Searching \ for 'Can I get +5v from serial Port ????' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: www.piclist.com/techref/io/serials.htm?key=serial
Search entire site for: 'Can I get +5v from serial Port ????'.

Truncated match.
PICList Thread
'Can I get +5v from serial Port ????'
1998\12\20@181922 by Ricardo Ponte G

flavicon
face
Hi Piclister:


       I need some support of you:


       I«m in the development of a prototype and one part of it is a data lin
k
via RS-485 from the work area to a PC (EIA-485 to RS-232) in an office.  

       I«d like to know if I it«s possible get the power (+5v) from the ser
ial
port of the Computer.  I do not want to use the typical parts of a power
supply (transformer, bridge and a capacitor) to make work this little
module of comunication.



       Thanks for your time.

1998\12\20@190459 by James Cameron

flavicon
face
part 0 1152 bytes
I have successfully derived sufficient power for small projects by
attaching a diode to DTR, RTS and TXD with the cathode of each attached
to the input of a 5V regulator.  Attached is a small schematic.

I'm not an expert in such things, though.

My electronics engineering friend says "It'll work - as long as they 1/
set the bits to the correct sense with software and 2/ don't take too
much current.  1n914 [diode] is enough for low current"

Serial ports vary.  Some drivers are high impedance and won't deliver
sufficient current.  I wouldn't want to make a product for sale without
testing it against a reasonable number of computers.

--
James Cameron                                      (spam_OUTcameronTakeThisOuTspamstl.dec.com)

OpenVMS, Linux, Firewalls, Software Engineering, CGI, HTTP, X, C, FORTH,
COBOL, BASIC, DCL, csh, bash, ksh, sh, Electronics, Microcontrollers,
Disability Engineering, Netrek, Bicycles, Pedant, Farming, Home Control,
Remote Area Power, Greek Scholar, Tenor Vocalist, Church Sound, Husband.

"Specialisation is for insects." -- Robert Heinlein.
Attachment converted: wonderland:parasitic.gif (GIFf/JVWR) (00022417)

1998\12\20@234325 by Mark Willis

flavicon
face
James Cameron wrote:
{Quote hidden}

 One company I worked with (contracted to do some stuff for them), sued
Microsoft for patent infringement on this, AFAIK they still have a
patent or copyright or the like on this, for personal projects no
problem, but for company stuff you could want to watch for infringements
here.  I don't know the outcome of that trial.  I could ask Jay or Don,
they'd remember <G>  IQ Technologies held the patent.  (Most things I
did with them were parallel port items, bugfixing, debugging, and
prototyping, as I took some *hard* classes.)

 Schottky diodes are good here as they lose less voltage (~0.4V vs.
0.7V.)  If that makes a difference, apparently it can sometimes.  Same
technique works on parallel ports (especially if you drive all the port
bits you can, high, as much of the time, both while idle & while
transferring data - that augments the power capacity of the parallel
port a bit, when needed.

 For serial ports, just make sure you have DTR (for example) held high
as much as possible, a very efficient & low dropout regulator as needed,
the more diodes conducting in parallel, the better!

 If you wire a custom cable, put +5 volts on a specific pin that's
normally unused, [and make sure not to plug it into anything that
doesn't expect that voltage!!], you can also use that (or run 9-12 volts
& regulate it on the other end.)  This IS considered REALLY cheating,
but can reduce re-cabling needs & save you.  (Saved ME having to rip
100' of concrete w/hand tools once, someone else messed up.  RS-232 over
a 150' cable, worked *surprisingly* well at 9600 baud.  They wanted to
add something sans AC power at the other end, fortunately 25-pin RS-232
cable, so extra ground & extra power pin {current loop pins, anyone?},
and WHEW!)

 Simple is good, anyways <G>

 Mark, mwillisspamKILLspamnwlink.com, too verbose here I guess...

1998\12\20@234333 by Ricardo Seixas

picon face
Hi Ricardo,

       Try Microchip AN555.


Ricardo Seixas

>Hi Piclister:
>
>        I need some support of you:
>
>
>        I«m in the development of a prototype and one part of it is a data
link
>via RS-485 from the work area to a PC (EIA-485 to RS-232) in an office.  
>
>        I«d like to know if I it«s possible get the power (+5v) from the
serial
>port of the Computer.  I do not want to use the typical parts of a power
>supply (transformer, bridge and a capacitor) to make work this little
>module of comunication.
>
>        Thanks for your time.
>
>

1998\12\21@064740 by Caisson

flavicon
face
> Van: Ricardo Ponte G <.....rniniverKILLspamspam.....CANTV.NET>
> Aan: EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU
> Onderwerp: Can I get +5v from serial Port ????
> Datum: zondag 20 december 1998 12:15
>
> Hi Piclister:

Hello Ricardo,

>         I need some support of you:
>
>         I«d like to know if I it«s possible get the power (+5v) from the
serial
> port of the Computer.  I do not want to use the typical parts of a power
> supply (transformer, bridge and a capacitor) to make work this little
> module of comunication.

It depends on the current you need.  Try a resistor,Zener-diode and a
capacitor (over the Zener).  That'll work for low currents ...

Greetz,
 Rudy Wieser

1998\12\21@101251 by Andy Kunz

flavicon
face
>>         I«d like to know if I it«s possible get the power (+5v) from the
>serial
>> port of the Computer.  I do not want to use the typical parts of a power
>> supply (transformer, bridge and a capacitor) to make work this little
>> module of comunication.

Maxim has an app-note which shows how to get power from the RXD pin
sufficient to run a PIC.  I forget which, but I've seen it several times
tehre.

Andy


==================================================================
Andy Kunz - Statistical Research, Inc. - Westfield, New Jersey USA
==================================================================

1998\12\21@172716 by paulb

flavicon
face
Mark Willis wrote:

>   Schottky diodes are good here as they lose less voltage (~0.4V vs.
> 0.7V.)  If that makes a difference, apparently it can sometimes.

>  For serial ports, just make sure you have DTR (for example) held high
> as much as possible, a very efficient & low dropout regulator as
> needed, the more diodes conducting in parallel, the better!

 The trick is, why use a regulator?  Parallel all the diodes, Schottky
if you're being critical, to the 5V rail and use a stiff Zener.  Two
aspects of this; RS-232 drivers are by definition current limited
(definition is, if they aren't, then they aren't RS-232 you see!) so
you don't need current limit resistors (you might add a small one).

 Secondly, you don't use an RS-232 receiver chip and you *certainly*
don't use a transmitter.  RXD is routed to the PIC via a limiting
resistor, but the diode "sucking" power from this line to power the chip
also limits this voltage to 5.6V.  A second diode or the appropriate DS
(Dallas) chip can actually "suck" negative voltage to use for the TXD
line, which otherwise uses the logic voltage direct from the PIC.

 Using a shunt regulator has the advantage that you get just that
little extra bit of current from the RS-232 line, though exactly how
much will depend on the individual port implementation.  You can get at
least 10mA however.
--
 Cheers,
       Paul B.

More... (looser matching)
- Last day of these posts
- In 1998 , 1999 only
- Today
- New search...