Any of you avionics gurus help me out?
I am making up my own radio/intercom harnesses - I know, I know - but actually, it's going quite well ..... but I have a small issue.
I have a Guardian iPad Mini mount with USB power. That end of it is fine - wiring diagrams on their website. However, it also has an audio cable with a 3.5mm plug. All looks simple - 4 rings - from the tip - left audio, right audio, ground, mic. So I don't need the mic so I can just terminate it and connect up the other 3. But when I use my tester to check which wire is which, I come up with a problem. Both audio leads fine - found them. Ground ring doesn't give any connection to the remaining 2 wires. The mic ring gives 6.7k resistance to one wire - nothing to the other (black - so I assume ground). I can see that the mic input might need some pull-down resistor which is built in so no problem. But the resistance across the remaining 2 wires is also 6.7k - ???????
So my question is this - where has my earth (sorry - "Ground") gone? Do I need to roll my own jack and cable - or is that going to blow something if I just use 3 wires and no resistor?
I am making up my own radio/intercom harnesses - I know, I know - but actually, it's going quite well ..... but I have a small issue.
I have a Guardian iPad Mini mount with USB power. That end of it is fine - wiring diagrams on their website. However, it also has an audio cable with a 3.5mm plug. All looks simple - 4 rings - from the tip - left audio, right audio, ground, mic. So I don't need the mic so I can just terminate it and connect up the other 3. But when I use my tester to check which wire is which, I come up with a problem. Both audio leads fine - found them. Ground ring doesn't give any connection to the remaining 2 wires. The mic ring gives 6.7k resistance to one wire - nothing to the other (black - so I assume ground). I can see that the mic input might need some pull-down resistor which is built in so no problem. But the resistance across the remaining 2 wires is also 6.7k - ???????
So my question is this - where has my earth (sorry - "Ground") gone? Do I need to roll my own jack and cable - or is that going to blow something if I just use 3 wires and no resistor?
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