Casio Revives Innovation with RPN Calculator and VFD Clock

Innovation from a Vintage Casio Calculator

Have you ever heard the phrase "the problem is the solution"? This concept seems to originate from the permaculture movement, but it can easily apply to the electronics domain as well. Let's consider the challenge faced by [shiura]: a Casio Mini CM-602 that became irreparable. The solution was a clever combination: reconstructing the Casio calculator into a modern device with Reverse Polish Notation (RPN) and repurposing a VFD display for a WiFi clock.

[Shiura]'s documentation provides a useful guide for understanding the battery of this type of VFD, in case you don't have the same model of calculator (or VFD tube) they are using. If you have undertaken such projects before, you know what to expect: you power the device and cut the power from the pins one by one, mapping which segments or characters turn off, thus identifying the anodes and cathodes. The cathodes were already identified based on the PCB layout. After that, all you need to do is connect the VFD to an ESP32 via an array of transistors to achieve the correct voltages, and voila! You have a clock.

The code and design files for this clock—including an editable .blend file—are available on GitHub. The calculator aspect of this project is an incredibly elegant hack, based on the fact that the Casio’s CPU shares the same pin pitch as modern microcontrollers: 2.54 mm, or 0.1 inches, so a zero RP2040 can fit in the original CPU footprint while scanning the keyboards with GPIO. Then, an I2C display is connected separately to replace the VFD.

Perhaps a driver circuit for the VFD broke, or [shiura] salvaged the display before deciding to save the calculator, as there seems to be no reason why this brain transplant couldn't have been accomplished while retaining the original display. I admire the fact that having two lines on the screen instead of one makes the new calculator a bit more usable. The code for this is also available on GitHub, and although the documentation is in Japanese, automated translations have improved significantly, and the code is quite readable.

Long-time readers are likely familiar with [shiura]'s work, having seen numerous fine clocks presented by this creative Japanese individual, alongside vintage calculator repairs. The union of these two projects makes this dual hack a true representation of their style.