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Thanks for your tips thatchi,

I'm pretty familiar with the basics, but my problem is identifying what to do to modify the SISMO PCB, which uses one ground for all 8 segments.

Stephan - re-reading your explanation I gather I need to identify these microscopic ground connections for each of the segments on the PCB, and then find a way to cut them without damaging any others. It's a two-sided PCB to make things even more interesting.

Is there no other way? I wonder how the SISMO interface board works with a single ground line to all digits.

I'm not convinced I can get much further with this.

Paul

Hi Paul,

Since only one side of the board is shown by SISMO, I can only guess the following:

So you have to describe how the connection from this motherboard to the displays is made.
Can you possibly take pictures and upload them?

Are the displays also on a separate board or is there a plug?

Just make this connection and follow the traces from the P1-DISP connector.

Pins 1 and 21 respectively go to segments A, 2 and 22 at B, 3 and 23 at C .... and 8 and 28 at DP.
9/29 is not connected. and 10 and 30 is the GND that goes to all digits.

This pin 10/30 you have to disconnect once on the connector. Either on the motherboard, directly on the socket or on the counterpart, which is plugged into the main plug.

Thus, the display unit is initially separated from the GND.
Now it depends on whether the display unit is on a board or connected to a plug / cable.
If it is a board, you are looking for the pins / lines (starting from 10/30) that go to the 1st segment of the display unit. Once you have located this spot, you are following the link to the next segment. Once you've identified that, you're breaking that link from digit 1 to digit 2.
For testing, you can also put the 1st digit on GND and apply the + 5V with a resistor (470 ohms) to any segment. It should light up and only the segment you put on GND.
As long as you use a resistor for testing, you can connect the digits wrong, it can not break anything. You may even need to swap if your digits have a common anode.
So you work now digit by digit and test it through.
The decisive factor is that the connection to the GND and the individual segments is interrupted. If you have performed the separation, only 1 (!) Segment should light up.

Do not worry that the chip is broken. The chip itself is so sensitive that malfunctions often occur, especially with "flying wires". It makes sense then to have a board that I had linked. Soldered connections are always safer than stuck.

It is also important that the data for the displays no longer come from the SISMO module, but directly from the MAX chip. Accordingly, you should plan your wiring.

Hi Stephan,

I'll take a look at this in detail.

The displays are similar to this:

https://www.diytrade.com/china/pd/9088444/5_Digit_7_Segment_LED_Display.html#normal_img

They attach to a socket soldered onto the board and can be removed easily.

The PCB itself uses very small tracks, sealed well under a layer of conformal coating.

Paul

Hi Stephan,

I took a close look at this, and think the task is too difficult. The tracks are either very close to needed ones, or hidden (sorry I couldn't attach a photo easily to this reply).

I will try to return the module.

Thanks for all of your help, but I believe it is just as easy to build the module from scratch using Max7219 mounted displays.

Paul

Hey guys.

Are you sure this all is correct ?

I not have a sismo module to recheck this myself ( must see it with own eyes or i need a shematic plan of the PCB )

BUT
How does it work when you use the original sismo controller card ? . The Displays are Common Ground basicly.
Also there are shared Segment (+) lines for each of the 2 Digit Blocks.

That sounds to me like they work also with TWO Controllers basicly.... One for each 1x5 Display.
Now the question.... HOW should this work if all Ground are shared together and if Segment Lines are combined ?
If the grounds are realy shared display to display then also with original system all Displays will show same Data same time.
tzhere MUST be a seperation already.... Elseway this can´t work whatever you use the original Sismo Controllers.

Do you already try what i say above ?
So NOT use the official GRD Pins and use the Display Pins as GRD for D1, D2 D3 D4 and D5 .

I have also been wondering - how do SISMO get this to work with their boards? Perhaps a different way of controlling displays? Stephan might know the answer.

Took a look at sismo nav module. It looks like it only consists of 7segment led, button and encoder wired to back of panel . It does not have controller circuit. The connector at back , one for dual encoder, and one for 2x 5 digit led. And the pinouts of P1 as follows,
1 2
3 4
5 6
7 8
9 10
11 12
13 14
15 16
17 18
19 20
21 22
23 24
25 26
27 28
29 30
31 32
33 34
35 36
37 38
39 40

2 Display 7S - Segment B - For All Displays (CC)
4 Display 7S - Segment D - For All Displays (CC)
6 Display 7S - Segment F - For All Displays (CC)
8 Display 7S - DP - For All Displays (CC)
10 Common GND - GND for pins 1 to 8
12 Display2 - NAV Active 2
14 Display4 - NAV Active 4
16 Not used
18 Not used
20 Common GND - GND for displays 1 to 8
22 Display 7S - Segment B - For All Displays (CC)
24 Display 7S - Segment D - For All Displays (CC)
26 Display 7S - Segment F - For All Displays (CC)
28 Display 7S - DP - For All Displays (CC)
30 Common GND - GND for pins 9 to 16
32 Display10 - NAV Standby 2
34 Display12 - NAV Standby 4
36 Not used
38 Not used
40 Common GND - GND for pins 9 to 16

