Wooden RPN Calculator

A RPN (Reverse Polish Notation) calculator of billet walnut case.

• There are multi-functional RPN calculators with numbers of small keys. However, daily use RPN calculators with large and light touch buttons are rare. So I made it by my own.
• This calculator also has trigonometric, logarithmic and exponential functions. It is hidden but appears on the LCD as function key style by pressing the silver key (or long press of keys).
• Comfortable and traditional look made from wood billet.

Supplies

The schematic diagram and case design depends on what parts you select. The following data (STLs, gcodes) are just for my case. I used

• USB Numeric keypad (I used Buffalo BSTK08MSV)
• Dot matrix LCD display (I used IIC LCD2004 type LCD)
• Arduino nano
• DC-DC up converter (3v to 5v)
• Walnut billet wood
• Blank PCB
• Acrylic plate
• Short parts (screws, electric wire, solder, etc.)

Step 1: Reverse Engineering of Keypad

• Disassemble the keypad.
• Check how the switches are connected to the PCB. In my case, the conductor on a film and PCB just contact with some pressure of rubber tip.
• Check the wiring (key map) of the numeric keypad.
• STL file of the green parts (holder of rubber tip ) can be downloaded below (rubberholder.stl).

Step 2: Test the LCD Module

• Connect the LCD module to your micro controller.
• Flash the test code supplied by the LCD module manufacturer to the micro controller and watch what happens.

Step 3: Make PCB

• Make PCB to connect the micro controller and the keypad.
• The PCB is also used to support the keypad to the case (body).

Step 4: Design the Case

• Design the case using your CAD software. I use Blender to design the case.
• The case is also designed to cope with CNC machine. The corners of the pockets are rounded to use 4mm square end mill.
• Print the case and test it.

Step 5: Machine the Case

• To machine the case, I used 4mm square end mill because the radius of the shank is same to the end of the mill. It can machine deep pocket and vertical walls.
• Attached files are the examples of the tool paths.

Step 6: Machine the Window

• Machine the window from an acrylic plate.
• To suppress heating, I use drops of the water.

Step 7: Asssemble

• Apply oil stain to the case.
• Assemble the all parts.

Step 8: Flash the Code

• Flash the RPN calculator code to the micro controller.
• (Nov. 11, 2022) quick-response.ino is added. This code is ready for quick input with fixed 3 level stack display (internally 12 levels).

Step 9: How to Use

• You can use it with RPN style operation.
• Functions appears with long press of keys or silver key.