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| TRS connector with isolated switch? |
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| ElectricCrowbar:
I have this portable game system that inexplicably didn't come with a courage headphone jack. I've decided i want to try to add one. Incidentally its an Odroid Go[1] and for the price it's pretty lovely. I have to work around some limits here. Mainly that i can't control the gain of the amplifier. I more or less have a static output volume to work with. Also i'm going for minimal foot print here. So i'm trying to keep to passives and don't easily have access to regulated power. So, I started with the speaker is on a simple dongle: I initially tried to add a switched or"Normalized" headphone connector like this: While it does work the impedance difference between the 8Ω speaker and the headphones overdrives the headphones pretty badly. It's very loud and distorted. I can add a voltage divider to lower the volume, but that also lowers it for the speaker. Just like the headphones are too loud unmodified, "Just right" for the headphones is inaudible for the speaker. I think I need to attenuate the feed to the headphones and not the speaker. If i add a switch and a trimpot i can make my volume adjustment and use a switch to flip between headphones and the speaker: This will work (I think) but it's also not convenient. Modding the case for both a headphone jack and a second switch feels a little gross to me. I've found some TRS connectors that claim to have "isolated switches" and thought mayabe i could use that to make the switch automagically: https://www.cui.com/product/resource/sj2-3512d-smt-tr.pdf But i've found the schematic kind of confusing: I ordered one to be sure but the "isolated" switch "looks" like it has a relationship with the Ring on the tRs connector. I'm not sure what it's trying to tell me. So my questions are this: * Is this the best way to go or is there a more simple way? * Is the the switch in the CUI connector i liked above actually isolated. How do i search for this kind of thing. It's proved difficult on digikey [1] - https://www.hardkernel.com/main/products/prdt_info.php?g_code=G152875062626 please excuse the crudity of my schematics, i'm pretty new to this, i didn't have time to draw it to scale or paint it. |
| oPossum:
Put a resistor between the S terminal of the TRS jack and the amplifier. That will reduce the power to the headphones, but not to the speaker. |
| Richard Crowley:
This circuit will: 1) send audio to the internal speaker when nothing is plugged into the jack. 2) cut off the audio to the internal speaker when you plug something in 3) Send audio to both the tip (left) and ring (right) of your headphones/earbuds/whatever. 4) Attenuate the signal when something is plugged in. A) The value of the horizontal ("series") resistor is selected for tolerable attenuation of the internal speaker. B) The value of the vertical ("parallel") resistor is selected to adjust the attenuation of the headphone. |
| ElectricCrowbar:
--- Quote from: Richard Crowley on July 24, 2018, 06:13:23 am ---This circuit will: 1) send audio to the internal speaker when nothing is plugged into the jack. 2) cut off the audio to the internal speaker when you plug something in 3) Send audio to both the tip (left) and ring (right) of your headphones/earbuds/whatever. 4) Attenuate the signal when something is plugged in. A) The value of the horizontal ("series") resistor is selected for tolerable attenuation of the internal speaker. B) The value of the vertical ("parallel") resistor is selected to adjust the attenuation of the headphone. --- End quote --- This has the side effect of current limiting the speaker doesn't it? |
| Richard Crowley:
--- Quote from: ElectricCrowbar on July 24, 2018, 05:50:28 pm ---This has the side effect of current limiting the speaker doesn't it? --- End quote --- Yes. That is why you will see my note (A): --- Quote ---A) The value of the horizontal ("series") resistor is selected for tolerable attenuation of the internal speaker. --- End quote --- But that is as good as you can expect with a simple contact-closure switch function. It takes more switching to use an attenuator that is completely switched out of the circuit when using the speaker. If you really want a proper attenuation function that doesn't affect the internal speaker, you will need a more complex switching circuit. There are some jacks that have form-C (SPDT) switches rather than the simple switch in your example. Too bad there is no volume control in your gadget(?) else you might be able to use that contact closure to "diddle" the volume control for lower level when using the headphones. |
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