Date: Mon, 27 Mar 2000 17:11:26 -0800
From: Mark Willis <[EMAIL PROTECTED]>
Subject: Modem power considerations etc.
A while back, there was a post about modems and AC vs. DC power packs.
Usually designers use a Maxim MAX232 or equivalent - that chip creates
several needed voltages easily from the existing DC supply voltage,
using switched capacitors, and translates TTL levels to RS-232 levels.
Several other co's make that IC, as well. AC power packs are a little
cheaper to make - you then have to put the same rectifier/capacitor
parts inside the modem, instead of in the power pack, so it's just a
costs trade-off thing. Which power pack can you get cheaper and
reliably sourced, usually <G>
COST of device components is probably THE major consideration in most
consumer electronics - obviously, from watching the market, reliability
/ functionality come in second, fairly often =)
RS-232 usually hangs out at some negative voltage between -5 and -12V,
and goes positive when characters are sent; Details on the MAX232
family at http://dbserv.maxim-ic.com/quick_view2.cfm?pdf_num=1798, you
can grab a data sheet from there.
(I've been catching up on things, busier than I'd like!)
Mark
--
I re-ship for small US & overseas businesses, world-wide.
(For private individuals at cost; ask.)
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