Virtual Assistant - Index

Virtual Assistant — Index

This page collects my my posts on building a Virtual Assistant for my own personal use and its development.

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6502 - Part 2 Reset and Clock Circuit

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6502 Retro Console Part 2 Add a Reset and Clock Circuit In Part 1 we powered up the 6502 and watched it running a NOP test with just the CPU and LEDs on the address bus. Now we’ll give it a clock and a clean start every time you power on, rather than relying on a function generator. In this post we will cover a simple 555 Timer Clock circuit and reset circuit. 555 Timer The 6502 needs a steady pulse on its Φ0 (pin 37) to step through instructions. A NE555 timer is perfect for low-speed testing reliable, simple, and easy to wire. Parts List NE555 timer 1 kΩ resistor 10 kΩ resistor 100 nF capacitor (timing) 0.1 µF capacitor (decoupling) Breadboard + jumper wires Circuit Diagram How to Wire It Add a 0.1 µF decoupling cap across the +5V and GND rails stability. Typical speed: ≈ 7–10 kHz perfect for a visible NOP test. Use larger resistors or capacitors to slow it down. Tip: Swap the timing capacitor for 1 µF and the 10 kΩ for 100 kΩ to step slowly enough ...
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BBC Model B + MMFS: Command Guide

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BBC Model B + MMFS: Complete Command Guide for SD Card Systems If you’ve upgraded your BBC Model B with the MMFS SD-card interface , you’ve opened up a whole new way to use your retro computer. No more fragile floppy disks MMFS lets you browse, load, and run hundreds of disk images (.SSD or .MMB) straight from an SD card. This guide collects every useful command you’ll need to explore, manage, and boot software quickly on your setup. Quick Start — Create & Use Your Own MMFS Disk Here’s a simple first project to prove everything’s working. Goal: Create a blank disk, format it, write a BASIC program that prints “Hello, World!”, save it, and run it again. You can watch my YouTube video below and see the guides below for more commands. Create or Select a Blank Disk Slot Insert your SD card and power on. To check what’s available: *DCAT Then choose an empty slot (for example, disk 100): *DIN 0 100 This mounts disk 100 into drive 0 (your working drive). Format the Disk ...
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Math Behind Logic Gates

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Understanding the Real Electronics Behind Logic Gates (The Practical Math Behind Digital Circuits) When we build circuits with logic chips like the 74LS series, it’s easy to think only in 1s and 0s. But under the hood, every logic gate follows the same rules as any other circuit, Ohm’s Law, current limits, and voltage thresholds. So yes, there is real-world math behind those blinking LEDs and logic tables.  1. Logic Levels — The Digital View At the logic level, everything is simple: 0 V → LOW (logic 0) 5 V → HIGH (logic 1) We don’t care about exact voltages here just whether a signal crosses a defined threshold. For TTL (Transistor-Transistor Logic) chips like the 74LS86 XOR gate , these thresholds are: This means a logic gate “decides” based on whether the voltage is above or below that boundary, which is how binary logic becomes real voltage levels. 2. Inside the Circuit — Real Electrical Math Even though logic circuits process bits, they still obey Ohm’s Law ...
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