Scientific RPN Calculator (with ATTINY85)

[Maximilian Hohmann]

Hello deetee and Paul,

thanks for the workaround solutions for the EEPROM.put&get. However I decided to go a different path and installed a later version of MAC OS on an external disk (can't upgrade my computer permanently because I will lose too much precious software like Photoshop and MS office in the progress and also my printer is no longer supported in newer OS versions. And I certainly won't fall into the trap and buy all that again - this money I rather invest in my calculator collection) so that I can now run the latest version of the Arduino software.

Scary 2.0 compiles now and I could install and run it on my DIY calculator. Of course it only uses 1/2 of the hardware... But after switching it off and on again it did not start any more. Who knows why - maybe the Arduino nano handles it's EEPROM differently from the ATTINY? Not even re-flashing the board brought the scary calculator back to life so I guess it must be EEPROM related. When I have the time I will maybe try to debug the problem, the Arduino nano leaves me with over 20k of memory for adding debug statements.

In the meantime I went ahead with my "double-sized cheap Chinese display keyboard RPN calculator". As DSCCDKRC is too long to remember I now call it RLC16 (for Rpn Led Calculator with 16 digits). This leaves room for future enhancements because I bought enough of these boards to one day make an RLC32 :-)

The main problem I identified so far is power consumption which is caused by the large and bright displays - which are of course the main feature of the calculator! With all 16 digits displaying "8"s at maximum brightness the current draw from the battery is in excess of 400mA, closer to 1/2A even. The step-up converter is certainly responsible for about 20% of that but the alternative of using two such batteries and a step-down converter is not appealing. After all it is supposed to be a small calculator about the size of an HP-15C. Minimum power drain with all segments off is already 70...80mA (which could be lowered somewhat by removing the LEDs from the Arduino board or using a simpler board like an Arduino mini - or even the naked ATMEGA328P chip in the final version). So top priority is now power management. For that I will add an LDR to automatically adjust the display brightness and some kind of sleep mode which turns the display off after a few seconds of inactivity. Still the Battery (whose printed-on capacity of 6800mAh I don't believe for a second, not even half of that seems realistic) will last only briefly if forgotten to switch off, so I have to add a flashing LED as a reminder to turn the calculator off when not in use.

And I also decided that with the luxury of 32kB of memory I want 64bit floats and added the Float64 and Math64 libraries to the project, after all I want to add a GPS module at some stage and may need some precision. These math libraries together with the standard library of the TM1638 board use over 20kBytes already, leaving not too much room for fancy extras...