Electrotopia⚡️

8-bit homebrew computers, analog electronics and 74-series madness!⚡️🪛

Original content from me and boosted content from the wider electronics community🔄

Living in the past but optimistic about the future.

Location: Cambridge🇬🇧
Career: Electronics engineer (consultant)
Fav programming language: Machine code
Born: This century

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tomcom_at_mastodon.nl@momostr.pink

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Last Notes

2026-07-11 18:43:16 UTC

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High praise indeed!

2026-07-11 18:20:24 UTC

I've been experimenting with interlacing on my new 8-bit video card and it's finally working!!!
https://mastodon.nl/system/media_attachments/files/116/902/721/525/650/472/original/6bdd0badcfc89718.jpg

2026-04-17 08:15:19 UTC

Fuck the first machine to pass the turing test. I wanna be the first human to fail it!
#AI

2026-04-11 11:40:06 UTC

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Well it never became a hit either. They sold less than 200.
But the hex editor was actually a step forward at the time. Contemporaries like the altar had front panels full of switches and lights by default. The hex editor did everything a front panel would, but did it in software. Quite cool I think!

2026-04-11 11:33:32 UTC

April 11th, 1976 - The #Apple 1 is released🍎
1MHz #6502, 4kB of DRAM (expandable to 8kB!), and a 40 by 24 character display.
#Woz was able to fit a simple hex editor in the limited 256 bytes of ROM in the machine, which allowed the user to enter, read, and run programs/data in RAM.
The schematic was interesting too. Woz had made his own TV typewriter terminal, similar to Don Lancaster's, and the Apple 1 was just a simple microcomputer bolted onto the front of it.
Happy 50th to the Apple 1🎉
https://mastodon.nl/system/media_attachments/files/116/385/784/760/767/272/original/17855aa6d761dfa3.jpg
https://mastodon.nl/system/media_attachments/files/116/385/777/717/985/115/original/9a6e98a936d71d3b.jpg
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2025-09-05 10:26:15 UTC

Anyone else ever notice that DIP-40 chips are never boring?
Like if you see a DIP-40 on a board, you know it's something interesting!
https://mastodon.nl/system/media_attachments/files/115/151/205/975/413/614/original/1acb074b063454e9.jpg

2025-07-01 21:48:28 UTC

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yep OG VGA textmode is 720 by 400...pretty cursed in my opinion. 9 horizontal bits per character🤮

2025-07-01 12:23:22 UTC

Three generations of keyboard interface cards for my Z80 machine.
First: Simple interrupt logic and two buffer ICs for reading X & Y signals from the keyboard matrix.
Second: Added connections and logic to also read two rotary encoders.
Third: Replaced the buffers with latches that are disabled when read (reduces chances of metastability) and reimplemented interrupt logic as a state machine.
Very happy with the final card. Represents a serious leap in engineering compared to my original.
https://mastodon.nl/system/media_attachments/files/114/777/913/259/123/586/original/90565de918ac3cea.jpg
https://mastodon.nl/system/media_attachments/files/114/777/913/767/886/053/original/a6122d9fd632a47f.jpg

2025-05-28 11:41:24 UTC

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decimal machines were pretty common in early computing. People weren't used to binary yet so lots of machines used BCD for arithmetic because it was easier for humans to understand and debug.
The extra hardware cost wasn't worth it though, so eventually pure binary machines prevailed.

2025-04-11 08:55:19 UTC

In 1981 #IBM got the legendary Paul Rand to redesign their logo. He did not disappoint.
Eye Bee M
https://mastodon.nl/system/media_attachments/files/114/318/484/474/095/730/original/eede614b43b4373b.jpg

2025-03-27 19:20:10 UTC

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it's just 640 with double wide pixels

2025-03-26 19:02:17 UTC

By designing the icons for the 1984 #macintosh, Susan Kare added a much needed personal touch to the computer industry.
Her icons were incredibly descriptive given they were just 32 × 32 pixels, and at that resolution she may also have been paid the most money-per-pixel of any digital artist in history! (I hear apple did pay her well)
Happy #marchinosh
https://mastodon.nl/system/media_attachments/files/114/230/216/763/118/447/original/ced36297f4cdf645.jpg
https://mastodon.nl/system/media_attachments/files/114/230/217/435/912/646/original/00c94d8a13bc73fa.jpg

2025-03-08 22:56:05 UTC

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oh I see. I just explained it badly.
The interrupt signal is generated by the ANDing them.
The CPU reads the raw inputs (through schmitt triggers)

2025-03-08 22:53:23 UTC

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when the first edge falls, the other with still be high and you're just looking at that to tell the direction.

2025-03-08 22:41:40 UTC

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thanks, I'll be writing drivers for it soon so this'll be useful.

2025-03-08 22:40:24 UTC

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all the inputs are active low, so I'm just ANDing them all together and the negative edge generates an interrupt.

2025-03-08 22:11:37 UTC

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https://en.m.wikipedia.org/wiki/Rotary_encoder
^ look at the section on incremental encoders.
The interrupt just causes it to store the outputs of the encoders (it's visible as an 8-bit input port), then schedule further processing the next time the OS is called.
The Z80 is running at 8MHz, pretty snappy, so the interrupt response time should be quick enough provided it's not serving lots of higher priority interrupts...but yes it is cutting it closer than I'd like.

2025-03-08 22:01:48 UTC

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and yeah the backup battery is a 9V.
I designed the buck converter to accept 9V from the wall anyway so this was another an easy addition.

2025-03-08 21:59:43 UTC

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no ADCs. They're rotary encoders so their output is digital.
All I'm doing is schmitt triggering the inputs and adding a bit of logic to generate an interrupt when it detects a low transition.
Most of the interrupt logic is shared with the keyboard anyway so this addition hasn't increased the chip count much.

2025-03-08 21:55:32 UTC

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thanks.
I was surprised about how easy it was. Everyone with an interest in electronics could (and should) apply for their foundation licence. It's only a couple of evenings of work.

2025-03-08 21:46:35 UTC

My #Z80 machine is getting some new input devices.
Watch this space!
#electronics #breadboard #homebrew
https://mastodon.nl/system/media_attachments/files/114/128/997/854/812/460/original/c793dac0d6204f81.jpg

2025-03-08 21:42:33 UTC

I've been meaning to get this done for a few years. So happy I finally found the time to do it!
🎙Callsign: M7TZC
#amateur #radio #foundation
https://mastodon.nl/system/media_attachments/files/114/128/974/073/774/469/original/0acae9a80a988f06.jpg

2025-02-06 23:00:44 UTC

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I'll take some of the MC34063s if they're still going?
It's a brilliant little chip!

2025-01-21 06:37:51 UTC

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i actually use a trick like this for my buffers.
If you put the buffer on a page boundary then you only need to reload the low half of the pointer (1 byte) as apposed to the full 16-bits.

2024-12-19 23:07:55 UTC

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yeah Set and Reset aren't synchronous. The output will change the moment you pull those inputs low, they don't use the clock.

2023-12-04 21:07:30 UTC

Finally got my 320 by 200 #VGA video card PCBs last week. Glad to be off the breadboard!
Here's a view of my hex editor on my #Z80 machine using it.
https://mastodon.nl/system/media_attachments/files/111/524/166/911/767/775/original/492c0e0dcb4a27c0.mp4