tim77777:
I can't measure 5mA. There seems to be much less than that.
This is because when the MIDI line is set at the idle state it draws no current.
Then when you send a MIDI message the current draw fluctuates between no current and 5mA depending if the serial is transmitting a zero or one at this time.
If you are trying to measure this with a DVM you have two problems:-
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The current you will see is an average current which will depend on the message contents and the number of messages you will transmit per unit time.
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Your DVM probably won't measure such rapid pulses anyway.
To measure the current you need an oscilloscope, measure the voltage across the series resistor and do the sums.