1 Display 7S - Segment A - For All Displays (CC)
3 Display 7S - Segment C - For All Displays (CC)
5 Display 7S - Segment E - For All Displays (CC)
7 Display 7S - Segment G - For All Displays (CC)
9 Not used
11 Display1 - NAV Active 1 (right display)
13 Display3 - NAV Active 3
15 Display5 - NAV Active 5 (left display)
17 Not used
19 Not used
21 Display 7S - Segment A - For All Displays (CC)
23 Display 7S - Segment C - For All Displays (CC)
25 Display 7S - Segment E - For All Displays (CC)
27 Display 7S - Segment G - For All Displays (CC)
29 Not used
31 Display9 - NAV Standby 1 (right display)
33 Display11 - NAV Standby 3
35 Display13 - NAV Standby 5 (left display)
37 Not used
39 Not used

P4 for 12v backlight

for dual encoder inputs P2
1 2
3 4
5 6
7 8
9 10

1 set A bottom knob
2 set B bottom knob
3 set A upper knob
4 set B upper knob
5 push button TFR
6 push button TEST
7 not used
8 not used
9 not used
10 GND
So for left 5 digit led, connect 1,2,3,4,5,6,7,8 to segment A,B,C,D,E,F,G,dot of 1st max7219 socket, and 11,12,13,14,15 to 1st,2nd,3rd,4th,5th digit pins of 1st max7219 socket ( you have 8 digit pins to choose, for example digit 1,2,3,4,5 or 3,4,5,6,7 or 4,5,6,7,8 ). similar connections for right 5 digit led.
for input, connect pins of dual encoder and x2 buttons of your choice to mega2560 pins. then you ready to test.
i dont have sismo to test for you. so maybe pizman or stephan can comment on this.
honestly , i think it lots cheaper to get 2x max7219, x1 mega2560, 2x single encoder, 2x buttons and make my own faceplate manually or with 3d printer. good luck.

remember to connect GND and 5V to max7219 individually, not in series.
and according to sismo website. there also SC version of the nav module with different pinouts for simcard controller only.

Stephan - I wonder if the SISMO documentation is confusing. Perhaps pin 10 (the "common gnd") is fed to each of the segments separately on the PCB in a way that works. Otherwise, as Pizman suggested, we wonder how it works with a SISMO card?

Paul

Thank you thatchi, a wonderful explanation for the connections.

Paul, just follow the description of thatchi.

To your question, how does this work at SISMO. SISMO has its own bus system, which is not compatible with the MAX7219.
Since you only have the PCB for the NAV panel, you do not use the bus system from SISMO.
What I was not quite clear was the connection of the cathodes for the individual segments, but thatchi has worked out very nicely.

So what you need are the segments A-G + DP for each tube and the cathodes for the individual digits. That's what thatchi also described. If you do not know, where the individual connections are with the tubes, look a few messages beforehand, as the diagram of the tubes is shown.

So you have to make the (mental) connection from the SISMO connectors and PCB to the MAX7219 and the tubes. The Data lines comes from the MEGA. Once you realize that, you can connect the soldering iron.

Thank you thatchi and Stephan,

My eyes must be missing the difference between what thatchi described and the SISMO documentation. So nothing needs to be cut on the Sismo board? Pin 10 is still a "common ground for pins 1 - 8" ????

What has changed since we started this discussion?

Many thanks,

Paul

No need to cut nor modify sismo circuit board, indeed you should not , to keep its warranty . It just output of 2x 5digit led and input of dual encoder and 2x button switches prewired to P1 and P2 at the back, and a bunch of led for back light using 12V. You have to connect it to some source of control bus, like simcard or leobonar or in your case , MF. You can use 2x ribbon connectors , 40 pins and 10 pins, to P1 and P2. The other ends of connector P1 will need to attach to 2x max7219 for frequency display, which in turn connected to mega2560. P2 will need to connect directly to mega2560. You now can setup outputs and inputs devices with MF connector and do your testing. I would use pin 20 for common GND of display 1-8 and pin 40 for common GND of display 9-16.
Good luck. Let us know the results.

Here the pinouts from sismo

Okay, so unless I'm missing something in the translation, we're back to following the original Max7219 scheme with the published SISMO wiring document - ignoring any of the "common ground" issues Stephan noted? (thatchi's description is just the SISMO wiring document that I linked in my original post, nothing new).

If so, I will buy another cheap max7219 IC tomorrow and breadboard this while waiting for my 2 x 4 modules to arrive from eBay.

I'll let you know how things progress.

A couple of questions: Is it necessary to connect the encoders to test the segment displays? I assume I can use the "test" function in Mobiflight to see if the displays work without the encoders or buttons connected. Also, should all of the ground connections (two on the Max7219 IC and 4 on the SISMO card) be connected to ground on the Mobiflight?

Paul

Hi Paul,

forget the the things with the GND. I think that has confused us a bit.
If you wire like thatchi's description you will have success.

You use the SISMO PCB for the components but not the SISMO logic to display. That is now your MAX7219. 3 wires from your MEGA (pins of your choice) to the MEGA (DIN to MAX pin 1, LOAD/CS to MAX pin 12 and CLK to MAX pin 13).

Wire the GND from your MEGA to the SISMO-board and from MEGA to the MAX7219. Pins 4 and 9 of the MAX (GND) can be wire-bridged.

You're right, for testing use the Test-Button within MF. If you have defined 5 Digits to be shown you should see then numbers 123.45. If you see 543.21 you have to change the digit assignment. Swap 1 with 5 and 2 with 4. 3 can be left. Note: these lines are the cathode-lines not GND lines.

I know, it sounds a bit confusing but if you have it understand it should be all clear.

The encoders, switches and LEDs can be soldered on the SISMO-board but are to be wired from the socket to your MEGA and the predefined pins (definded and named as devices in MF)