Control an LED via USB/RS232 adapter
Today I connected my USB to serial adapter to my computer. Then I looked up which pin is TXD and which is GND. Then I used python's serial library to switch on TXD, connected TXD to GND and the result can be seen here:
Why does this work? Because there is a limiter that limits the power so the LED does not break. If I connect RI and TXD then via an LED it shines, plus RI's state, read by python, turns from off to on.