Thanks for your suggestions, Kerem.
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1. I am resolving the S8 problem by changing Q3 from an FJN3305 (internal 4.7k) to an FJN3304 (internal 47k). If anyone wants an FNJ3304, email me and I can send you one for free.
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2. The piezo's beeps are indeed pretty weak. There simply was no room for anything better! That's why it's sitting on top of the ICs. However, a "naked" piezo doesn't make much noise. Some kind of speaker enclosure is needed to amplify the tiny movements of the disk into larger air movements. This usually take the form of a coin-shaped lid with a small hole in the center. For example, the lid of a pill bottle about the same diameter as the piezo disk, with a 1/8" hole in the center. That helps a lot (but adds height so it won't fit in an Altoids tin).
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A bigger or better speaker would be great. But where would I put it?
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3. I standardized on the white Molex KK series connectors because they are available with gold contacts, and have good spring pressure to make reliable?connections. The black "Arduino" style connectors that have become popular are cheap, but not very reliable. If you pull out a pin and look at the actual contact surfaces, you'll see that they are rough, and only tin plated or gold-flashed which wears off quickly, and there is no spring pressure to maintain contact pressure.
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But the Arduino-style connectors certainly make assembly easier. They are actually needed for the Z80-SIO card because the Molex KK connector would hit the 5v regulator.
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I'm thinking about removing the 5v regulator, as I doubt anyone powers their Z80MC with anything other than a 5v supply. This makes room for Molex connectors at all P1 and P2 locations on the CPU card. It also makes room to include the P4 power/serial connector on all CPU cards.
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4. Supporting NVRAM on the Z80-SIO card is a great idea! I'm not working on it at the moment, but will add it to my list of "things to do" when I order more PCBs. You could use a NVARM with built-in battery now; but they are expensive. Most likely, I'd use VIN (JP2 pin 20) to connect an external battery.
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5. Yes, there is room in the ROM to include some self-test capability. Another project! :-)
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Anyone have any other ideas?
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Lee
Lee Hart