I am interested in drawing power from an RS232 port so that it powers an external circuit, only I am not too sure where to begin. The RS232 port is not on the DTE side, but on the DTE side. I was able to measure
-7.59V DC and -25mA on the following PINs using a digital multimeter: RI, DSR, DCD, CTS.
Is it possible to draw power from this DCE so that I have +3.3V DC at approximately 140mA for my circuit? Let me know what you guys think.
Steph
Sorry, I meant to say: "The RS232 port is not on the DTE side, but on the DCE side."
Steph
S. Ethier wrote:
No. RS-232 ports do not deliver that much current. If you got 25mA, then you were lucky. I'll bet that the -7.59 v and -25mA did not occur at the same time. You probably had to short the output to get that much current.
-Robert Scott Ypsilanti, Michigan
Hello Steph,
The only way I see to achieve 140mA for very short periods is if your circuit could run on a low duty cycle and you provide a large cap that is charged via a current regulator that limits things to a few mA.
Just curious: Why do you need so much? Can the circuitry be optimized for lower power?
Regards, Joerg
Com ports vary enormously. I've had commercially designed interfaces looking for 10mA at +5V from two handshake lines that would work on SOME pooters but not others. Laptops are probably the worst in this regard, with rather wimpy implementations.
But 140mA? No way. Read the EIA standard and see what a compliant DCE/DTE port is expected to provide in the way of drive, and you'll understand why.
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