Tag Archives: Electronics

Building a PS/2 to 1351 Mouse Adapter

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I’ve been meaning to build myself a mouse adapter for the Commodore 64 for quite some time. The recent release of the unofficial port of “Eye of the Beholder” for the C64 was a welcome excuse to finally get to work on this project.

The Mouse 1351 made by Commodore can be plugged directly into the control port of the C64 or C128 and it has two different operating modes. In joystick mode, the input from the mouse is compatible with that of a regular, digital joystick. In proportional mode, which is the default, it behaves and feels like any mouse used on modern computers.

Commodore Mouse 1351. (Image source: Wikipedia, License: CC BY-SA 3.0)

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The KERNALquattro, yet another ROM Replacement

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Recently, I got hold of quite a few broken Commodore 64 motherboards. It has been a while since I last had the chance to repair one of those boards and it was fun! I dubbed this repair project the “Blank Screen Marathon” and documented the whole process in German on Forum64. I might still give a summary in English here at a later point. But today, I’d like to introduce a small side project that resulted from this repair marathon.

The 3 ROM chips on a C64 motherboard

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SyncFix64 Revisited – What about the VIC-20?

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It’s been over four years now that I created the SyncFix64 module in order to connect a cheapo car TFT display to my C64. This setup has served me well and it helped me repair quite a few motherboards since then. A few years later, when I got my first VIC-20 the display again failed to show anything despite the integrated SyncFix64 module. That was kind of disappointing, but I was lacking time and motivation back then to investigate further.

Composite video signal from a C64 as opposed to…

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Building a new ZX81 Computer

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The ZX81+38 is a clone of the Sinclair ZX81 home computer that replaces the ULA found in the original with standard logic ICs. That means, it can be built with all parts still readily available today. It was created by Mahjongg, introduced on a forum dedicated to Sinclair computers, and document on the web with construction files available on Github. 

The empty PCB as I received it.

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Pagefox – Reverse Engineered and Replicated

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Pagefox is a DTP (desktop publishing) software that comes as a cartridge for the expansion port of the Commodore 64. It was developed by Hans Haberl — who also created  the graphics editor Hi-Eddi and the word processor Printfox — and it was published and sold by the small German company Scanntronik which is actually still in business today.

Pagefox cartridge pried open

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ESD Protection for the C64 Control Ports

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The two 9-pin Control Ports located on the right-hand side of the C64 are used to connect joysticks and other input devices like paddles or even a mouse to the 8-bit computer. 

The two Control Ports.

The digital input pins are directly connected to one of the two 6526 Complex Interface Adapters (CIA) inside the C64, without any protection on the motherboard.

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Commodore VIC-20 S-Video Mod

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Last Summer, after a delay of mere 38 years, I finally acquired my first Commodore VIC-20, or VC 20 as it was called in Germany. Not all parts of the machine are in their original state as the connoisseur will notice on first sight. I don’t care too much about that because I didn’t want it as a collector’s item but as a technical gadget to play around with.

My first VIC-20, freshly supplied with a donor keyboard.

First thing I had to do to even test the machine was to make a new video cable to connect it to a monitor. The pin-out of the A/V jack differs from that of the C64: there is a Vcc output where the luminance signal should be and there is no S-Video output.

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Erasing and Programming the ATF1504 CPLD

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Last year, I acquired my first VIC-20 and when I discovered that someone shared the Gerber files for a fairly recent version of the Final Expansion 3 (english) for that machine on Github, I decided to set out and build one of those, of course. The FE3 might be a story for a later post, though. Because in order to build that cartridge, I first had to find an affordable way to program the ATF1504 CPLD that is used here.

The ATF1504 CPLDs turned out not to be not as “new” as the seller claimed.

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C64 Saver Evolution

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The original external power supply for the Commodore 64 comes in different forms but they all have one thing in common: With increasing age they are prone to failure and when they finally break they are likely to destroy the precious computer they were powering.

An original PSU for the Commodore 64.

The power brick for the Commodore delivers both 9V AC and 5V DC, the latter being produced from 9V AC with a voltage rectifier and a linear voltage regulator. While this voltage regulator is generally very reliable, it has to operate at the upper limit of its specification which takes its toll after decades of use. When the regulator finally breaks, it tends to short internally, thus supplying the sensitive TTL ICs inside the C64 with up to 9V instead of 5V since there is no integrated over-voltage protection.

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