--- layout: project title: Adventures with old calculators description: Shenanigans with graphing calculators my school was throwing away year: current permalink: /projects/calculators thumbnail_url: /assets/images/calculators.webp SEO_tags: [Calculator, Texas Instruments, TI82, Z80, Assembly, MS-DOS, Overclocking] --- **Note: This article is still expanding, check back later for more content!** In January 2023, my high school was getting rid of over a hundred old calculators. Around half were mismatched scientific and 4-function calculators, and the other half consisted of graphing calculators from the early and mid 1990s. Most of the graphing calculators are Texas Instruments TI-82, so this article will be focused on them, but I do plan on making other posts. After replacing the dead batteries every single TI-82 turned on and functioned, but some had malfunctioning screens. # Overclocking This section is based on [this archived webpage](https://web.archive.org/web/20220303160216/http://richfiles.solarbotics.net/Turbo82.html). There is a 26pf capacitor labeled **C7** on the top right of the TI-82's motherboard. When this is replaced with a 15pf capacitor, the speed of the calculator increases by 2-2.5x. Here is the resistor before and after replacement: Split photo of motherboard with old and new resistor And here is a speed comparison between a stock TI-82 (left), and an overclocked TI-82 (right): # Connecting to computer The TI-82 and TI-85 introduced the ability to connect to another calculator or to a computer to share programs. ## Hardware The TI-82 (and TI-85) used the TI Graph-link adapter, which connected to the calculator's link port and to a computer's 9 or 25-pin serial port. Luckily, this serial adapter can be converted to USB (shown below). Photo of TI-Graph Link adapter attached to a serial to USB adapter ## Software The TI-Graph Link™ software only supports very old versions of Microsoft Windows based on DOS, and some ancient versions of Mac OS. I chose to run the software in an MS-DOS virtual machine with Windows 3.1 since I already have experience with the platform. If you want to replicate my virtual machine, use the [MS-DOS 6.22](https://winworldpc.com/product/ms-dos/622) and [Windows 3.1](https://winworldpc.com/product/windows-3/31) images from WinWorldPC, and use this archive of the [TI Graph Link Software](https://archive.org/details/TiGraphLink). For transferring files I decided to use a physical Floppy Drive since I had one lying around. Here is my Proxmox configuration file (I would recommend editing the config file after creating a VM through Proxmox). ```yaml # Replace with your floppy drive block device args: -fda /dev/sdb acpi: 0 # You may need to enable booting from floppy to install DOS boot: order=ide0 cores: 1 cpu: kvm32 hotplug: disk # Change this to the storage device you want to store your OS ide0: local-lvm:vm-69420-disk-0,size=2G localtime: 0 memory: 512 name: msdos numa: 0 ostype: other scsihw: virtio-scsi-pci # Replace with your serial adapter serial0: /dev/ttyUSB0 sockets: 1 tablet: 1 tags: ms-dos vga: std ``` ## What's next Both CRASH and ASH allow you to create and load programs written in Z80 assembly. In the near future I plan on creating some basic programs in assembly and stretching the limits on what can be run on a TI-82.