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'+5v from a PC parallel port'
1999\01\22@135631 by Adam Bryant

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Is it possible to get enough current from a PC parallel port to power a PIC
project.  I am building a DSO adapter for my PC that uses a 16C84, two
MAX187 ADC's, and a 741 quad op-amp.  Can a parallel port supply this much
current?  Or would I be better off including a 9 volt battery and a
regulator?

Thanks,
Adam

1999\01\22@144417 by Mark Willis

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Definitely can run at least just the PIC, it helps if your drivers
hold as many bits high at all times as possible, multiple ground pins
are a good idea, and I'd use Schottky diodes if you can to maximize
Vcc.  (Haven't used this on a PIC, but I have done enough protos with
Motorola processors that were powered this way to sink a small rowboat.)

 I'd guess that you're going to probably over-do it with the ADC's and
the 741, though;  You could tap the Keyboard connector for power, so
long as you keep initial surge current somewhat reasonable.

 (This is probably FAQ fodder, folks;  I could measure a current, and a
voltage, based on how I'd run the parallel port driver, or someone else
could, if we had numbers for how to power PC-attached projects like
"Keyboard port can supply 120 mA at 5V, Parallel port set up this way
can supply 20 mA at 4.5V" etc. in the FAQ, it'd be good for all of us, I
just don't remember what the parallel port numbers were last I had them
written down.)

 Mark

Adam Bryant wrote:
>
> Is it possible to get enough current from a PC parallel port to power a PIC
> project.  I am building a DSO adapter for my PC that uses a 16C84, two
> MAX187 ADC's, and a 741 quad op-amp.  Can a parallel port supply this much
> current?  Or would I be better off including a 9 volt battery and a
> regulator?
>
> Thanks,
> Adam

1999\01\22@152313 by myke predko

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Hi Adam,

It depends on the Parallel port.  On my PC at home, I have two parallel
ports.  one is an old ISA Adapter with only one parallel port (non EPP/ECP -
originally) I've had since Moses was a pup and consists of just discrete
logic and it could drive a battleship.

The other is the "SuperIO" parallel port that is built into the motherboard.
It can only source 1.2-1.5 mA per pin.  I have driven a 12C508 (which
requires 2 mA running at 4 MHz using the internal oscillator) from this port
by using the "-SLCT IN" and "-AUTO FD XT" connected through diodes (to
prevent backdriving).
Depending on the port, you could run your circuit from the parallel port,
but if you are thinking of running all those devices from a "SuperIO"
parallel port interface, you better look at using external power.

myke

{Quote hidden}

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1999\01\22@154108 by Adam Bryant

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Mark,
Thanks for the info.  I hadn't thought of the keyboard connector as a
potential source of power.  I had thought of hacking apart a spare power
connector inside the PC and running the lines outside, but discarded this
idea as I would like to be able to connect the DSO adapter to any PC and
run it without modifications.  I will probably go with the 9 volt battery
and a regulator.

I agree that a FAQ list would be a valuable resource.  Perhaps someone will
volunteer to host this FAQ on their web-site?  (I would, but I don't have
one yet).


Mark Willis wrote --->




spam_OUTmwillisTakeThisOuTspamNWLINK.COM on 01/22/99 12:41:26 PM

Please respond to .....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU

To:   PICLISTspamKILLspamMITVMA.MIT.EDU
cc:    (bcc: Adam Bryant/PEAK/MOORE)
Subject:  Re: +5v from a PC parallel port




Definitely can run at least just the PIC, it helps if your drivers
hold as many bits high at all times as possible, multiple ground pins
are a good idea, and I'd use Schottky diodes if you can to maximize
Vcc.  (Haven't used this on a PIC, but I have done enough protos with
Motorola processors that were powered this way to sink a small rowboat.)
 I'd guess that you're going to probably over-do it with the ADC's and
the 741, though;  You could tap the Keyboard connector for power, so
long as you keep initial surge current somewhat reasonable.
 (This is probably FAQ fodder, folks;  I could measure a current, and a
voltage, based on how I'd run the parallel port driver, or someone else
could, if we had numbers for how to power PC-attached projects like
"Keyboard port can supply 120 mA at 5V, Parallel port set up this way
can supply 20 mA at 4.5V" etc. in the FAQ, it'd be good for all of us, I
just don't remember what the parallel port numbers were last I had them
written down.)
 Mark
Adam Bryant wrote:
>
> Is it possible to get enough current from a PC parallel port to power a
PIC
> project.  I am building a DSO adapter for my PC that uses a 16C84, two
> MAX187 ADC's, and a 741 quad op-amp.  Can a parallel port supply this
much
> current?  Or would I be better off including a 9 volt battery and a
> regulator?
>
> Thanks,
> Adam

