C64 Clock – Prototyping

Second Prototype

In the spirit of this site, this would probably be the final cartridge (pun intended).

Currently my successes on etching double sided PCBs are a little nonexistent. So I “quickly” milled a “few” slots in a raw PCB board with a Dremel. I did the rest using variboard.

The switches are all optional. I just can’t stop myself from adding “maybe eventually” – features. Except for the reset button, that’s quite useful.

Correction: If the switches are omitted, the address lines have to be grounded.

PDF Version of the schematic.

Unlike a 8kByte cartridge, a 16kByte type uses two control lines for two different memory areas (0x8000 – 0x9FFF and 0xA000 – 0xBFFF). To combine those two lines an AND gate is needed. I realized (i.e. half-assed) that using diode logic. The top side of the edge connector is partly soldered to the variboard utilizing capillary action to wick solder between the boards. Two connections had to be done with wires, though.

This is an AND gate.

First Cartridge Prototype

The first prototype board was too flimsy to handle the constant mounting and unmounting of the memory chip during development.

The original version of that prototype was for the 8k version of the software. I had a Textool socket for that EEPROM, but the new 128k EEPROM didn’t fit. Unfortunately, I don’t have a Textool socket for a 32pin chip, so I had to replace it with a regular socket which made reprogramming more annoying.

The reason I’m using a 128k EEPROM is because I’m an idiot who orderd the wrong chips and even ordered too many of them.

Mark 1