This is a carrier card for an ESP32 DevKitC board that allows you to insert the ESP32 in between the TR1863 UART chip and the RS422 drivers.
This is currently pre-beta. It could have bugs. It might not work for you. It might fry your NABU. It might turn your dog into a geranium. I really don't know. Use at your own risk.
Also note that the firmware for this is currently being written, and all that is in this repository is code that shuttles bytes between the Z80 and the HCCA port, allowing it to boot when connected to a PC.
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An ESP32 DevKitC module. BE CAREFUL HERE! There are a couple of different modules being sold as DevKitC; but they have slightly different pinouts. Carefully check the pinouts in the product listing photos against the NABU-ESP32-TR1863 PCB layout before ordering a module. Also, some of these can accept an external WiFi antenna, and others have one built in. Unless you plan on running your NABU with the cover removed, I would suggest looking for one that can take an external antenna, and mounting that antenna in one of the expansion slot covers on the back of the NABU (to maintain originality, you might want to make a new cover plate either out of sheet metal or plastic; or perhaps 3D print one).
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An SD card slot module, such as is commonly sold for use with an Arduino. Like the ESP32 DevKitC module, there are a couple of different module styles available, so also check the product listing against the NABU-ESP32-TR1863 PCB layout before ordering.
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An SD card to fit in the module.
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The NABU-ESP32-TR1863 PCB itself.
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A 74HC4050 IC.
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A 1N4001 or similar diode.
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Decoupling capacitors in the range of 0.1uf to 1uf; two each.
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A 16-pin IC socket for the 74HC4050.
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A 40-pin 0.6" wide IC socket for the TR1863 IC.
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Headers for attaching the PCB to the existing socket on the NABU main board that the TR1863 is currently mounted in (machined round-pin headers work best, because they are smaller than the square-pin headers and thus won't bend the IC socket contacts as badly).
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Three each 400 ohm, three each 800 ohm, two each 120 ohm, and two each 2k ohm resistors if you want to use the VGA and PS/2 mouse ports.
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Female header sockets to put the ESP32 DevKitC module into.
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Male header pins for the VGA, PS/2, and SD card module ports (your SD card module may have come with these pre-installed - mine did).
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A 4 pin cable that connects the NABU-ESP32-TR1863 PCB to a 6-pin PS/2 mouse connector.
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A 6 pin cable that connects the NABU-ESP32-TR1863 PCB to a VGA connector.
Carefully remove the TR1863 UART IC from it's socket on the NABU main board. It's located near the DIN-5 RS422 port that would have connected to the NABU Cable Adapter. A proper IC extractor tool helps here, but it can be done with a small flat screwdriver if you are very careful.
After soldering the sockets, headers, and SD card module into the NABU-ESP32-TR1863 PCB, install the 74HC4050 IC and the TR1863 UART IC into it's socket on the NABU-ESP32-TR1863 PCB. CAUTION: Be sure to install the ICs in the correct orientation - especially the TR1863 as it is rather difficult to find a new one these days. Next, install the ESP32 DevKitC module into the female header sockets for it; also being careful about the orientation.
Using the round-pin header sockets on the far right side of the NABU-ESP32-TR1863 PCB, install it into the socket on the NABU main board that the TR1863 UART IC came out of.
Connect the ESP32 module to your main computer's USB port, and download the software for it. TODO: Create the software.