Input jack battery switch for digital ground

[st.mu]

Does anyone know how to wire the input jack battery switch (similar to the schematic here. basically only power on the circuit if the input jack is connected) if the audio ground should be different from the power ground?


The usual solution is to use a stereo jack and connect the negative end of the battery to ring. The ground will be connected if ring and sleeve are connected by the input jack, but this configuration forces audio and power to share the same ground.

I'm currently building a project with Electro-Smith Daisy and somehow the board is using split grounds DGND and AGND. Some weird things would happen if I connect the negative end of the battery to AGND. Not sure if it's a design problem, but the board will drain almost double the current and it causes noises in the audio output. As far as I experimented, the only way to fix the problem is to use battery on DGND and audio on AGND, but the usual design of jack battery switch doesn't work with separate grounds.

I can't figure out a way to wire the battery to achieve a separate ground. I actually have an audio jack with switched contacts, i.e. TRS each has a pair of pins that are connected to each other by default, but the pairs became open circuit if jack is connected. I can't find any examples of using this mechanism for battery switch. Is this configuration possible with this switched contact jack?

[ElectricDruid]

Welcome to the wonderful world of "mixed signal design", which is to say, the messy place where analog and digital overlap!

It's a nightmare, frankly.

In general, ground is ground. Analog grounds and digital grounds get separated because PCB packages need to know that these two bits need to be kept separate. If you just call them both "Ground", it'll tell you that you can link up some digital part with some nearby analog part, which contravenes all the best-practice rules about keeping digital ground currents away from analog ground currents. So instead we give them separate net names and treat them like they're two entirely different things. But ultimately, they'll meet up somewhere - they're connected together and they're therefore "the same thing". The point is that we need the place where they meet to be as close to where the power comes in as possible, so that the two sides (A and D) of the circuit act more like two separate circuits tacked onto the same power supply, rather than like one circuit all mixed up.

Consequently, the typical "jack switched" ground input like you describe presents problems. It acts like the point-furthest-back where we could connect the analog and digital grounds, but it is also very clearly a significant audio ground, so it's about the *last* place we want to be connecting all our digital circuits to. So...I dunno!

At this point, my usual policy is to look and see what other people have done (Plagiarise! Only be sure always to call it "research"!). Perhaps some Boss Digital Delay schematics might give us a few clues? How did they deal with this? There must be other examples out there, since there's no way we're the first people to come up against this problem.

[FiveseveN]

Use a transistor to switch 9V instead, with the jack only providing the control signal.

[st.mu]

I think I figured out the solution. There is a special type of audio jack that has isolated switches. The one I need is Switchcraft 13 or 113X. Basically they have two isolated terminals that will be connected when the input is plugged in.

[duck_arse]

Does anyone know how to wire the input jack battery switch (similar to the schematic here. basically only power on the circuit if the input jack is connected) if the audio ground should be different from the power ground?


The usual solution is to use a stereo jack and connect the negative end of the battery to ring. The ground will be connected if ring and sleeve are connected by the input jack, but this configuration forces audio and power to share the same ground.

this circuit could hardly be drawn any wronger. it shows the jack tip connected to the battery when no jack plug is inserted. when the plug is inserted, the battery connects to nothing, and the circuit remains unpowered.

it would be correct if the jack symbol was a stereo instead of a switched mono. but it isn't - hence, wrong.