What are the currents/voltages on the DB-9M(com-port) pins?

Question

Electronics

Hello. Maybe someone measured or knows how to measure?
There are definitely currents there, because to make the sensor work normally through the com port, I had to solder a 100 ohm resistor into the wire section connected to pin 9

Answer 1

voltage at RS-232 outputs from -12v to +12v.
in general, it would be necessary to read the documentation first, and only then solder.
Even after reading what is written about RS232 in Wikipedia, a lot of questions would be gone.

Answer 2

The characteristic is set by the MAX232 microcircuit

Answer 3

On modern PCs, the standard has not been respected for a long time. The levels will be at best + -8V, and the currents are rather meager. It was possible to power the device with a current of about 20 mA from the RTS line.

Answer 4

It is impossible to give an unambiguous answer + - 12 there or + -8, it all depends on the specific device,
in particular on the microcircuit that is used to create levels at the output of the RS232 port.
Depending on the microcircuit, the current can reach tens of milliamps, which is quite enough, for example, to operate a primitive temperature sensor or something like that.