3DS Bluetooth Power Gate

01Power circuit

02Audio wiring

Why pin 1 caused static isn't confirmed yet. The likely reason is that it isn't a direct ground. It may reach ground through a ferrite bead or resistor, or it may be the headphone amp's sense or virtual-ground line. Either way, the module was measuring audio against a reference that moved. To confirm it, with the 3DS off and a plug in, measure resistance from pin 1 and pin 4 to board ground (pin 4 should read about 0Ω). Then, with the 3DS on and silent, measure DC volts from pin 1 to ground. A few ohms or any voltage on pin 1 means it isn't a true ground.

03Node reference

04Assembly order

1. Both control signals confirmedTP126 measured 1.8V open / 0V closed, cleanly above and below the NCP380 EN thresholds (1.2V min high, 0.4V max low), so no bias resistor is needed on that leg. TP49 measured 0.783V unplugged / 0V plugged. The unplugged reading falls between the two thresholds, which is why R2's pull-up is still required there.
2. Place the decoupling capsTack C1, C2, and C3 near where each will sit (IN of NCP380H, IN of NCP380L, and VIN of the BT module) before running the rest of the wiring.
3. Mount both switch ICsNCP380H and NCP380L on a small scrap of perfboard or dead-bug style, leads accessible for hand wiring.
4. Wire the ground bus firstTie NCP380H GND, NCP380L GND, BT module PGND, and board ground together. Ground is the reference every other measurement depends on.
5. Wire the power pathRail → C1 → NCP380H IN → NCP380H OUT → C2 → R2 top-tap → NCP380L IN → NCP380L OUT → C3 → BT module VIN.
6. Wire EN(H)TP126 straight to NCP380H pin 4. No extra resistor needed, since its swing is clean on both ends.
7. Wire EN(L)TP49, the R2 pull-up, and NCP380L pin 4 all land on the same node.
8. Power up without the BT module attachedConfirm NCP380L OUT reads correctly across all four open/closed × plugged/unplugged combinations (table below) before anything downstream is at risk.
9. Connect the BT module's powerVIN and PGND only, once the switching logic checks out clean on its own.
10. Prepare the module's audio inputRemove the two stock capacitors in series with the L and R inputs and bridge each footprint so the signal passes straight through. Leave AGND and PGND separate. Don't bridge them.
11. Wire the audioJack pin 2 → module L in. Jack pin 3 → module R in. Jack pin 4 → module AGND. Leave jack pin 1 unconnected. Keep these wires short, twisted together where you can, and away from the module's antenna.
12. Check that the jack still switches the moduleAGND now shares the TP49 node, so confirm it hasn't pinned that node low. Open the lid and unplug the jack: the module must power off, and TP49 must read above 1.2V. If the module stays on, move AGND to the jack's metal shell lug or a nearby board ground pad and listen for static again. Don't go back to pin 1.
13. Test with a metal plugPlug a metal 3.5mm plug into the jack and open the lid. The module should power on, and TP49 should read near 0V. Use a metal plug for this and every later test. A plastic dummy plug won't switch the module on with this wiring.
14. Check the uncapped inputs for DC offset and clippingWith the 3DS on and silent, measure DC from jack pin 2 and pin 3 to ground. You want close to 0V, under about 50mV. Then play something bass-heavy at max volume and listen for crunch. If either fails, fit 4.7–10µF caps in the L and R footprints instead of bridges. Larger caps block DC without muffling the sound the way the stock ones did.

05Expected states

Closed + plugged still reads off because Switch 1 has no input power to pass to Switch 2, whatever the jack is doing. That's the point of nesting them in series. Re-run the Open + Unplugged row after wiring the audio (step 12). "Plugged" always means a metal plug. A plastic plug reads the same as unplugged.

06Bill of materials