Updating My Sim Wiring

Last Saturday saw a friend come around to use the sim. You may have seen Dan use the sim several times before. This time he wanted to move away from manual flying and try programming the autopilot from Amsterdam to Stanstead. As we were sat there mid-flight several glitches started to appear. The first being loss of the 7 segment displays on the MCP after about 30 minutes of sim operation. It started with the Captains course display which went blank, followed by several other displays on the MCP. Usually, a MobiFlight restart will correct this. However, the fault just appeared to get worse. Looking back the MCP was created in 2015 and has worked flawlessly until now.

Poor Soldering & Wiring

As I had to take the glare shield apart to replace the Captians EFIS with my new 3d Printed EFIS. I thought I would take a look at the MCP to see what was causing the issues. It didn't take long to see that the wires from the MAX7219 boards had become detached. There were various wires that the flux had corroded through the cheap 3 stranded wiring with the humidity out here and being outside for several years. It certainly wasn't helped by poor soldering on my behalf.


I then realised, if I wanted a reliable unit again moving forward, I needed to replace all the wiring in the MCP. This is where I had to stop designing the new motorised throttle and take a step back to ensure the sim was once more operational while I designed other parts. Late on a Sunday night, while listening to an audiobook and armed with a Tiger Beer, I desoldered all the wires to the MCP.

Audiobook -Check! Tiger - Check! Lets do this!

This was slightly soul-destroying, and all I wanted to do was concentrate on the new design-build. But as I removed the cheap wire, the realisation set in on how bad using the really cheap wire was. I mention this on the website several times about the cheap Chinese wire from eBay. I usually ordered 100-meter rolls when I started out. I would order from several different suppliers until I found one that supplied semi-good quality10-15 strands at the same price as the 3 stranded wire. Instead of not using the 3 stranded wire, I opted to use it in places I thought I could get away with it, where there was no movement of the wires. This was mainly the MCP and Forward overhead. 6 years down the line, both of these are now suffering from malfunctions.

Luckily for me, the aircraft modifications team from Phoenix Aerospace saw my Instagram posts while they were working here in Brunei and offered me 50Kg approx of discarded Blackhawk aircraft wiring. This was an amazing gesture of both Phoenix and the Blackhawk operators. This has now allowed me to replace every wire in the sim with aircraft-grade wire.

The 737 MCP Rats Nest

It took around 6 hours to completely rewire the 737 MCP using the new wire. It may look a bit of a rats nest here, But that's just because I leaving long tails which get trimmed down to the correct length afterwards. During the wiring process, I moved away from daisy-chaining 7 segment displays completely. Each display now has its dedicated 3 data wires back to the Arduino. So instead of only using 3 wires for all the displays, it now takes 9. This should stop all the displays from failing when one display develops a fault.

During the wiring process, I really wanted to try something new. Wiring the MCP direct to the Arduino Sheild was okay and allowed for a reasonable quick disconnect. However, this time I wanted an even better solution. I certainly wanted to move the MIP Ardunios out of the glare shield to a place where the wiring was accessible with deconstructing the cockpit. (like the outside front of the cockpit) If I was going to make another sim, I would have a central locker or interface board away from the sim that all the connection/wires go to. This would cost more in wire, but the ease of maintenance, in the long run, would be worth it.

This is what I ended up with. Three DB-25 Connectors connected to the Arduino Mega via a prototype shield. This is how I will now create all connections from this point on. The MCP uses 73 Pins of the 75 Pins available. 69 pins (including the Analogue as digital pins), one 5v line and three grounds (one for each plug).


You can see that the LED lines on the prototype board have 100 Ohm resistors fitted which makes things much tidier, rather than fitting them to each of the components.

These Arduino's are now fitted to a 3d Printed mount and are placed on the back of the MIP for easy access. This allows the Qty 4, 10 port USB hubs to directly connect to all the Arduinos, Leobodnar and Leonardo Cards.

Labelled Wiring

Each of the DB-25 connectors are labelled with the connecting device. Then secured in a plastic hood creating a neat and tidy package. Once all the wiring was done, it was time to fit the EFIS and MCP. First up was the fully 3d printed EFIS (less the cockpitsimparts faceplate).

737DIYSIM 3d Printed EFIS

After the EFIS was connected and programmed, it was time to fit the rewired MCP. From the picture below several things can be seen:


1) MSFS2020 at Luka airport in Nepal at 4K is drop-dead gorgeous!

2) The MCP displays now work!

3) I still need to create the FO EFIS!



While I was rewiring the MCP, I also redesigned and printed all the Knobs for a better finish. The displays gained the black plastic rim to create a more professional finish.


3D printed display bevels

That's it for this week's unexpected detour! I can't wait to get back to designing the new throttle unit and test printing it. But for that I need to head over to Patreon and update the guys there, then answer Youtube, WhatsApp and Instagram comments!


Take Care,

Karl & Helen.




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