USB Ground Lift

[mansr]

26 minutes ago, Cornan said:

Yes, it could mean that your DAC needs to see a 5v feed. You can possibly still do a USB ground lift, but for that to work the 5v lead needs to be attached at all time and the GND lead needs to have its own detatchable connection (for example a DC male plug and a DC female plug). When the DAC have started you can unplug the GND (but keave the 5v connected). This might work IF your DAC does’nt require GND as well. To find out you’ll need to do a little research among other users of your perticular DAC or just make your own experiment to see if it works or not.

If the DAC requires the 5V connection but works with GND disconnected, it means there's some other ground path back to the computer. In this case, disconnecting GND is a bad idea.

 

[mansr]

10 minutes ago, rikhav said:

Tried connecting voltage + and - to an LPSU but still DAC is not detected

Need to connect the USB header having voltage + and - to PC , then only DAC gets detected 

 

Not sure what to make of this

You must have ground connected to the host PC for detection to work, even if +5V is supplied separately. Once the high-speed handshake has completed, the ground can be disconnected. Full-speed devices need ground connected at all times.

[mansr]

1 minute ago, rikhav said:

My DAC has cmedia cm6631a USB interface so it's a USB 2 high speed

 

So I will try to experiment connecting ground with DC male and female pins so I can disconnect it later on

 

How can I connect only 5 volt plus to any external PSU?

Connect ground and +5V to the external supply. Also connect ground to the PC during the handshake.

[mansr]

7 minutes ago, sandyk said:

I presume that you mean 0 Volts of the external +5V supply.

I mean what I said. Connect USB ground and +5V to the corresponding terminals of the power supply. Connecting only one would be rather pointless.

 

7 minutes ago, sandyk said:

It doesn't need to be earthed

Of course not. I mean ground in the usual 0V reference sense.

[mansr]

36 minutes ago, sandyk said:

I think we may be talking at cross purposes here.

Perhaps a simple diagram also showing a USB ground switch may help the less experienced members  ?

  DAC                    PSU
+------+               +-----+
| +5V  |---------------| +5V |
| GND  |-----+---------| GND |
| D+/- |==#  |         +-----+
+------+  |  |
          |  |
          |  |            PC
          |  |         +------+
          |  +--<SW>---| GND  |
          #============| D+/- |
                       +------+

 

[mansr]

32 minutes ago, sandyk said:

Incidentally, anything further on the USB Widget  ?

Funny you should mention the USB Troll. It fell by the wayside for a while, but PCBs with a few tweaks are being made as we speak. My plan is to do some testing to find the best settings, then get rid of the switches to reduce component cost and assembly effort. (The switches are actually the most expensive parts.)

 

For those who missed the original discussion, the USB Troll is a device that automatically disconnects the ground when safe while providing an input for separate power.

[mansr]

1 minute ago, Ralf11 said:

you're going to call it  the USB Troll?

Feel free to suggest a better name.

 

1 minute ago, Ralf11 said:

if so, how about another version called  the USB Droll?

What would it do?

[mansr]

13 minutes ago, rikhav said:

So now I at least know with my DAC I need the ground to be connected for the DAC to be detected by host PC

That's always the case with USB. Detection works by the device pulling one of the data lines high relative to ground, which it can't do if ground isn't connected.