Re: [Kinda OT] Power Supply

[salfter@salfter.diespammersdie.dyndns.org (Scott Alfter)]

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In article <ce9c44dd.0408170659.516c726b@posting.google.com>,
Ralph Glatt <julian814@hotmail.com> wrote:
>The ZX81 takes a power supply that puts out 9v DC around 800 mA. I
>needed one, and a friend gave me a 9v AC power supply and said use
>that. Thing is, I'm afraid if I use the wrong kind of voltage, I might
>fry the board, which I don't want to do, because the ZX81 isn't all
>that easy to get in the US. Should I try it, or should I keep looking
>for a DC power supply?

Given the minimalist nature of the ZX81's design, feeding it AC when it
wants DC would probably toast it.  It'd be easy enough to lash up a bridge
rectifier, filter capacitor, and linear regulator to get regulated 9V DC for
your computer.  I think you can even still find all the parts at Radio
Shack.  For the rectifier, pick something that can handle around 1-1.5A. 
You could also use a diode instead of a bridge rectifier, but it won't be as
efficient.  For the capacitor, I'd pick 470 or 1000 uF at at least 25V.  For
the regulator, use an LM7809 in a TO-220 case; they're good for 1A.  You
might also want to bolt a heatsink to the regulator, as it'll get toasty
without it.

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