USB48G - Upcycle Broken Hp48 Keyboard

A guided upcycle project for a broken hp48.

By Michael (epostkastl). From https://www.instructables.com/id/USB48G-Upcycle-Broken-Hp48-Keyboard/

Reuse the keyboard and make it work as a standard usb keyboard.

Tested: Check youtube: https://www.youtube.com/watch?v=B3zB_xvoO4s

The video shows the keyboard plugged under Windows 10 running EMU48+.

Step 1: Open the Hp48

Opening the hp48 is not that easy. Be careful, you risk to crash you calc. I found the following documentations useful:

http://documents.epfl.ch/users/f/fr/froulet/www/HP/Opening%20the%20HP48.pdf

https://www.hpcalc.org/hp48/docs/opening/

https://users.ju.edu/hduong/repair/

Step 2: Checking the Connectors


The connectors on my keyboard have a resistance of

* 8 kOhm closed and

* 2 MOhm opened.

hp48 Backside Circuit: http://users.ju.edu/hduong/repair/circuit.jpg

hp48 Backside Circuit: http://users.ju.edu/hduong/repair/dome.jpg

Outputs: A9, A10, A11, A12, A13, A14, A15, A16, AR17

Input: A0, A1, A2, A3, A4, A5, ON-keyboard

Step 3: Correspondence Table

https://grack.com/writing/saturn/saturn.txt

Step 4: V-USB - a Firmware-Only USB Driver for Atmel AVR Microcontrollers

The project is build on: https://www.obdev.at/products/vusb/index-de.html and http://symlink.dk/projects/c64key/

Thank you for having brought the USB to the the atmega family

Step 5: First Circuit



The picture shows the first try. It worked out, therefore the wire-mess was never changed...

The usb plug subsitutes the serial plug. The ACRISP Plug is behind the IR-cover.

circuit-usb48g.pdf
circuit-usb48g.fzz

Step 6: Coding & Uploading



Attached the code. It works under AVR Studio4.

190410.zip

Step 7: Testing

The keyboard appears as standard keyboard and does not need any additional driver.