MobiFlight Community Support

Hello,

I'm hoping someone with electronics expertise might be able to help me.

I'd like to connect a SISMO Nav Radio module to my Mobiflight driven Arduino. The product advertises itself as "Arduino compatible" but "requires a specific board to control 7 segment displays".

The SISMO module is well documented at the page link below, which includes a link to the wiring schedule for the input and display (note, there are two different schedules, one for using the SISMO interface cards and one for "other").

https://sismo-soluciones.com/en/modules-idc-interface/141-1715-nav-panel-module.html#/32-dzus-yes_4_units/141-led_display_color-amber/174-digits_per_display-5_units

I've had good success interfacing standard items to mobiflight so far, but this one has me confused. Is there some sort of 7 segment control board I need to buy that goes between the Arduino and the outputs on the SISMO module? If so, I then need to understand what this might be, and then understand the pins that correspond to it (I'm used to the simple 7 segment display with 3 data lines, ie the MAX7219).

Maybe it's a bit of a mystery, or it's something everyone understands except me. Either way, it might be a useful to figure out for the benefit of others in the community.

Many thanks for your help in advance,

Paul

Hi Paul,

if you know the MAX7219's wiring, you're on the right track. Maybe you also have a board with the MAX7219 and the attached digits (2 x 4).
Otherwise, you can buy them at ebay.com for less than 2 Euro / piece. The boards with the attached Digits are green! The blue or red boards are soldered in place.

Important for the SISMO manual is the variant under 6.2.2 with the CC in brackets. CC stands for Common Cathode.

How the segments and the digits are wired, you can see here:



Thus you can go from MobiFlight with the 3 lines (in addition also GND and + 5V wire) to the MAX board and of the IC-versions (necessarily with the boards make sure that the Digits are pluggable!) To the appropriate connections of the SISMO boards or plug.

However, you will not get along with one MAX board because you have 10 digits. Therefore, it is recommended to connect 2 MAX boards with 5 digits each. You can ignore unnecessary connections at SISMO. Make sure you have 7-segment digits with a common cathode, otherwise it will not work.

Attention: The SISMO board has only 1 common cathode for the displays (Pin 10 : Common GND for Pins 1 to 8). This will not work because the cathodes are driven via multiplex. So you have to figure out from the digits which is the common cathode of the digit and to wire them from the right. From the right because this is the 1st digit, the 8th digit is the left (seen from the front). Wire these 5 wires (Digit 1 to 4 from the right IC socket and Digit 1 from the left socket [5th digit]) accordingly. Eventually, you will have to cut on the SISMO board PCB tracks so that each digit can be controlled separately. Also check if the tracks are really completely disconnected and there is no connection to their GND, otherwise you will destroy the MAX chip! Test with continuity tester or multimeter. This applies to every digit. the cathodes must not be in contact with each other!

For the MAX boards, either remove the D1 (each) diode and replace it with a jumper or wire each MAX board individually to the 5V of the MEGA.
Background to the diode is that with each diode in the board chain (if only 1 times 5V is connected to the 1st board), the 5V on each board reduce by 0.7V and already a 3rd board would not work.

If you've done it all right, your panel should work. If you have any questions, just go ahead. Please report the result.

The Manual still show the needed Pins for the Cathode Lines, i think.
Pin 10 /20 and Pin 30/40 is not needed cause these are CC.

If i undertnd right the Key is Pin 11-15 and Pin 31-35

Use TWO Max7219 with removeable Diggits.

Max 1 is wired SEG A - SEG G and DP to Pins 1-8 .... SEG 1 - SEG 5 (Check from Rigt to Left) to Pins 11-15
Max2 is wired SEG a- SEG G and DP to Pins 21-28.... SEG 1 - SEG 5 (Again Right to Left) to Pins 31-35

Thank you so much for your detailed responses. I think I'll be sending the Nav Module back to SISMO. While the MAX7219 connections make sense (more or less), I'm less inclined to go this route given the common cathode issues and the need to cut tracks on the SISMO circuit board, not to mention buying and modifying additional MAX boards. This was not on my mind when mistakenly ordered the module (which I thought would connect directly to Arduino). Note to self - 'read the fine print').

In fact, it would actually be easier for me to build the radio from scratch, using a 7 segment display with MAX7219 already attached (as I've experimented with in the past). It's a pity that there isn't a more 'plug and play' option to interface the SISMO radio modules with Arduino.

Thanks again,

Paul

PS - If SISMO don't accept the return, I'll be back with more questions ;-)

PS - an option (to be verified) from SISMO:

https://www.aliexpress.com/store/product/TPIC6C596-CJMCU-8-bit-shift-register-displays-7-segment-7-segment-digital-tube/2632035_32788252564.html?spm=a219c.12010108.1000001.12.302c676anzLsQu&ws_ab_test=searchweb0_0,searchweb201602_3_10065_10068_10547_319_10891_317_10548_10696_10084_453_454_10083_10618_10307_10820_10821_10301_10303_537_536_10059_10884_10887_321_322_10103,searchweb201603_52,ppcSwitch_0&algo_expid=25458b1d-c236-4d29-9c6f-1bd86e139e9a-1&algo_pvid=25458b1d-c236-4d29-9c6f-1bd86e139e9a&transAbTest=ae803_4

Don´t mix up 2 facts....

