Recently I added a lot of panels to my home cockpit, therefore a cleanup on the wiring of the mainboard was very needed. So today I want to bring you a couple of insights on the rewiring process and rationale. The main change was meant to enable (at will) the interrupt mode. I also tried to maximize channel use vs daisy chains, to level out the amps requirements on each channel.
Introduction
The mainboard is very versatile, so it is the possible to run the satellites in several different modes, triggered by the PC, by the mainboard, or waiting that each and every satellite takes the action.
Polling the board
Up to now I’ve been using only four wires (SDA SCL GND and 5V) to connect each satellite with the mainboard. This handy way relies on USB cable and provides a convenient way to connect the boards in a clean fashion. Moreover, usually USB cables are shielded properly, and the wires gauge differ between power and data. As drawback four wire connection only allows the PC poll use, as well as provides some limitations on the maximum current the channel can provide. The current limit is due to the fact that the power comes from the mainboard to the satellites.
On the other hand, if one is connecting also the fifth wire (INT), the interrupt mode can be enabled. The mode takes advantage of a feature of the satellite microprocessor. In interrupt mode the mainboard simply waits for any input change at satellite level, which is communicated though the interrupt pin. Hence for rather populated systems, it is a way to reduce the Mainboard pcb overload. If an expander is used, psCockpit guide indicates that a 10kohm resistor shall be placed in parallel to 5V and INT (I understand it is to “pull up” the INT channel). On all custom psCockpit boardsother afore mentioned 10kohm resistor is embedded in the design. Therefore I applied the 10kohm resistor on the last item of the daisy chain if it was an expander.
Custom PCB
The mainboard has 8 channels, but on the pcb there are only 4 interrupt ones, so basically channel 0,1 2,3 4,5 6,7 are joined. To keep wiring simple (my mainboard is located inside the ICP case), I designed a very simple board, that basically shortcuts the channels’ interrupts. As always, refer to JShep for a lot more details on how to poll the expanders. As always, you can find the Gerber files for the PCB in the repository.
Final setup
My current setup has quite some satellites:
- Ch0 Landing Gear panel 111
- Ch0 Misc panel 010
- Ch1 Caution Panel 000
- Ch1 Indexers 010
- Ch2 TWP 110
- Ch3 ICP 000
Therefore I populated the first and second interrupts (0,1 and 2,3), moreover I made sure to put a common ground to every satellite, as I feed all the satellites through an auxiliary power supply, instead of feeding them all through the mainboard. Hopefully in this way the mainboard will have to supply less currents, and possibly last longer.
Jumpers
Once the INT and power supply was ok on all the boards, and the 10kohm resistors were added to the end of daisy chains expanders, I made the final mod to the setup.
In the psCockpit quick guide, it suggests, in case one does not use the input pots, to shortcut the connectors of the four channels. This operation can be achieved easily by means of jumpers. To do it in a clean way, I bought some of them on aliexpress, which I then installed on the board .
giovannimedici 
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