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DIY prototype RPN/TENKEY programmable calc with printer <:3)--
11-08-2019, 06:46 PM
Post: #1
DIY prototype RPN/TENKEY programmable calc with printer <:3)--
Hi everybody. Some time ago (many years in fact) i found some HP calculator emulators on the web. I found that RPN system can be kinda good for some things, especially for programmable calc. I started to get interested in HP calculators and soon i started to look for some 48GX or 41CX, (un)fortunatelly it was not easy to get one in Poland, and prices of the ones on Ebay were a little too high. I ended using emulators on Android and PC.

Some time after that i just started to think if i could make a calc by myself. I had done some experiments with my own software calc using tenkey system. Then i got some cash registers for parts and i made functioning thermal printer out of that parts. When i got printer i though to myself that i am only missing a good calc to connect it to it ;-) I got some mechanical keybaord modules, LCD displays and stuff like that and i found that those parts are great material for a calc.

I started looking for MCU to handle that stuff and found that AVRs may not be the best choice, i found cheap STM32 board and i found it great for the job. From the lack of pins i used old AVR just to work as keyboard controller. It took many software upgrades to get to the state where i am today, i have learned some things along the road. Software i written is in Bascom (for AVR) and Arduino IDE for STM.


Here are some of the features of the junk i have made:
-RPN/Tenkey system with 6 level RPN stack and 2 Tenkey adders. * key is used not only to clear tenkey adders but also can move data from adders to RPN stack.
-Can swap any 2 levels of stack (not only lower ones).
-Indirect memory access with STORE, RECALL, ADD (shift + left add button) and SUBTRACT (shift + left subtract button) functions.
-Build in unit converter and constant library.
-Various scientific math functions hidden in >MATH< menu.
-Alphanumeric prompting (on LCD) and printing.
-Printing on thermal printer, trough universal UART (for Psion Workabout MX) or USB (emulating HID keyboard or USB UART).
-Shadow and normal programming (shadow mode works like manual operation, but it stores everything you do in background, so the keypresses are both executed and stored in memory).
-5 programmable keys.
-Statistical functions.
-Timer (much like HP-41CX one) that can be triggered manually or by external interrupts.
-Possibility to read values from ADC inputs.
-Multiple display modes (showing things like whole stack, part of stack and tenkey adders, part of stack and alpha registers and so on).
-Dropping values from stack to PC (trough HID USB keyboard emulation).
-Values can be displayed in SCI format or in fixed point (rounded) format, but they are always handled as 64bit floating point.


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11-08-2019, 10:20 PM
Post: #2
RE: DIY prototype RPN/TENKEY programmable calc with printer <:3)--
Very cute, but also really impressive!

A blue wire is not connected, you’re gonna lose digits Smile
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11-08-2019, 10:57 PM
Post: #3
RE: DIY prototype RPN/TENKEY programmable calc with printer <:3)--
Blue wire is for STM32 default UART bootloader. It is used to program the chip. You connect it to the USB>UART interface and you can load the program into the chip. You also have to flip that switch below it (and obviously change the jumpers on board to put STM32 into bootloader mode), because normally pin RX1 is used to receive data from ATMEGA-16 that is the keyboard controller. So the blue wire is normally not connected to anything, because when switch is flipped left, RX1 goes to ATMEGA and not to blue wire.
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11-08-2019, 11:28 PM
Post: #4
RE: DIY prototype RPN/TENKEY programmable calc with printer <:3)--
Hello!

Very cool project! I especially like how you finally found the ultimate solution as to whether the basic + - * / keys belong on the left side or on the right side of the keyboard: You simply put one of each on both sides :-) I hope you applied for a patent for that, otherwise we will see it on all future calculators of HP. TI and Casio...

Regards
Max
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11-09-2019, 02:49 PM
Post: #5
RE: DIY prototype RPN/TENKEY programmable calc with printer <:3)--
The keys on the right are for tenkey operations. Without shift they affect tenkey adder no1, with shift they affect adder no2. * key is quite funky. First press basically pops the adder's value on the RPN stack, second press clears the adder (just like it used to do on those office calcs).
Above tenkey keys there is a key for adding into statistical registers and one for entering into alpha mode (for programming the ASCII text).

On the left there is a RPN section, those keys affect RPN stack. + and - keys can also affect memory when used with shift (memory add and memory subtract).

There is also multifunction encoder. It can be used to select display mode, ammount of decimal places to display, scroll the program listing, select memory cell holding time of reference for stopwatch mode or scroll the ASCII list in alpha programming mode.
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11-09-2019, 04:52 PM
Post: #6
RE: DIY prototype RPN/TENKEY programmable calc with printer <:3)--
Hope you could send a few videos to demonstrate those functionalities.
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11-09-2019, 05:50 PM
Post: #7
RE: DIY prototype RPN/TENKEY programmable calc with printer <:3)--
I have that in my plans.
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11-10-2019, 04:53 AM
Post: #8
RE: DIY prototype RPN/TENKEY programmable calc with printer <:3)--
Great work!
And RPN machines made in Poland--> just makes good sense!
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11-11-2019, 05:02 PM
Post: #9
RE: DIY prototype RPN/TENKEY programmable calc with printer <:3)--
Here is some demonstration.



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