So I built an SDrive-MAX Arduino powered device but have a problem when it's wired up as expected, with an 1N4148 diode connected between the Atari DATA IN line and the Arduino TxD pin. I removed the diode and voila, it works again. I asked about this a few days ago in another thread:
Cathode (black band) end soldered to the Arduino.
Which confirmed what I had done. Anyway, to avoid cluttering up that thread (which is about ATX support being added to the SDrive-MAX firmware), I decided a new thread would be more appropriate, and probably helpful for anyone assembling these going forward. So ...
Anyway, I got my 3D-printed case today (huzzah!) and when I went to rewire the device with the diode installed again, I did it this way:
(After soldering, of course I trimmed off the excess leg and then covered everything with heat shrink).
I then soldered in the leg on the black band-side to the Arduino, and measured the forward bias of the diode (red probe of the multimeter in Pin 3 of the SIO plug, black probe on the pin of the Arduino) and got 0.601 volts, exactly as expected for a silicon diode. Reverse bias was OL measured by reversing the probes, also as expected. I put the device inside the case, booted the computer and … nada. So I took things apart again and soon as I removed the diode, things are working great again. Huh.
So variables: the type of Arduino used - a cheapie little clone Uno with additional vias inboard of the headers; power source: Atari SIO +5V pin. Makes no difference whether I plug it in directly to the computer or at the end of the daisy chain; computer used: 1088XEL, normally with an SIO2PC connection to RespeQt through a Sparkfun FTDI-based serial board, two 1050's connected to the SIO port, and a P:R:Connection at the end. I have zero problems using both the SIO2PC device or the floppy drives, simultaneously or separately. They just work. Of course, the XEL is designed for this and the Sparkfun FTDI board has the right isolation already for simultaneous work.
So does anyone have ideas why installing the recommended diode is interfering with my other SIO storage devices? I have not tested with another computer, though I'm tempted to this weekend to see if this is a quirk of the 1088XEL.
But in happier news, the thing works GREAT. My friend is still dialing in his printer so there are few imperfections but most of those will be easy to take care of this weekend with some very fine sandpaper. I stuck rubber feet on the bottom for stability too, which is highly recommended.