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Current I can drag from a RS232 PC port (COM1)?????

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nikaoj13

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

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