Current I can drag from a RS232 PC port (COM1)????? - Electronic Circuits Projects Diagrams Free

nikaoj13 · 11th March 2005, 05:01 PM

Does anybody know how much current can I drag from a Rs232 of a PC. I have been trying to use signal DTR (pin 4 of the DB9) but I face a strange situation.

1) DMM reads 11v without charge
2) As soon as I connect it to a 3.1 regulator voltage comes down to 1.92V.

I have been searching on the WWW but I can´t find any information on this issue.

Thanks in advance

Joaquin Arechaga

williB · 11th March 2005, 05:40 PM

i think that you cant really use the RS232 port to power anything..

mstechca · 11th March 2005, 06:07 PM

why use an RS-232 port to suck current? Why can't you just use a power adapter and suck current from that instead?

mangart · 11th March 2005, 06:08 PM

Dont be so shure about it!
Do you remember those old PC mouses 10 year ago ,they were pluged directly to any serial port on your machine.
So they get their power from COM port.
Check this link: http://www.hut.fi/Misc/Electronics/c...s/rspower.html

Juglenaut · 12th March 2005, 04:52 AM

The comps the drove those beasts are also obsolete.

7 to 10 mA is that alot of current to you??

Most devices that require drive current today are 100mA to 500mA.

Also most devices that use those ports have an adapter as well or uses the provided current to run a simple IC for data transmission purposes.

mangart · 12th March 2005, 10:14 AM

"""""The comps the drove those beasts are also obsolete. """""
Com ports on those old PCs have totaly identical electrical characteristic as PCs today.

""""""""7 to 10 mA is that alot of current to you?? """""""
Todays microcontrolers (PICs,AVRs.....) have curent consumtion in the range of microampers , so if you want one of them to hook on your COM port you can do that without any extra battery or adapter power.
Todays LEDs need 1mA to light.
Curent trend in electronic is to have devices with small power consumption.

nikaoj13 · 14th March 2005, 01:13 PM

HI all,

just did a practical test. Serial port is only able to give 8-10 mA with voltage around 3V....not good enough!!

thanks anyway!!!!

JohnBrown · 14th March 2005, 03:01 PM

Actually it depends on the serial port. The old style 1489/1488 IIRC, were able to source quite a bit of current, and ran at +/- 12V (ish). A lot of the newer stuff has MAX232 or equivalent chips, and may only produce +/- 3 to 5 V. I've powered things from serial ports before, OR the control lines (DTR, RTS) and the TXD line together using diodes.
You are unlikely to damage anything, since most RS232 interfaces are current limited, but don't blame me if you do.

Found this pdf, knew I had it somewhere!

11th March 2005, 05:01 PM	(permalink)
nikaoj13 New Member	Current I can drag from a RS232 PC port (COM1)????? Does anybody know how much current can I drag from a Rs232 of a PC. I have been trying to use signal DTR (pin 4 of the DB9) but I face a strange situation. 1) DMM reads 11v without charge 2) As soon as I connect it to a 3.1 regulator voltage comes down to 1.92V. I have been searching on the WWW but I can´t find any information on this issue. Thanks in advance Joaquin Arechaga

12th March 2005, 04:52 AM	(permalink)
Juglenaut Experienced Member	The comps the drove those beasts are also obsolete. 7 to 10 mA is that alot of current to you?? Most devices that require drive current today are 100mA to 500mA. Also most devices that use those ports have an adapter as well or uses the provided current to run a simple IC for data transmission purposes. __________________ Your website has been blocked

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11th March 2005, 05:40 PM	(permalink)
williB Experienced Member	i think that you cant really use the RS232 port to power anything..

11th March 2005, 06:07 PM	(permalink)
mstechca Experienced Member	why use an RS-232 port to suck current? Why can't you just use a power adapter and suck current from that instead?

11th March 2005, 06:08 PM	(permalink)
mangart New Member	Dont be so shure about it! Do you remember those old PC mouses 10 year ago ,they were pluged directly to any serial port on your machine. So they get their power from COM port. Check this link: http://www.hut.fi/Misc/Electronics/c...s/rspower.html

12th March 2005, 10:14 AM	(permalink)
mangart New Member	"""""The comps the drove those beasts are also obsolete. """"" Com ports on those old PCs have totaly identical electrical characteristic as PCs today. """"""""7 to 10 mA is that alot of current to you?? """"""" Todays microcontrolers (PICs,AVRs.....) have curent consumtion in the range of microampers , so if you want one of them to hook on your COM port you can do that without any extra battery or adapter power. Todays LEDs need 1mA to light. Curent trend in electronic is to have devices with small power consumption.

14th March 2005, 01:13 PM	(permalink)
nikaoj13 New Member	HI all, just did a practical test. Serial port is only able to give 8-10 mA with voltage around 3V....not good enough!! thanks anyway!!!!