Tuesday, September 14, 2010

8085 Computer Power Management

I'm in the final stages of hardware work on my 8085 computer project. Today I spent some time working on reducing how much power it uses.

8085 computer project during power use measurement and testing.
The MAG-85 still looks like a rats nest here. I pulled out a bunch of parts for today's testing. It'll go back together again even better.

With all peripherals turned on at full power, some of them at a higher level than would be normal or reasonable, the whole thing pulled 720mA at 5V. At full reasonable power levels, everything on, it came down to about 250mA. I put in current limiting to cap it at that level.

Then I went hunting for further power savings. The plan is to run this thing off of batteries in the not too distant future (I normally run it off an AC adapter now.) By seeing how little power I could feed to the LEDs in the system while still having them visible in bright light, I was able to cut overall power use down to about 160mA with everything on. It draws about 125mA with the LCD display on, the system running full bore, but no extra outputs pulling current. I can live with that.

What surprised me the most was that changing the CPU from an 8085AH microprocessor to an 80C85 (CMOS, low power version) didn't make any significant difference to the amount of power the system required. The LEDs accounted for almost all of the decrease from 720mA to 125mA.

8085 computer enclosure being sniffed by our cat.
The enclosure during inspection by Quality Control. The first attempt is on the left, the final version on the right.

I'm very close to closing this box up and calling it done. At least until I open it up for further upgrades. Upgrades like full 64K memory decode, an additional 8K of memory on board, and an RS-232 serial port. Later.

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