TRRS connections

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nicolerenee0922
Posts: 10
Joined: Sat Aug 05, 2017 7:16 pm

TRRS connections

Postby nicolerenee0922 » Sun Aug 13, 2017 1:53 pm

The schematic and the directions on the website show two different connections for the TRRS. The directions have TRRS V going to the ground rail and TRRS Gnd going to left amplifier pin 7. The schematic shows TRRS GND going to the ground rail and TRRS V going to left amplifier pin 7. Can someone tell me which is correct?

kckerbypatel
Posts: 23
Joined: Sat Aug 06, 2016 8:59 pm

Re: TRRS connections

Postby kckerbypatel » Mon Aug 14, 2017 7:20 pm

Yes - the one with V to ground is correct. The labeling on the TRRS jacks is misleading. The TRRS jacks are marked with a different standard than is current on most phones (see https://en.wikipedia.org/wiki/Phone_connector_(audio)#TRRS_standards), so if we connect the terminal marked "V" to ground, we're actually connecting the CTIA TRRS ground conductor to ground on our circuit.
K.C. Kerby-Patel, EclipseMob Hardware Team Director, Assistant Professor at University of Massachusetts Boston

tlauzon
Posts: 2
Joined: Sun Oct 16, 2016 5:44 pm

Re: TRRS connections

Postby tlauzon » Wed Aug 16, 2017 11:13 pm

KC, it seems to me that the microphone connection on the TRRS jack (labeled GND) should be connected to pin 1 of U6 and the ear piece connection (L or R) on the TRRS jack should be connected to pin 7 of U5. You generate a tone in the phone which has to come out through the ear piece speaker connection. The output of the receiver has to get back into the phone via the microphone connection. The instructions have the connections reversed.

When I connect the way that I described, I get a spectrum with a peak at about 22 kHz according to the app. Previously, the spectrum was flat for the most part. When tested by the app, the signal is still not detected.

skristof
Posts: 8
Joined: Fri Aug 11, 2017 5:24 pm

Re: TRRS connections

Postby skristof » Thu Aug 17, 2017 12:46 pm

Based on the discussion so far, it seems that we still don't have a straight answer on how to wire up the TRRS connector. What is the "ground" on the breadboard anyway? Is it the - (negative) line in the power busses? If not, then where is it? I'd love to hear from a person who has built version 2, and has documented that their build actually works.

kckerbypatel
Posts: 23
Joined: Sat Aug 06, 2016 8:59 pm

Re: TRRS connections

Postby kckerbypatel » Thu Aug 17, 2017 1:47 pm

Tom, (nice to see you on the forum!) the TRRS connections are actually the other way around from what you've described. Pins 1 and 3 are the noninverting inputs of the multipliers (2 and 4 are the inverting ones), so they require a signal coming in - that's on the L or R audio output of the phone. The phone looks for audio signals on its mic input, which is how A/D conversion happens. Since it needs an input there, it gets connected to the output of the multiplier (pin 7).

skristof, I designed version 2, and I have also built it and got it to work. "Ground" on the breadboard is the two blue power rails as you described. The TRRS connector should be connected as I described in my previous post. Its labels happened to be marked using a different standard than is typical on most cell phones - it's marked Tip-Ring-Ring-Shield = R-L-V-GND, in that order, while most current cell phones use the CTIA standard, which is TRRS = R-L-GND-V.
K.C. Kerby-Patel, EclipseMob Hardware Team Director, Assistant Professor at University of Massachusetts Boston

A Street Gang
Posts: 1
Joined: Fri Aug 18, 2017 10:25 pm

Re: TRRS connections

Postby A Street Gang » Fri Aug 18, 2017 10:33 pm

We are new to the effort and scrambling to get ready. Unfortunately, there is only one Radio Shack left in our part of Utah. We were able to order out of state everything except the TRRS female jack. Can we substitute a standard 3.5 mm female jack? If so, how would we ground it? Is there something else readily available that could be used instead?


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