New project: Pocket Calculator

Recently I got interested in building a very small calculator I can carry around with me. The other calculator projects I worked on are neat, but I don't carry them around because they are too big and fragile. This time I want to make something really practical but also small enough to fit in my pocket. The smallest way I know how to do this with the chips I'm familiar with is using the same LPC1114 in DIP28 package I used for my Programmable RPN Calculator. There are a few changes I would like to make for this calculator, though. First, I want to be able to manipulate all kinds of data on the calculator's stack, such as strings, instead of just floating point BCD numbers. Second, I plan to redo the BCD format I used in the other calculators to store the least significant digits first, which should make them a little easier to deal with. Third, I plan to make all items on the stack variable length, rather than fixed length like on my other calculators. This will be necessary for this calculator since I plan to store the whole stack in the 4k RAM the microcontroller has, instead of on an external SPI RAM chip.

The main new feature I want this calculator to have is a BASIC interpreter. My experience with the first RPN calculator I worked on showed how much of the microcontroller's flash can be eaten up by interface code, so I really don't think I could fit all the calculator functions and interpreter in the LPC1114's 32k of flash. Instead, I plan to store a virtual machine on the chip that can interpret code stored on a large capacity flash or FRAM chip. Retrieving the code over SPI and interpreting it will be much slower than executing code natively on the chip, but I think it will be fast enough for the UI, BASIC editor, and maybe even the tokenizing part of the BASIC editor. On one hand I could switch to a chip with bigger flash, which I am not anxious to do, but I will need some kind of virtual machine anyway to interpret the code generated by the BASIC editor, so it is no loss to use the same virtual machine for the UI. The BASIC programs and editor data will be stored on an SPI SRAM chip, which should work fast enough to edit and tokenize programs, while all the stack and program variables will be stored on the microcontroller.

Summer Hackathon: Conclusion

The Summer Hackathon I started on in May came to an end in August when I displayed a lot of what I had been working on at Makevention. I finished some projects and abandoned some others. Here is the outcome of the projects I set out to work on.

EEPROM Computer	Progress:	Abandoned
As I mentioned in the last update, a 4-bit version of this kind of computer has already been made by someone else. In the future I may make a 32-bit version, but for the time being I am done working on this.

8-bit Homebrew Computer	Progress:	20%
For this project, I designed a lot of the opcodes and most of how I want the computer to work. The chips I want to use don't seem to be simulated anywhere, so I will have to breadboard everything to test it out. So far I have one chip working just to test how it works.

Brainfuck Microcontroller	Progress:	55%
Apart from a few counters and status LEDs on a breadboard, I started soldering some boards with double row headers to hold everything.

Juggalo Robot	Progress:	70%
During the summer I didn't make much real progress on this project. I spent most of my time working on projects for Makevention instead.

ESP8266	Progress:	50%
I got an ESP8266 up and running. At first I had problems with the power supply but the chip seems to run alright with those problems solved. It also lists and connects to networks. Next, I need to connect to a server and transfer data, which will be used for a calculator project.

Wireless Breadboard	Progress:	Failed
This project was a failure. First of all I made a mistake with the spacing of the headers and it wouldn't fit the breadboard I was using. When I was working with it later I broke the entire header in half. The project wouldn't work anyway because the breadboard drops so much voltage. Unless I can find a breadboard that is much better, I don't intend to work on this project.

ATF1508 CPLD	Progress:	Done
After a lot of trouble and replacing a bricked chip, I eventually found a way to reliably program this chip. I also soldered a board to use for testing. This should be everything I need for the project I will use it in.

BASIC Interpreter	Progress:	30%
I also didn't make any progress on this project either. It would have been used with the Wireless Breadboard project if I had finished it. I will keep it for a later project I might need BASIC for.

LCD Programming	Progress:	50%
I got an LCD working for the 6502 Graphing Calculator project, as well as a VFD (technically not an LCD) for the Improved RPN Calculator. I did not get the LCD on the STM32F429 Discovery board working because I didn't need it for the Improved 6502 Trainer. I also haven't gotten the monochrome 5.5 inch LCD that requires -27v working yet. It will probably be easier to get a color LCD of that size instead.

Improved 6502 Trainer	Progress:	Done
I finished just about everything I wanted to for this project. It is much faster than the first 6502 Trainer. I will use it to develop for the 6502 Graphing Calculator.

Improved RPN Calculator	Progress:	95%
I finished almost everything for this project except a permanent keypad. I also renamed the project "Programmable RPN Calculator." The keystroke programming can repeat keystrokes, but it can't do any testing or branching. I will add those features eventually, but not in this version of the hardware. I shrank the size of numbers from 255 bytes down to 140. This lets me store all the temporary registers used during calculations on the chip, which makes calculations about five times faster. When I make a keypad I will be finished.