1999\01\22@182931 by Bob Drzyzgula

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On Fri, Jan 22, 1999 at 03:21:53PM -0500, myke predko wrote:
> Hi Adam,
>
> It depends on the Parallel port.  On my PC at home, I have two parallel
> ports.  one is an old ISA Adapter with only one parallel port (non EPP/ECP -
> originally) I've had since Moses was a pup and consists of just discrete
> logic and it could drive a battleship.
>
 ...

Could this then be rephrased "the current sourcing
capacity of this parallel port is limited by the
current sourcing capacity of the ISA bus"? And if
so, what is the +12V capacity of a typical ISA bus?
Thanks, just curious.

--Bob

--
============================================================
Bob Drzyzgula                             It's not a problem
.....bobKILLspamspam.....drzyzgula.org                until something bad happens
============================================================

1999\01\22@183135 by Bob Drzyzgula

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On Fri, Jan 22, 1999 at 06:18:39PM -0500, Bob Drzyzgula wrote:
>
> And if
> so, what is the +12V capacity of a typical ISA bus?
> Thanks, just curious.

Oops, I meant +5V. But that, too. :-)

--
============================================================
Bob Drzyzgula                             It's not a problem
EraseMEbobspam_OUTspamTakeThisOuTdrzyzgula.org                until something bad happens
============================================================

1999\01\22@204420 by Byron A Jeff

face picon face
>
> Is it possible to get enough current from a PC parallel port to power a PIC
> project.  I am building a DSO adapter for my PC that uses a 16C84, two
> MAX187 ADC's, and a 741 quad op-amp.  Can a parallel port supply this much
> current?  Or would I be better off including a 9 volt battery and a
> regulator?

The only way to get current is via the port output pins. There isn't much
there.

My current way of powering PC connected projects is via the keyboard connector.
I simply put two 5 pin DIN connectors on opposite sides of the project box,
wire the pins straight across, and pull +5 and ground into the project. Then
all you need to do is plug the keyboard in one connector, and a 5 pin DIN
cable in the other.

I used this to provide power to my homemade PIC programmer. Works like a
champ, and has had no ill effects on the keyboard (which I'm using to type
this message).

BAJ

1999\01\23@043556 by paulb

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Bob Drzyzgula wrote:

> Could this then be rephrased "the current sourcing capacity of this
> parallel port is limited by the current sourcing capacity of the ISA
> bus"?  And if so, what is the +5V capacity of a typical ISA bus?

 No, it couldn't (be thus rephrased).  The ISA bus is irrelevant to the
discussion.  Its capacity to deliver +5V is about 1 to 2 amps
continuous, similar for +12V, about ¸ amp each for -12V and -5V.

 This is unrelated to the parallel port which might just as well be
included on the motherboard (usually is nowadays) or a PCI card.  What
limits the parallel port is the chip attached, probably the most current
available from discrete TTL, less from the 82C11 series chips and least
from the multi-I/O and EPP/ ECP chips.

 The possibility of the current dropping off by virtue of certain
output configurations however, and brownouts muddling the PIC (remember
the thread?) is, at least to me, however off-putting.

 The keyboard conenctor is capable of an amp or so, but this involves
mucking about with unwieldy "T"-adaptors (called "wedges") and risks
upsetting the keyboard on this account.

 The Game port however, is a particularly serviceable means of sourcing
+5V as well as four direct inputs to the PC and one output.  There is of
course a tendency to leave it off recent PCs (well, how many people want
to use their PCs to play games?), mostly on the presumption that it is
now part of the sound card.  Ergo, current A-I-O boards usually *do*
have it as part of the sound card emulation.

http://www.hut.fi/Misc/Electronics/pc/interface.html

http://www.blackdown.org/~hwb/hwb.html mirrored at:
http://www.sonic.net/~alanwall/hwb/hwb.html
--
 Cheers,
       Paul B.

