# How to detect if a TRS cable is connected to a MP3 player output?

Imagine I have a MP3 player and one male-to-male TRS cable that could be connected or not to the output of that MP3 player on END1. By having a multimeter on the other end END2 of the cable, how could I detect if the cable is connected there or not?

How do I have to do in order to proceed on that?

This is the multimeter I have:

and this is END2 which I will use for my measures:

Could you let me know on what position do I have to configure the multimeter and how to interpret the measures? I'm a bit new on electronic so details are welcome for me.

Thanks!

• Measure the resistance. Or perhaps very low current source and see if anything clamps on the other end. Jun 7, 2020 at 9:48
• Why do you need to know that and what do you do with the information if it is there or not? I am asking this because depending on the output stage of the MP3 player, it may not be possible to detect its precence by using a multimeter. Jun 7, 2020 at 10:09
• Your multimeter is not intended for signal measurements. It belongs to lowest hobby gear category. One can check with it resitances, DCvoltages. and few amps of DC current. It has quite good CAT rating for AC voltages, but those ratings can in low cost equipment be worth less than the ink which was used to print the rating.
– user136077
Jun 7, 2020 at 17:26
• (continued) But if those photos are your own shots you could earn some money by taking photos. They are a light year ahead from the ordinary hobby shots.
– user136077
Jun 7, 2020 at 17:33

The output signal of ordinary music players for headphones or external amp isn't detectable with your meter. It hasn't low enough AC voltage range. You have 200VAC and 500VAC ranges. The signal (=AC voltage) can be less than 2 volts. In theory at the 100VAC range the last number can show something, but the result is unreliable.

The higher, say 200kOhm or 20 MOhm resistance ranges can show something less than "over range" when connected from sleeve to tip or sleeve to ring and there's the player connected. The output circuit of the player can conduct a little the test current that the meter outputs at resistance ranges.

The shown value can be unstable and it can grow to "over range" as capacitors get charged. Keep your fingers off, the must not be a part of the measured circuit. Compare the result with a surely unconnected absolutely identical cable to reveal method error and leakage in the cable.

I guess you wanted info of the capabilities of your meter. Otherwise you would sinply look at the cable end with bare eyes.

• so does that mean I have no option for it? Jun 7, 2020 at 10:34
• This meter cannot detect weak signals. It can measure much weaker DC, but audio signals are AC voltages. Resistance measurement can detect if there's connected something which isn't pure insulator. In resistance ranges the meter tests what's connected by trying to feed a weak DC current. "Over range" means it found nothing which is conductive enough.
– user136077
Jun 7, 2020 at 17:13

Depends on how the output of the player is configured. When the player and its output Amplifiers are on, they would try to keep the voltage between GND and L/R at zero. By adding a very weak bias to e.g. L vs GND, i.e. 470k to 5V, you would see the bias voltage going away once it is connected. Using a multimeter, you would see a noticeable value change when you are in resistance or diode mode without using a bias.

When the player is off, there would still be an internal path from L/R to GND which would change the reading in diode and resistance mode; Measuring the bias voltage would probably work as well.

• I added an image on my voltimeter on my question. Could you let me know on what position do I have to configure the multimeter and how to interpret the measures? Thanks! Jun 7, 2020 at 10:03
• Your best chances are the 200k Resistance Setting or the "Diode" setting at (next to 200 V~). What are you trying to accomplish here ? Jun 8, 2020 at 11:18