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borb / amigahid-pico

Use USB input devices on Amiga computers, using the excellent Raspberry Pi Pico as a USB-to-bitbang adapter.
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Simpler breadboard ciruit. #30

Open MrSVCD opened 10 months ago

MrSVCD commented 10 months ago

Hi I was looking for a way to simplify the circuit for building on a breadboard pcb. Specifically this: https://www.electrokit.com/en/product/experiment-board-breadboard-pcb-840-holes/ Can I use two 74HC/HCT/LS541 as level converter for a Amiga 500 or will this break the 500?

borb commented 10 months ago

I haven't used that particular part, but I can't see why not. The A500 has a lot of 74-series logic inside it. As with everything, always check any levels with a meter before attaching to the Amiga itself. I have heard that the RP2040 is pretty tolerant of greater than 3.3V levels but I can't confirm if it would tolerate it long term; some work has been done using it to drive the a floppy disk drive, and that's 5V active low.

My only word of warning is that the current drain on the KBRESET using some 5V level shifters (e.g. TI TXS parts) is substantial enough that the voltage drops below a level sufficient to prevent the Amiga from randomly resetting when the current drops. It could be fixed with a pullup resistor on the reset line but I opted to use mosfets instead.

The same drain is also present on the potentiometer inputs on the controller ports if you're hooking those up as well (middle mouse and right mouse inputs are pot inputs for analogue devices).

Definitely interested in hearing your findings; I'd really like to simplify the design and stop using the array of mosfets & resistors