1999\01\25@120358 by Adam Bryant

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How well regulated is the +5v from using this method?  I would assume that
this is a pretty "clean" supply, but since my application will be using
ADC's I need a supply without a lot of ripples and what-not.  IIRC a
previous post stated that the keyboard +5v line could source 120ma.  Is
this correct?  I haven't calculated it all out, but my project should take
10-20ma max.

I really like this idea.  If the supply is clean enough I could make my DSO
adapter box with the aforementioned 5 pin DIN connectors and a 25 pin
connector for attaching a parallel cable and do away with the need for a 9v
battery and regulator.

Thanks,
Adam





byronspamspam_OUTCC.GATECH.EDU on 01/22/99 06:43:03 PM

Please respond to @spam@PICLISTKILLspamspamMITVMA.MIT.EDU

To:   KILLspamPICLISTKILLspamspamMITVMA.MIT.EDU
cc:    (bcc: Adam Bryant/PEAK/MOORE)
Subject:  Re: +5v from a PC parallel port




>
> Is it possible to get enough current from a PC parallel port to power a
PIC
> project.  I am building a DSO adapter for my PC that uses a 16C84, two
> MAX187 ADC's, and a 741 quad op-amp.  Can a parallel port supply this
much
> current?  Or would I be better off including a 9 volt battery and a
> regulator?
The only way to get current is via the port output pins. There isn't much
there.
My current way of powering PC connected projects is via the keyboard
connector.
I simply put two 5 pin DIN connectors on opposite sides of the project box,
wire the pins straight across, and pull +5 and ground into the project.
Then
all you need to do is plug the keyboard in one connector, and a 5 pin DIN
cable in the other.
I used this to provide power to my homemade PIC programmer. Works like a
champ, and has had no ill effects on the keyboard (which I'm using to type
this message).
BAJ

1999\01\25@121414 by John Payson

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|The other is the "SuperIO" parallel port that is built into the motherboard.
|It can only source 1.2-1.5 mA per pin.  I have driven a 12C508 (which
|requires 2 mA running at 4 MHz using the internal oscillator) from this port
|by using the "-SLCT IN" and "-AUTO FD XT" connected through diodes (to
|prevent backdriving).

I thought it was common for the non-data wires to be open-collector
with moderate pullips; using them for supplying power would seem
like it wouldn't be terribly effective.  Have you measured the data
pins?  Those should be beefier.

BTW, on the original PC printer port, all of the outputs except for
the eight data pins could be used as open-collector I/O pins, there-
by allowing full eight-bit transfer of data into the PIC.  Unfortun-
ately, Toshiba laptops (at least the ones I've seen) don't preserve
this ability.

1999\01\25@135839 by Byron A Jeff

face picon face
>
> How well regulated is the +5v from using this method?  I would assume that
> this is a pretty "clean" supply, but since my application will be using
> ADC's I need a supply without a lot of ripples and what-not.  IIRC a
> previous post stated that the keyboard +5v line could source 120ma.  Is
> this correct?  I haven't calculated it all out, but my project should take
> 10-20ma max.

The amperage is fine. I wouldn't dare comment on the noise though as it is
the main +5 supply for the PC. From what I've read there usually is quite
a bit of noise on that particular supply, which is shared with the buses and
the disks. Which is why folks have suggested regulating the 12V supply instead
of using the 5V. Best bet is to take a scope to a few different PC's and see
how it looks.

>
> I really like this idea.  If the supply is clean enough I could make my DSO
> adapter box with the aforementioned 5 pin DIN connectors and a 25 pin
> connector for attaching a parallel cable and do away with the need for a 9v
> battery and regulator.

That's the idea. However if it turns out that the line isn't clean enough
you can always resort to the hybrid method where you supply the ADC from a
battery generated, regulated supply and power the rest from the keyboard. I
did exactly this for my programmer because I needed 13V which I regulate down
from 2x9V batteries. The 5V helps out because I use a consistently powered
5V circuit to control the batteries to eliminate drainage when not it use.