In the description the talk about compatibiltiy with "Arduinio" .
At the moment you install Mobiflight Firmware the Arduino is no longer technical a Arduino..... It change into a Mobiflight Board !

So your linked part will work if you write own code via Arduino IDE scripting language.... But it will NOT work with Mobiflight.

So its pretty simple.... If you like to use Mobiflight to get Data from Sim to your Hardware then the ONLY way is to use Max7219 Chips.
Thats no fault from Sismo..... They can´t know what software you use ( Normaly cockpitbuilders make there own scripts so thats not important for Sismo)

At least.... Not be affraid.... Wire the installed Displays with the included Pins on the Sismo PCB to a MaxChip ( with removeable Diggits) is not difficult. This is done in less then one Hour, and need not much knowledge.
So if you like to use this Element simply order 2 Displays and solder this stuff together and it will work fine !

It's less about fear, and more about time and motivation. But your point is taken. I have a couple of spare 7219 segment displays left over from some previous projects, and I'll revisit the idea when the module arrives. In the mean time I need to dissect a little more the information on common cathode issues. Did you have a look at the board on that link I sent? Any thoughts?

Hi Paul,

your link contains only the driver board for 6.5" digit 7-segment driver (16,6 cm!!). This can't be used with MF.

Take this one or one like this:

https://www.ebay.com/itm/Black-Red-Blue-Board-8-Digit-Tube-MAX7219-LED-Display-for-Arduino-Raspberry-Pi/132589933852?hash=item1edef9d51c:m:m83YdvwicqiZdnFLdLy7M6A

and take ONLY the green ones (green board - they only have the removable tubes)

Okay - thanks Stephan. I thought the suggestion from SISMO looked a little odd.
Much appreciate your recommendation - I've just ordered a few green ones. Stay tuned ...

Paul

Hi guys,

Just to clarify - wiring of the "5th" digit is to DIG1 on the left socket, correct? Do the display segments (A to G and DP) need to be wired into both the left and right sockets - or just the right?

With regard to power, I'll likely just wire each board directly to 5V, and save myself the "diode surgery". I assume that's okay.

Now, the tricky part. Apologies, but I'm still unclear on the common cathode information - the need to cut tracks on the SIMSO circuit and so on. Sorry for my lack of understanding of this, but can you explain this in more detail?

Thanks again to you both for your information - and particularly the picture of the 8 digit Max7219. I've found an additional resource that may be of interest to the community here:

http://www.learningaboutelectronics.com/Articles/Max7219-4-digit-7-segment-LED-display-driver-circuit.php

Paul

Hi Paul,

you're right. DIG1 from the left socket is the 5th segment-line.
And no, the display segments need not to be double wired. The segments of all 8 segments are wired on the PCB. You know you have two blocks with 2x4 7-segments and these two blocks have to be wired if you put them into the sockets. If you wire all segments with the 1st block and you wire to your own segmets, you only need to wire from the 1st block.

It's ok to keep the diode if you wire each PCB with a separate wire. GND you can wire ffrom PCB to PCB but may also be wired separately.
If you keep the diode your board will run with 4.3V instead of 5V but this does operational not matter.

If you have a look on the SISMO-PCP you should identify the segments first. A-G and DP. The identify the GND-line. This should be one line from digit to digit. This line is to be cutted off on both sides of the digit so that are absolutely separated (also from GND!). They are then "hanging in the air" with no connection to nothing. Here you have then to solder the single digit wires (1...4 from the right block and 1 from the left). Hope this is understandable...

Your link is ok but on the small PCBs there are SMD-Chips mounted. Same pin-layout, but more difficult to solder. The code of the link can be ignored.

Please teach us about your progress.

Hi Stephan,

Today I bought a cheap Max7219 IC and mounted it on a breadboard. I wired up the segments and digits according to the SISMO guide and the Max7219 schematic, connected it to Mobiflight, and attempted to test. Of course, nothing - no doubt because of the grounding issues. Perhaps I've blown the IC, but it was very inexpensive test that proves the logic ;-)

I'm still not quite sure what to "cut". On the SISMO circuit board, each of the two 5 digit displays (nav active and nav standby) is push mounted to a socket which is soldered to the board. It is easy to remove each digit 'bank' from its socket. Each bank has 14 pins (7 on top, and 7 on bottom). Are you suggesting that it is one or more of these pins that can be cut? Otherwise, the task will be difficult. Identifying and cutting the very small tracks on the circuit board (some very close to others) could be a challenge.

Many thanks for your continued advice,

Paul

https://static.wixstatic.com/media/031b6b_80610c9d18fb4790894b35349a8765cb~mv2.png/v1/fill/w_612,h_204,al_c,lg_1/5%20DIG%20WD_PNG.png
Here the wiring 5 digit to max7219. It is from the site 727diysim.com. It is a wonderfully detailed how to make home cockpit with MF. He use prosim737. Hope it helps. Good luck.

Hope the pict shown. Sorry the site is 737diysim.com

Go to getting started section and read 7segment display. As well as encoders. You need those to rewire the sismo.