generation of 3.3v from COM port of a PC

[pmm]

Hello all
i want to power up a 3.3v IC which i want to place on the target
board.it is Connected to COM port of the PC is there any chance of
generating a 3.3v from the unused pins of the serial cord which is
connected to COM port of PC .(only three pins are used by me
presently those are 2,3,5)tranx ,receiv and GND)
If any body of you can help me with it i will be thankful
Regards
PMM

 

[Roger Hamlett]

"pmm" <muralipmanohar@hotmail.com> wrote in message
news:1f1fe31f.0403290240.3836135e@posting.google.com...

Hello all
i want to power up a 3.3v IC which i want to place on the target
board.it is Connected to COM port of the PC is there any chance of
generating a 3.3v from the unused pins of the serial cord which is
connected to COM port of PC .(only three pins are used by me
presently those are 2,3,5)tranx ,receiv and GND)
If any body of you can help me with it i will be thankful
Regards
PMM
The first question is how much current you need?. The second question, is

whether this is only ever going to connect to 'desktop' PC's, or might be
used with a laptop?. The third question is what software will be controlling
the serial port?.
Yes, you can use a small switching regulator to give 3.3v, with good
efficiency from the handshake lines. You can 'wire OR' the available lines
with diodes to increase the available current. There are a series of
problems though. The 'active' state for RS232, is a -ve output voltage.
Hence you either need to control the lines yourself, and take them to the
inactive state, or design the converter to include a voltage inverter (like
the little Maxim switched capacitor inverter). Quite a lot of laptops,
'stretch' the RS232 specification, and only run the bus at 5v. This reduces
the total power available.
A supply offering just a few mA, is possible without any great problems. If
you need more than this, you should think again.

Best Wishes

 

[Jan Panteltje]

On a sunny day (29 Mar 2004 02:40:51 -0800) it happened
muralipmanohar@hotmail.com (pmm) wrote in
<1f1fe31f.0403290240.3836135e@posting.google.com>:

Hello all
i want to power up a 3.3v IC which i want to place on the target
board.it is Connected to COM port of the PC is there any chance of
generating a 3.3v from the unused pins of the serial cord which is
connected to COM port of PC .(only three pins are used by me
presently those are 2,3,5)tranx ,receiv and GND)
If any body of you can help me with it i will be thankful
Regards
PMM

Yes, you can use the control signals RTS CTS and 2 LEDs in series as a zener

 

[Spajky]

On 29 Mar 2004 02:40:51 -0800, muralipmanohar@hotmail.com (pmm) wrote:

i want to power up a 3.3v IC which i want to place on the target
board.it is Connected to COM port of the PC is there any chance of
generating a 3.3v from the unused pins of the serial cord which is
connected to COM port of PC .

get it from nearby Usb pin & reduce it to 3,3V.

-- Regards, SPAJKY ÂŽ
& visit my site @ http://www.spajky.vze.com
"Tualatin OC-ed / BX-Slot1 / inaudible setup!"
E-mail AntiSpam: remove ##

 

[John Triactor]

see my arm board,

we use USB 5.0 V and dc -convertor is 3.3 V


http://arm.web7days.com

 

[pmm]

"Roger Hamlett" <rogerspamignored@ttelmah.demon.co.uk> wrote in message news:<lDT9c.54$B_1.29@newsfe1-gui.server.ntli.net>...

"pmm" <muralipmanohar@hotmail.com> wrote in message
news:1f1fe31f.0403290240.3836135e@posting.google.com...
Hello all
i want to power up a 3.3v IC which i want to place on the target
board.it is Connected to COM port of the PC is there any chance of
generating a 3.3v from the unused pins of the serial cord which is
connected to COM port of PC .(only three pins are used by me
presently those are 2,3,5)tranx ,receiv and GND)
If any body of you can help me with it i will be thankful
Regards
PMM
The first question is how much current you need?. The second question, is
whether this is only ever going to connect to 'desktop' PC's, or might be
used with a laptop?. The third question is what software will be controlling
the serial port?.
Yes, you can use a small switching regulator to give 3.3v, with good
efficiency from the handshake lines. You can 'wire OR' the available lines
with diodes to increase the available current. There are a series of
problems though. The 'active' state for RS232, is a -ve output voltage.
Hence you either need to control the lines yourself, and take them to the
inactive state, or design the converter to include a voltage inverter (like
the little Maxim switched capacitor inverter). Quite a lot of laptops,
'stretch' the RS232 specification, and only run the bus at 5v. This reduces
the total power available.
A supply offering just a few mA, is possible without any great problems. If
you need more than this, you should think again.

Best Wishes

Dear Mr Roger Hamlett
thank you for the reply
here are the answers .and my coworker told me that it uses a charge
pumps kind of circuit i cant use IC here i have to use only discrete
if you can help me with a schematic or a link to the page i will be
thank ful to you

The first question is how much current you need?. well 100ma will do
The second question, is whether this is only ever going to connect to 'desktop' PC's, or might be used with a laptop?. the target board i have been using to develop SW is use in industrial environments monitered by a PC so i am sure it is desktop PC on Windows Plat form
The third question is what software will be controlling the serial port?.
there is no SW till i have contacted using hyper terminal from my DSP

board i need to write a separate code using C or C++ on windows
environment
i am poor at HW designing
thanks in advance
PMM

 

[pmm]

Spajky <Spajky##@volja.net> wrote in message news:<nvpg609af1v247cgejvje3idpef8ktthkj@4ax.com>...

On 29 Mar 2004 02:40:51 -0800, muralipmanohar@hotmail.com (pmm) wrote:

i want to power up a 3.3v IC which i want to place on the target
board.it is Connected to COM port of the PC is there any chance of
generating a 3.3v from the unused pins of the serial cord which is
connected to COM port of PC .

get it from nearby Usb pin & reduce it to 3,3V.

-- Regards, SPAJKY ÂŽ
& visit my site @ http://www.spajky.vze.com
"Tualatin OC-ed / BX-Slot1 / inaudible setup!"
E-mail AntiSpam: remove ##
i am working on a DSP target board using PC .DSP is communicating

using serial port of the PC
the chip i have added works on 3.3v.so using any wires of serial port
i want to power it up with out using an extra bulky power supplies
regards
PMM