A while back, I realized that the Z80 was drawing (relatively speaking) a lot of power. I know modern CPUs can both crunch your numbers and cook your dinner; the Intel Core i7 datasheet specifies a maximum of 145 AMPS of current. (I don’t think my car’s starter motor draws that much, some days.)
The Z80, though, being from the ancient glory days of yore when CPUs didn’t even require a heatsink, let alone sophisticated cryogenics, didn’t really strike me as a power hog. In fact, the version the DrACo/Z80 uses is CMOS-based (for static clockability) — it couldn’t be drawing some 700 milliamps of power all on its own, could it?
No, as it turns out. The Z80 itself is quite efficient. The 74LS245 buffer chips, on the other hand, draw 40 or 50 mA apiece, even when doing absolutely nothing. They just sit there and get warm! “Low-power Schottky,” my paleotechnological posterior!
A quick look online turned up the drop-in replacement 74HCT245 version, which is much more power-friendly. (These only draw a few microamps when idle.) The results speak for themselves…
Much more Earth-friendly! (…and now the computer can be run from a USB port or from NiMH batteries. Whether the Department of Security Theater would let me on a plane or on Amtrak with it is most likely another story, though.)
I’m also experimenting with removing the ’245 chips connecting the Z80 to the bus. It works well enough to do the Prime Number program, but may not be as stable for high-speed operation. More on this later (time permitting).