Hello, I'm trying to build a 737 MCP with multiple 7-segment single digit displays. I have a problem when I chain them all up. I think I followed all the wiring diagrams in the site but I'm new at this. I'm getting sometimes good indications and some other digits do not light up at all. I've checked all the wiring and seems to be OK. Sometimes the three digits representing Coarse1 change to Heading when I rotate the heading knob. Can I chain all the D and L lines? Can I chain VDD? and ground? I was wondering is this wiring is OK I very new to electronics. Thanks in advance, Juan.-

PS: I've tried to illustrate some part of the circuit below.

May 21 in General Questions by

1 Answer


It seems everything OK with your connections (all D and L are common and S are separate assigned to 3 outputs).

How are you powering your circuit? Do you use the 5V from the master board pin?
Maybe you need to use separate power supply for the +VLED (leaving the +5v for the driver chips only)

P - by the way, you can connect in chain up to 4 drivers (not only 3 as pictured here as example: https://simvim.com/tech_num.html  and use one output instead two for two parameters on one 7-8-digit display

May 21 by
Thanks Vlad for the quick response!

I'm powering the whole circuit (IC's and all) with an old AT PSU as you suggested back when I started in november (great idea by the way!). It says it has 25A on the 5v rail and i'm guessing it should be OK for the whole MCP. Is it Ok to chain +5v like I've shown? and ground? I read in the "common ground" section that you should have one big AWG wire with all the grounds to it in order to reduce flickering of LEDs. Regretfully I've seen this note once I've finished connecting all the stuff. I have all the buttons, leds, ICs, etc "daisy chaned" (i think that's the correct expression as english is not may first language). Maybe that's not good and causes this inconsistencies with the displays? Anyway thank very much for all your work that helps the flight sim cockpit builders around the world!