BAJ

1999\01\25@140457 by Steve Blackmore

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On Mon, 25 Jan 1999 09:44:47 -0700, you wrote:

>How well regulated is the +5v from using this method?  I would assume that
>this is a pretty "clean" supply, but since my application will be using
>ADC's I need a supply without a lot of ripples and what-not.  IIRC a
>previous post stated that the keyboard +5v line could source 120ma.  Is
>this correct?  I haven't calculated it all out, but my project should take
>10-20ma max.

I haven't used parallel port, but have powered adc via serial port 5v
- seems to work fine on desktop machines but not on all laptops. The
supply, however is pretty clean.


Steve Blackmore
--
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Telephone 01744 752256          Mobile 0831 768478
Email: RemoveMEsteveTakeThisOuTspampilotltd.u-net.com  WWW: http://www.pilotltd.u-net.com

1999\01\25@152935 by myke predko

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Hi John,

>|The other is the "SuperIO" parallel port that is built into the motherboard.
>|It can only source 1.2-1.5 mA per pin.  I have driven a 12C508 (which
>|requires 2 mA running at 4 MHz using the internal oscillator) from this port
>|by using the "-SLCT IN" and "-AUTO FD XT" connected through diodes (to
>|prevent backdriving).
>
>I thought it was common for the non-data wires to be open-collector
>with moderate pullips; using them for supplying power would seem
>like it wouldn't be terribly effective.  Have you measured the data
>pins?  Those should be beefier.

I measured 1 mA for sinking and sourcing for this particular PC.  If they
are open-collector/open-drain, doesn't that still indicate that power would
have to be driven external to the card?

myke

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Now Available!  "Programming and Customizing the 8051 Microcontroller".
Find out more at:

http://www.myke.com/My_Books/pac8051.htm

1999\01\25@182336 by paulb

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Byron A Jeff wrote:

> The amperage is fine.

 120mA for the keyboard connector is nominal.  Except for rare machines
which are fused (like the NEC SX16 I just cleaned), it could deliver up
to 5 amps if you trusted the connector.  It is *limited* only by the
main SMPSU.  If you want 250mA for example, that is almost always
doable.  Similar for games port.

> I wouldn't dare comment on the noise though as it is the main +5
> supply for the PC.

 I'd reckon it pretty horrendous.

> Which is why folks have suggested regulating the 12V supply instead
> of using the 5V.

 But we were talking of externally available supplies.

> That's the idea. However if it turns out that the line isn't clean
> enough you can always resort to the hybrid method where you supply the
> ADC from a battery generated, regulated supply and power the rest from
> the keyboard.

 Batteries?  Ugh!  I hate batteries.  If sub-regulation to a 2.5V
reference is appropriate, that would be one option.  Otherwise a MAX-232
to generate 10V and regulate that back to 5 for the reference.  *DO*
pay attention to board design, lead dress and as was mentioned,
shielding if that helps.

> I did exactly this for my programmer because I needed 13V which I
> regulate down from 2x9V batteries.

 I hate batteries.  Worst of all for something you use only very
occasionally.  There is a chip called a TL497 which isn't particularly
expensive, used in most serious programmers.  Once you are used to using
it, no other way is worth doing (hint; voltage can be *programmed* using
a 74HC05).

Steve Blackmore wrote:

> I haven't used parallel port, but have powered adc via serial port 5v
> - seems to work fine on desktop machines but not on all laptops.

 Well, except for the laptops, the serial port can be regarded as a
current source from somewhat *greater* than 5V, to which you use a shunt
regulator, so it should work quite well for ADC.
--
 Cheers,
       Paul B.

1999\01\26@035013 by Dr. Imre Bartfai

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Hi,
I would rather say: no, can not supply. I made a dongle-like device, and
it worked reliable only if I took 16LF84. Newer paralel ports often
deliver only 3.3 V

Hope this helps.

Imre


On Fri, 22 Jan 1999, Adam Bryant wrote:

{Quote hidden}

1999\01\26@040727 by Jim Robertson

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At 09:40 26/01/99 +0100, you wrote:
>Hi,
>I would rather say: no, can not supply. I made a dongle-like device, and
>it worked reliable only if I took 16LF84. Newer paralel ports often
>deliver only 3.3 V
>
>Hope this helps.

Well it helped me. Thanks for the tip!

Jim

{Quote hidden}

--------------------------------------------------------
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Email: spamBeGonenewfoundspamBeGonespampipeline.com.au

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