Makevention 2015

Makevention went really well! I was able to show everything I have been working on, although I didn't have time to finish everything. I made a poster board explaining some concepts related to calculators like RPN, BCD, and CORDIC on the left side with information about my RPN Scientific Calculator on the right. I also had a print out of how my external RAM preprocessor works. A few of the people who came by my table were programmers and understood the solution.

On the table itself I had different calculators and projects laid out in roughly chronological order. The first was an MK-61 RPN calculator I added to my collection over 10 years ago. Of course I didn't make it but I wanted to show an example of an RPN calculator and what inspired me to first make calculators. When I first got the calculator out to test it, it didn't show anything on the screen and I was afraid it was broken. I took it completely apart and looked for burst capacitors. I also brushed off the battery contacts since they didn't look very clean. When I turned it on, it still didn't show anything but when I pressed a number it showed up! It seems the calculator just doesn't display anything when first turned on, instead of the zero I was expecting. Somehow I had forgotten that in the 10 years its been since I last used it.

The Casio Algebra FX 2.0 was included to show the RPN stack program I wrote for it in 2002 or so. That program was designed to make the calculator function more like the HP-48GX I had at the time which I admired so much. First, I had to buy a calculator to replace the Algebra FX 2.0+ I sold in college. Loading the program onto the calculator took quite a while to figure out! In 2002 I used a serial cable, which I think was an SB-87, to load programs without any trouble. Nowadays I don't have a serial port, so I bought an FA-124 USB cable. It turns out that this cable doesn't work on Windows 7. I also couldn't get it to work correctly under Windows XP running in an emulator. Next I tried a lot of different third-party software and finally got the program to load using FlashCOM 1.4v and an FTDI cable. For the link port I bought a 2.5mm plug that I could easily wire to the FTDI cable. After that, the program I loaded kept crashing and I thought the transfer was corrupt. After more fiddling I got Turbo C up and running in an emulator and compiled the program source myself, which produced a fairly stable program that was good enough for exhibiting, although it did crash a couple times during Makevention. Someday I would like to fix the program up and make it more stable.

The next thing I showed was a launchpad hooked up to a breadboard with a button and blinking LED to show how easy it is to get started with electronics. The next step was my binary LED calculator. I soldered a coin battery holder on to the board. After that I showed the RPN Scientific Calculator and explained that it was not too difficult to move to this stage after I managed to finish the binary LED calculator. The Programmable RPN Scientific Calculator was next. I printed temporary a colored keypad on poster paper which I taped to it, but it did not work very well. Unexpectedly, the calculator showed random keypresses when I put my hand near it. All the keys were in the same column on the keyboard, which makes me thing there is a bad connection in that row of the key matrix.

Next I showed the Improved 6502 Virtual Trainer up and running on my laptop, along with the first 6502 Virtual Trainer. I also showed what I had accomplished with the 6502 graphing calculator. So far, I have most of the hardware for it installed but I am having problems keeping the buffer chips for driving the LCD at the appropriate voltage level. Maybe the pins joining the sections of the calculator together aren't making a good connection. In any case, I showed the calculator taken apart into its sections. I also showed the Logic Tool I have been using to debug the graphing calculator and the EEPROM programmer I built. The last thing I showed was the TI-86 I bought to hook up to an ESP8266. My plan was to relay text from the calculator over WiFi to a computer running Matlab or similar software to allow the calculator to solve more complex equations. I still haven't gotten the ESP8266 voltage levels to work right, but I want to finish this project when I have time.

All in all it was a great day and I really enjoyed showing the public all the things I have been working
on.

New Project: Logic Tool

Since my plan to make a wireless breadboard did not work out, I decided to use the MCP23S17 shift registers I bought for it to make something similar. It is similar to a logic analyzer but shows information in real time rather than recording a short period of time at high resolution. It has female headers for 64 pins but so far I have only soldered 32 of them in. As time gets closer to Makevention, I'm trying to save time however I can to get my last few projects working.

With 64 pins I will have enough to monitor all of the lines of my 6502 project. Unlike a logic analyzer, I can

also switch any of the pins to be outputs. Now I am doing this with a simple GUI I made that shows or controls the lines with virtual LEDs. This saves me from hanging loads of LEDs on all the lines of my project. Later I would like to add other forms of input and output that I can drag and drop to the dark gray area in the middle of the form. This could include buttons, sliders or hex readouts like I had for my 6502 Virtual Project. At the moment, only the LEDs work and I am using them to drive the address and data lines of the 6502 socket for my graphing calculator project. This lets me check the control signals of the CPLD fairly quickly.

In the end I think this project will work out better than the plan I had for the Wireless Breadboard. When I tried the breadboard I was going to use with another project, it showed a big voltage drop across the rails. I did not know this could happen and it would have been unfortunate to build the whole project and then find out the board was not very good.