 1 Dead. Cause they build symetric)

***********
About Wire Logic.



The "empty" Max Tube after you remove the diggits have 24 Pins ( 12 each side)
These 12 Pins represent 7 Segments 1 DecimalPoint and 4 Cathodes .
The Segments and Decimalpoint is SHARED..... Means the Left and Right block use the same Signals.
If you use 1 Display on the Tube you can use whatever the left or right ports.
If you use 2 Displays you could combine them so you also use only one side..... But sure its more easy to wire one display to the left and the other to the right.
The CATHODES are not shared..... 4 Left and 4 Right... So one individual line for each of the 8 Diggits you can use.

What cathodes you use is your choice.... For example the 3 DIg Displays you share you can wire 123 567 or 234 678 .... ( 2 will be empty any way)
In theory you can also wire 123 456 .... But then you must wire from the second Display 1 Cathode line to the Left Block and the other 2 to the right block)

In the 5 Digit Display you MUST wire them into both sides.... The Segment and DP lines can be used from ONE side.... But in case that side only have 4 Cathodes you must use also the 5th cathode from the other block..... Here you normaly use 12345 or 45678 . In theroy also something like 34567 is possible but not make much sense.

***************
Last Note:
Get in contact to Stephan via DISCORD...... He write a nice guide ( pictures) when he wire his MCP.
Also interesting is HELIMECH (Karl) on Youtube. Check his MCP and PEDESTAL Videos. There he show the full logics in a realy perfect system.
https://www.youtube.com/channel/UCk3QdcLf2UPk0GCNj2JhmqA
Good Luck !
2021-01-03 15:43
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hansmw
Posts: 7
Supporter
What a reply #pizman82. I am impressed :thumbup:

You made me very happy with your great input. I have something to study on again.

Hans
2021-01-03 21:28
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RJPotts
Posts: 13
Supporter
Hi pizman82

Many thanks indeed for this!

I'm using those details to build some 5 & 6 digit 7-segment displays. I decided the easiest way to do so was to buy some round-pin PCB IC mounts and create a loom as an adaptor between the previous display mount and the displays themselves.

Soldering into the female end of the pins was ok but soldering the male side even as quickly as possible (well as quickly as my dodgy eyesight and shaking fingers allows haha) distorts the plastic round the pins. That's why one end is straight to individual pins, which is how I'll do the remaining sections (4 x 6 pins per 5 or 6 segment display). It'll mean that the order of the wires only needs to be considered when assembling, rather than whilst soldering.



PS, I did donate but it doesnt show up in here, maybe because I did so direct from the software, not from here.
2021-05-03 20:09
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RJPotts
Posts: 13
Supporter
6 digit example, 5 digit would be almost the same, just with one fewer wires;

[Last edited by RJPotts, 2021-05-07 19:49]
2021-05-07 19:39
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pizman82
Moderator
From: ETSI, Germany
Posts: 6007
Supporter
Hi

Some days ago we startup to make some experiments with KiCad https://www.youtube.com/watch?v=-_nZZLuwYd0

May you should check our Discord Groups.... We have high advanced PCB Builders there.

Sure... Solder Wires and build connectors with Pin rows work.... We all do this for years....
But maybe you like to go a step more professional....
Check this out !
Good Luck !
2021-05-08 21:31
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RJPotts
Posts: 13
Supporter
Hi,

I'll check that link / software out, thanks.

I am looking for a simpler way of doing things, a rough guesstimate suggests 174 wires needed (& 2 ends each of course). I've tried taking the metal part out of a dupont connector and crimping it a bit tighter, that would work for the connection to the display modules but the pin on a dupont connector is thicker than the IC mounts so still needs soldering at that end.

Certainly a customised PCB would look a great deal better than the forest of wires! Will judge the amount of work involved. I have got a mini cnc router, havent tried engraving PCB with it yet but there's a first time for everything! :D

Because of the low price of arduino mega clones I'm thinking that I'll create a mount under each radio panel, to hold a mega & the 7219 PCB (or customised PCB of course), get each working well and keep them as standalone panels with the only connection being a USB plug.

Best regards
Richard
2021-05-09 17:08
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pizman82
Moderator
From: ETSI, Germany
Posts: 6007
Supporter
We not have expereince with CNC and producing PCB´s......
We just check the "lazy" way..... And google for a shop.

For example..... Stephan designed a 2 Layer PCB as a Mega2560 shield..... Customized to his panel ( a Hispapanel FMC CDU) ..... This ends in acouple of 10x2 and 20x2 Flat wire conectors....
So he build a PCB with also Connectors so the full Setup is just connceted via 4 single Flat cables..... No single wires.... no solder work.



Costs.... As he said roundabout 20-25$ for 5 PCB´s and the needed Connectors and Pin headers..... With shipping maybe finaly 30$ if you order 5 PCb´s .... Means 6$ for one.

Way cheaper as the premade Stuff in the Cockpitbuilder Shops !
Good Luck !
2021-05-09 19:59
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RJPotts
Posts: 13
Supporter
Interesting, more ideas to try! I hadn't thought of using ribbon cables to connect components but it certainly makes sense.

Presume you found a pcb shop that was able to use a file from KiCad? Local or overseas?

Best regards
Richard
2021-05-09 21:42
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pizman82
Moderator
From: ETSI, Germany
Posts: 6007
Supporter
Stephan need to awnser..... But pretty sure Overseas....

BUT

Whats the problem you think about ?
If i understand the Guides ( and what stephan told me) correctly then KiCad support a standard File Format that is used and compatible with other Design Tools and sure compatible with PCB Manifactures isn´t it ?
Good Luck !
2021-05-10 19:31
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patEGWU
From: Northolt, United Kingdom
Posts: 9
They are gerber files. Kicad can generate them. I used kicad and then the famous chinese manufacturer (I paid less than £10 for 10 PCBs) to make a module that uses two Max chips and that you can connect 3,4 or 5 digit displays without changing anything or soldering any more wires and chain very easily. Plan to update my radio stack using 5 of them.
2021-05-12 00:47
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StephanHo
Moderator
From: EDDG, Germany
Posts: 1857
Supporter
Hi together,

the company in china who produces cheap pcb's is

https://jlcpcb.com/
Grüße,
Stephan (Time: UTC+2)
2021-05-12 19:55
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steffen
Posts: 28
Hello, I had already ordered some but had to find out that the quality is not as I wanted it to be. With the displays, it seems to me that there is a short circuit somewhere, just to find out what I don't know. Now I'm looking for someone to check the circuit board for me, I'm curious.
2021-05-24 11:42
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pizman82
Moderator
From: ETSI, Germany
Posts: 6007
Supporter
Hi Steffen.
Do you got a Multimeter ?
If Yes.... Testing the Board is no big deal.... All you need is the diagramm ( That you design) to know what line should be connected to what point.
Then you can check it yourself.

Whatever i´m wondering. If one board is broke i would say it´s a quality issue.... But if all got a issue then it sounds you make a wrong design maybe.

If you like i can support you via shared screen and a Webcam.
Good Luck !
2021-05-24 13:02
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kjoussen
From: Hamburg, Germany
Posts: 171
Hi Steffen,

as i already mentioned here https://www.mobiflight.com/forum/topic/6607.html i found tailors on Ali who are selling 1 to 5 and even 6 digit displays for very low prices.

I think 7 digit is not existing.

But as these are having a small "border" you should be able to combine a 3 digit and a 4 digit without noticing.

1 to 5 digits: https://de.aliexpress.com/item/32932664728.html
6 digits: https://de.aliexpress.com/item/1326420858.html

Cheers

Kai
2021-11-01 22:28
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