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