Introduction: USB48G - Upcycle Broken Hp48 Keyboard

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:

hp48 Backside Circuit:

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

The project is build on: and

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.

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.