24 Oct
2002
24 Oct
'02
11:11 p.m.
At 03:49 PM 10/24/02 -0700, you wrote:
On Thu, 24 Oct 2002, no wrote:
That sportster needs 9VAC. Older sportsters need 12VAC.
I don't know about the Motorola.
carlos.
--------------------------------------------------------------
Carlos E. Murillo-Sanchez carlos_murillo(a)nospammers.ieee.org
I have a couple of (almost classic) external
modems missing
the wall warts. Anyone on list running either of these that
can provide the dc voltage/current requirements? Thanks.
Sportster 33.6 faxmodem
Motorola ModemSurfer 33.6
Dont know specifically about those (Though I did have the
Motorala
one years ago) but _many_ newwer modems run on 9 VAC adapters... 
25 Oct
25 Oct
6:31 p.m.
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9:47 p.m.
Tony Duell wrote:
Always thought that was rather clever
.
Two half-wave circuits with diodes conducting in opposite
cycles has to be the cheapest way to get bipolar supplies.
These days, it seems everyone's using MAX232s instead to get
the required negative supply. Which is good since the other
solution rules out battery ops. And everything cool is
goin'
portable. Look at the SX-64 :)
-- Ross
That sportster needs 9VAC. Older sportsters need
12VAC.
I don't know about the Motorola.
FWIW, the 'AC' is important. You can't use a DC-output adapter. Many
modems (and other devices with RS232 ports) produce both a +ve and -ve
supply from the AC input for the RS232 buffers (and maybe the analogue
circuitry too).
-tony 
26 Oct
26 Oct
10:01 a.m.
Ross Archer <archer(a)topnow.com> wrote:
Two half-wave circuits with diodes conducting in
opposite
cycles has to be the cheapest way to get bipolar supplies.
Unless you have AC with a center tap, how is "two half-wave
circuites with diodes conducting in opposite cycles" different
than one full-wave rectifier? Maybe I don't understand how
your suggesting it would be wired? Perhaps some ASCII art
would help. (Doesn't have to be fancy.)
Thanks,
Eric
10:27 a.m.
On Sat, 26 Oct 2002, Eric Smith wrote:
Ross Archer <archer(a)topnow.com> wrote:
lead 1 of transformer is ground,
lead 2 of tranformer goes to anode of diode A and cathode of diode B
+ 1/2 wave power comes from cathode of diode A
- 1/2 wave power comes from anode of diode B
The diodes conduct on opposite cycles (like a full wave centertap supply) but
in this case one diode generates the + supply and the other generates the -
supply...
Peter Wallace
Two half-wave circuits with diodes conducting in
opposite
cycles has to be the cheapest way to get bipolar supplies.
Unless you have AC with a center tap, how is "two half-wave
circuites with diodes conducting in opposite cycles" different
than one full-wave rectifier? Maybe I don't understand how
your suggesting it would be wired? Perhaps some ASCII art
would help. (Doesn't have to be fancy.)
Thanks,
Eric
1:13 p.m.
Peter Wallace wrote:
lead 1 of transformer is ground,
lead 2 of tranformer goes to anode of diode A and cathode of diode B +
1/2 wave power comes from cathode of diode A
- 1/2 wave power comes from anode of diode B
The diodes conduct on opposite cycles (like a full wave centertap
supply) but in this case one diode generates the + supply and the other
generates the - supply...
Thanks, I think I understand now.
Why are you on the list instead of down here at the Vintage Computer
Festival? :-)
(Actually I'm not there yet myself. I'm waiting for the color printer
at work to disgorge a few more pages, then I'll head over.)
1:42 p.m.
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2:39 p.m.
Very... The only full-wave rectifier you can get
without a centre-tapped
input is a bridge, and that doesn't have a common connection between
input and output for one thing. It also only gives a single polarity
output.
...
Basically 2 half-wave rectifiers, each accepting one
half of the AC input
There is a useful way to use a bridge to do this. It wastes half of it,
but it's a single component that doesn't need its leads formed instead of
two that do, so I often use it. Probably not cost effective for mass
production, though.
+--------+
| |
-----| ~ + |-------+---------------- +V
| | |
--*--| ~ - |-------(----+----------- -V
| | | _|_+ _|_-
| +--------+ ___ ___
| | - | +
+-------------------+----+----------- gnd
3:01 p.m.
It should be stated (and obvious) that you can ONLY safely do this with a
transformer coupled supply. Otherwise you potentially have the classic "hot
chassis" condition. And be sure to consider the effect on things if you
were to build a device that had a serial connection or somesuch powered off
the same transformer.
This technique works fine, but is not without peril if you don't fully
understand what you're doing.
--John
-----Original Message-----
From: cctalk-admin(a)classiccmp.org [mailto:cctalk-admin@classiccmp.org]On
Behalf Of Jim Kearney
Sent: Saturday, October 26, 2002 15:41
To: cctalk(a)classiccmp.org
Subject: Re: modem help
Very... The only full-wave rectifier you can get
without a centre-tapped
input is a bridge, and that doesn't have a common connection between
input and output for one thing. It also only gives a single polarity
output.
...
Basically 2 half-wave rectifiers, each accepting one
half of the AC input
There is a useful way to use a bridge to do this. It wastes half of it,
but it's a single component that doesn't need its leads formed instead of
two that do, so I often use it. Probably not cost effective for mass
production, though.
+--------+
| |
-----| ~ + |-------+---------------- +V
| | |
--*--| ~ - |-------(----+----------- -V
| | | _|_+ _|_-
| +--------+ ___ ___
| | - | +
+-------------------+----+----------- gnd
4:07 p.m.
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10:05 p.m.
Two AC generators with opposed phase being run from the same drive shaft.
Peace... Sridhar
On Sat, 26 Oct 2002, Eric Smith wrote:
Ross Archer <archer(a)topnow.com> wrote:
Two half-wave circuits with diodes conducting in
opposite
cycles has to be the cheapest way to get bipolar supplies.
Unless you have AC with a center tap, how is "two half-wave
circuites with diodes conducting in opposite cycles" different
than one full-wave rectifier? Maybe I don't understand how
your suggesting it would be wired? Perhaps some ASCII art
would help. (Doesn't have to be fancy.)
Thanks,
Eric
1:35 p.m.
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6:37 p.m.
At 06:54 PM 10/26/02 +0100, you wrote:
One of the most annoying instances of this is the
HP82164 HPIL-RS232
interface. It runs off the standard HP 8V transformer (AC output).
-snip-
This means, of course that you _must_ use an AC input
for this device.
Which makes it next to impossible to run off batteries. A pity, since
having a portable HPIL-RS232 interface would be useful sometimes.
Yes. I have a clone of the HP82164 made by Handheld Products which
is totally portable, with internal NiCd batteries. Even the form
factor is identical. Unfortunately, it is not working right now, as
the batteries spilled and the spill ate some traces. I'll have to get
to fixing it some time...
carlos.
--------------------------------------------------------------
Carlos E. Murillo-Sanchez carlos_murillo(a)nospammers.ieee.org
27 Oct
27 Oct
5:30 p.m.
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8104
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13 comments
8 participants
participants (8)
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archer＠topnow.com -
ard＠p850ug1.demon.co.uk -
carlos_murillo＠epm.net.co -
eric＠brouhaha.com -
jcwren＠jcwren.com -
jim＠jkearney.com -
pcw＠mesanet.com -
vance＠neurotica.com