After starting on my 7400 Calculator project, I thought about how many projects I have open at the moment. Like a lot of hobbyists, I seem to start more than I finish. Most of these are not abandoned, since I do plan to get back to them someday. I decided to take stock here of how far I am and what is left to do. There are two projects here I have not posted about: 6502 Optimizing Assembler and 6502 Calculator Emulator. There isn't really enough yet to write about, but I might as well mention them since I have been working on them now and then for a while. They would also be good for the github page I want to set up and list when I apply for jobs. My plan is to finish most if not all of these projects before I start on something else. Otherwise the list might keep growing without finishing any of them.| Tiny Calculator | |
| A few weeks ago, I put a lot of work into the interface code, which ended up taking more time and effort than I imagined. Like in my RPN Scientific Calculator, the interface code takes up a lot of space compared to the math routines. So far, I can enter numbers and do addition and subtraction, but I still need to fix the sign of the result. For the rest of the calculations, I need to write a lot of checking code for things like scaling angles before applying trig functions and avoiding inputting negative numbers in logarithm functions. Two weeks ago I made some major progress with the keypad, which I will post about soon. Posts related to Tiny Calculator | |
| Pocket Calculator | |
| This project kind of stalled because I got busy with other stuff and also because I hit a few hardware problems that I did not solve. The LCD would work when the speed of the SPI clock was set very low and it would continue to work once I turned the speed up to what the LCD is rated for, but if I turned the calculator off, the LCD would not work again until I set the speed back to very slow. The LCD also did not work when I fully closed the case. Eventually, one of the very stiff ethernet wires I was using broke right off. I will need to rewire the LCD with different wire and start over on the emulator I was working on. Posts related to Pocket Calculator | |
| Programmable RPN Calculator | |
| The last time I worked on this calculator in 2015, I considered it finished other than labels for the keypad. One thing I figured out in the meantime is that the key reading is not entirely reliable since two of the pins on the LPC1114FN28 are open drain, which I did not account for. It also seems that I did not write the key reading code correctly, so there is a chance of shorting pins when you press two keys at once. These probably won't take long to fix, then I will make labels for the keypad, which should be easy now that I have done it for my Tiny Calculator. Another thing that might be helpful is to review the source code and make sure all of my checking code is correct. Posts related to Programmable RPN Calculator | |
7400 Logic Calculator
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This is my latest project and I have been doing a lot of work on it, so I am still really excited about it. I might try to finish some of the projects that are close to done before I return to this to get them out of the way.
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6502 Graphing Calculator
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In summer 2015, I put this calculator together very quickly to try to get it ready for Makevention that year. Not suprisingly, it did not work at all since I was in such a hurry putting it together. I'm not sure it would be worth it to resurrect this project, but I would like to at least return to it and figure out why it didn't work. One possibility is that the LCD was damaged when I was trying to drive it with an MSP430 since the wires I used had metal connectors that kept shorting to each other. Another thing I noticed when I pulled the board out a few weeks ago was that the EEPROM is not a modern CMOS chip but something older that uses 140mA and has a slow 250ms access time. The latches to drive the LCD are 74LS874s, which I now realize consume way more power than HC chips. There could also be other problems like the CPLD. In any case, it will be fun to try to figure everything out.
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6502 Optimizing Assembler
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This is a project I started to practice my Python skills and have a concrete project to talk about in job interviews. My plan is to analyze assembly files (not compiled binaries) and make optimizations based on a few simple assumptions. This will should be able to shave a few cycles off of unneeded instructions, which is especially useful when you are using macros. It will also be able to manage zero page much better than just assigning fixed addresses to each function or sacrificing the X register for use as a slow pseudo stack.
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6502 Calculator Emulator
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This is a 6502 emulator written in JavaScript that will let me test calculator firmware in the browser without having to upload it to a physical calculator. The emulation works at over 50MHz currently and passes Klaus' test suite. The input and screen output work, as well as memory paging like the real calculator will have. Now I have to find a way to speed up screen drawing, since I think this is the source of lag when typing. Then I will need to start writing the firmware for the calculator. Someday I will host it on a website so that other people can help me find bugs.
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http://www.bitsavers.org/pdf/practicalElectronics/digi-cal/
ReplyDeleteA calculator from the 70's, 100% ttl, now in PDF form.