A guided upcycle project for a broken hp48.
Reuse the keyboard and make it work as a standard usb keyboard.
Tested: Check youtube:
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:
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
Step 4: V-USB - a Firmware-Only USB Driver for Atmel AVR Microcontrollers
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.
Step 6: Coding & Uploading
Attached the code. It works under AVR Studio4.
Step 7: Testing
The keyboard appears as standard keyboard and does not need any additional driver.