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I have used HP RPN calculators all my life. I wonder why there aren’t any RPN calculators anymore.
They have been phased out in favor of the standard infix calculators.
Anyway, I've always wanted an HP15c calculator and never got the chance to buy one.
So this is my take on building one.
It is designed with only through hole parts. For easy soldering.
The brains of the calculator is the ATMEGA328. It takes care of everything (display, keypad scanning, sound, clock, etc.).
I decided to use the ATMEGA328 since it is pretty common in the Arduino community and it is one of the few microcontrollers still produced as a through hole part. No other semiconductor is used.
Even though the ATMEGA328 is an 8 bit microcontroller and running at 8Mhz, it is still pretty fast. In the end, the emulation is about 4 to 5 times faster than the original.
I've added a speaker for audible Keyboard feedback. And a 32.768khz crystal for the real time clock.
The emulator can run any of the Voyager series calculator as well as the HP41C (my personal favorite!).
With the calculator turned off press the '.' button (Button '0' on PX41c) and turn it on.
Do not release the '.' (Button '0' on PX41c)button yet.
The display will turn on and show the version along with the mini-instructions.
When you do release the '.' button (Button '0' on PX41c), the setting will be shown.
Options that can be customized:
| Part | Value | Description |
|---|---|---|
| C1, C2 | 0.1µf | Decoupling Capacitor |
| C3 | 0.1µf | Speaker impedance |
| U1 | ATMEGA328P | Microcontroller |
| J1 | 6 pin female headers | PI Programing header |
| BAT | Battery Holder | CR2032 Battery Holder |
| SPK | BUZZER | Speaker |
| XTAL | Clock Crystal 32.768kHz | Clock |
| R1 | 10KΩ | Reset pullup resistor |
| R2 | 10Ω | LCD backlight resistor |
| BTN's | 6x6mm tactile switch 7mm height | Key buttons |
| RST | 6x3.5 mm tactile button | Reset button |
| DISP | Display 192X64 LCD | Display |
Current firmware version v0.85.
Download PX15c
Download PX16c
Download PX41c
Fixed/Added:
Firmware version v0.85:
Bugs:
Firmware version v0.81:
Bugs:
First Release: Firmware version v0.80:
Bugs::
Known Issues:
WARNING!: Pressing the reset key or uploading new firmware will erase all content!
To load new firmware, you need a standard AVR SPI (Serial Peripheral Interface) programmer. Such as the usbasp.
You can even use an Arduino Uno as a ISP programmer.
Also, you will need avrdude or some other software to program the microcontroller.
Most AVR programer have a 6 pin (2x3) or 10 (2x5) pin header. The calculator uses a 6 pin (1x6) header. So you will probably need to buy an adaptor or simply make one.
I simply cut the ribbon cable and solder a 6 pin male header.
CAUTION!!! Be sure the voltage on the programer is set to 3V, failure to do so will destroy the LCD.
RPN (Reverse Polish Notation) is a mathematical notation that allows users to solve problems by mimicking how they learned to do math on paper. The operators (+,–,x,÷) are placed after the arguments (for example, 3+4 becomes 3 {ENTER} 4 +) allowing users to stack number sequences and operations, working from the bottom up. RPN eliminates the need for parentheses in complex calculations and reduces keystrokes, making problem solving quicker and more efficient.
The LCD display has 12,288 (192x64) pixels. Enough space to draw all bitmap fonts along with the status bar. By the way, did I mention that is's backlit?
The ATMEGA328P microcontroller from ATMEL (now Microchip) is behind the PX-15c. It was chosen because of it's popularity with the Arduino community and it is still one of the few microcontrollers that is produced as a through hole part.
There is a standard magnetic speaker that is used as audio feedback on button pressed.
There are 39 standard of the shelf 6x6mm tactile switches.
Did I mention it has a real date and time clock?
You can always see the date and time on the status bar. The time heartbeat is provided by a standard 32.768KHz watch crystal.
Energy comes from one itty-bitty buton cell, a standard CR2032 3V, 235mah lithium battery that should last a long time with normal use.
To conserve energy, the PX-15c will speed down when ideal and will go to sleep after some time of inactivity. The backlight will also turn off after some time.
