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EnigmA Amiga Run 1996 February
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EnigmA AMIGA RUN 04 (1996)(G.R. Edizioni)(IT)[!][issue 1996-02][Skylink CD III].iso
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hardware
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modempwr.lha
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ModemPower
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ModemPower.doc
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1995-12-17
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7KB
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194 lines
MODEMPOWER
... or how ç00l people say it
M0ðemPoWa!
;-----------------
SECTION Deny_all,DATA
I WON'T ACCEPT ANY RESPONSIBILITY ABOUT DAMAGES CAUSED BY USING OR MISUSING
THIS INFORMATION. YOU DO IT ALL AT YOUR OWN RISK.
Actually, this (as all of my hardware projects) includes only the idea of
the circuit. They're for people who do have some EXPERIENCE of constructing
;-----------------
SECTION What,DATA
So, whatta h*ll is this that you, on your weak moment, happened to download?
Maybe I'll tell a story...
Once upon a time :) there was a hacker. He was going to study in Oulu
Institute of Technology. He knew, that he was going to get his internet access.
So, he bought a modem, an external one, because he had no card slots in his
beloved computer. But, with the modem came also evil AC/AC-adaptor, that made
noises, mostly at the night. Bzzzzzzzzzzzzzzzzzzzzzzzzzzz.... all night long.
Hacker was unhappy. He was tired every morning after being awake all night
because of that evil AC/AC-adaptor. He got p*zzed off. One day, after eating
a delicious, plenty of vitamins containing meal at his school's cafeteria
(actually the food makes people having hallucinations :), he had an idea!
He has a 200 watts power supply in his computer! Plenty of power to get a
single modem running.
So, he tried to create a circuit, that converts +12V into 12VAC. He deliberated
upon it... night after day, day after night... until he discovered that a
power-audio-IC could be used as oscillator and charge pump for -12V! He made
first trial circuit based on a TDA2030 power IC. ... and it didn't work. IC
either oscillated at about 200kHz or didn't oscillate at all. Poor little guy
went to bed... sad... sooo sad.
Next day he began thinking the circuit over. This time he put, not two, but
three RC-timebases to feedback loop of the IC. It worked! It oscillated
promptly at 50 Hz, output being nice square wave. Eagerly he continued
building the charge pump and ±12V switching circuits. Later that night circuit
was just waiting for a test. During the test, however, become quite clear,
that the IC couldn't deliver enough voltage during +12V phase. So, the poor
little guy went to bed... sad... but not SO sad.
Next day he was thinking about ways to make the circuit capable of delivering
more voltage, and if possibe, current. Like a thunderbolt, idea of putting
a PNP transistor to connect original +12V to output instead of drawing it
from the IC stroke his mind. He put the transistor in and... Yes! +12V at
output was steady as rock, no matter how difficult load was connected.
After making some optimizing and further tests he connected ß-version of
the circuit to his computer and modem and went for a little ride into the
Internet....
Next day he made a little metal case for the circuit, reconstructed
the circuit into the case and connected it in. After testing it to work he
pulled out the BUZZZZZZZZZZZZZZZZZZing AC/AC-adaptor and abandoned it to
a dark, cold corner of his cupboard and lived happily ever after.
Hmm....
khm....
well.....
OK! OK! That 'poor little guy' is ME!
Yes! That AC/AC-adaptor BUZZZZing all night p*zzed me off!
Yes! I DO have a 200 watts PC power supply in my Amiga!
Yes! It took me some time to get this hack working!
Yes! It's working right now... in fact, I uploaded this package to Aminet using
my modem powered by MoDeMpOwA.
;--------------
SECTION More_Serious_Text,DATA
So? How does this.. thing work?
<picture: ModemPower.pic1>
Main component is, indeed, an audio-power-IC TDA2030. Its positive input is
connected to half of input voltage. Negative input is connected to output
via three phase-shifting RC timebases. When +12V is supplied to pin 5 of
the IC, pin 1 (+ input) raises to +6V. Positive input is higher than negative,
so, output will go high, to nearly +12V. From output current flows via 100k
resistors to 100n capacitors. First capacitor takes a little while to charge,
when it's charged, current flows thru second resistor to second cap and
finally thru third resistor to third cap and to negative input of the IC.
Negative input raises higher than positive input, so, output will go low,
nearly to 0V. Negative input follows it after a while, and so on.
<picture: ModemPower.pic2>
Square wave in output pin of the IC will be fed into charge pump, that is
2200/16V electrolytic capacitor and 1N4001 diode. When square wave goes up,
diode keeps cathode of the elco below 1 volt. About ten volts is charged into
the elco. When square wave goes down, cathode of elco goes down to about -9V,
that is connected to output of circuit via Q2. That happens, when square wave
is low. When it's high, Q3 gets it base current and draws base current from
Q1, that connects original +12V to output. At the same time, Q4 gets its base
current and supplies base current for Q5, that prevents Q2 from leading.
A 47n capacitor from output to ground is for suppressing RF disturbance.
;------------------------------
SECTION Before_Building,DATA
First! Make sure that your modem has either one of its power connector's pins
connected to GROUND of modem's RS-232/eqv. connector. That is vital, because
this circuit relies upon that. Otherways, some smoke will be generated.
I'm using this ...thing with my Well XM-2814SAM external modem. It seems to
work fine. I tested MoDeMPoWa with 1A positive half-wave load and 150mA
negative half-wave load. Worked fine. I tested powered my modem by MoDeMPoWa
and lowered input voltage. Problems occured when input voltage was as low as
8 volts. So, it seems to be enough headroom there...
About constructing the circuit.. do it as you like. It's wise to add a 1.25A
fuse to supply line of this circuit, in case something goes wrong (accidental
short-circuit between output and ground, that's quite possible).
Custom-made PCB would be nice, but a piece of vero board will do just fine.
Those power transistors won't need any cooling, they are just switches. The IC
needs a little cooling to prevent IRCing to stop because of overheating.
If the circuit is placed to a metal case, just attach the IC to the case.
IC's metallic part is connected to pin 3, that is, the ground.
You do remember to connect GND of ModeMpOwA to the ground-connected pin in
power connector of the modem, don't you? Otherways, the fuse recommended
earlier comes in handy.
Well, I think that's enough guidelines for you to construct the .. thing.
Long live and prosper, sano savolaenen.
Send snails to:
Arto Niskanen
Valtatie 8A8
90500 OULU
..and that's in FINLAND
..and electrones to:
archy@rhea.otol.fi
;----------------
SECTION ADDENDUM,DATA
<picture: ModemPower.pic3>
Just added some information about creating a -8VDC voltage with this... thing.
Might be CøøL for those tower-builders.. as nowadays seems that PeaSea-
Power'supplies' don't output any negative voltages. To make an Amiga work
with that kind of... PeaSeaCr*p'Power', use e.g. this to make serial port(s)
and audio output to work.
Principle is simple, a diode is used to grab that -9V part of a square wave
and an elco to filter it... This might supply a few hundred milliamps.
Nzoi!
17.12.1995 Archy