clockworkpi

DevTerm 40-pin Expansion FPC Connector: All Pins in Use?

The DevTerm’s expansion connector breaks out the same 40 pins as seen on the Raspberry Pi.
I’ve been looking over the schematics to see which of these pins are free to use. However I cannot seem to find any that aren’t accounted for. The image below shows the standard 40 pins (with raspberry pi labeling) and the DevTerm usage of those pins. As you can see, if you want to use any of these pins for something else, you may be out of luck, or you may have to give up functionality somewhere.

On one hand, it’s neat to see that you can interface with the Wifi/BT chip, the audio out, and headphone detect with this cable. But if these are all used up, I’m having a hard time imagining what to do with this expansion port. It seems like the best place for additional hardware expansion is using the Ext port with a custom Ext module.

Take this info lightly! I’m not an expert, just someone combing through the schematics and trying to wrap my head around things.

Pi vs A04/06 note: For in both core module types these 40 pins are all still taken up. The only difference may be that the pin functionality (eg I2C, SPI, etc…) might be different on the A04/06.

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I’m starting to wonder if it would be possible to disable Wifi/BT. This could potentially free up 19 pins!

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i got a fpc gpio breakout to mess with this regardless. you could still use the pins, but if anything else is active, youll get all kinds of interference (which may be worth exploring…) I do imagine its possible to switch the radio off. If it is not on and not in use it cant do harm, right? I’m not terribly worried about the possibility of losing an option temporarily when i have so many dongle and adapters about. some that dont even need nexmon.

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I was just thinking…if one does not need the thermal printer, one should be able to use those pins going through the Ext module, and break them out right through the back where the printer goes, right?

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check out my mans custom ext breakout

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Yep…something like that :slight_smile:

Thanks.

Yeah that would be ideal! But the unfortunately the printer FPC connector isn’t just GPIO/data lines. Several are drivers for the printer motors. Buried in the tinker thread I mention that I have plans to design an EXT board revision that keeps the printer and usb functionality, but reworks the printer ribbon cable to be general purpose (this would involve a separate driver board for the printer). After a revision, the 24 pin FPC connector would be replaced with a 40 pin “pi-hat-safe” FPC connector.

Here are those 24 pins for the printer FPC connector so you can see for yourself that they aren’t really usable GPIO/data pins:
Screenshot from 2021-06-14 15-08-03

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I wasn’t necessarily thinking all the pins could be used, but to communicate with the CPU at least a few should be freed up.

And yes, I think designing an EXT board that keeps the USB ports is a good idea. That’s actually the only disadvantage I see with the breakout you already showed in the other thread.

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