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Ask HN: How to fake laptop connection via USB

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Ask HN: How to fake laptop connection via USB

#1

Post by pizu »

Hope we have some USB professionals here. I have an external audio sound are device that is USB powered and needs to be connected to PC/Mac/tablet for it to power up. The device has a built in mixer that offers direct monitoring, I've audio goes from input ports directly to outputs (skipping the PC). I would like to make the device work as a standalone mixer without the need to connect to a PC. I've connected the device to a USB wall socket/charger but the device doesn't power up. I suspect that the reason is that the USB charger only sends 5V power but not the data steam (to pin 2 and 3, as presumably PC does). Does anyone know if it's possible to hack the USB cable or USB wall charger to make the audio device think it's connected to a laptop? Or phrased differently, what does the device see when it's connected to PC vs a wall charger?

Re: Ask HN: How to fake laptop connection via USB

#2

Post by opless »

The device will see power, but very little else. USB chargers could leave the two data pins floating, tied together, or exhibiting various resistances between pins. Depending on what it's supposedly built for charging.

Here's a link to start you off with.

http://electronics.stackexchange.com/questions/123172/what-i...

Most usb devices will look for data before thinking about initialising.

Hard way to solve your problem: If you wanted to power it up and set it up for a certain configuration without a PC, you'd probably be best off starting to sniff the usb bus and possibly play back the results (YMMV) with an arduino or similar.

You'd need something along the lines of a bus pirate to do all that https://en.wikipedia.org/wiki/Bus_Pirate

Less Hard Way: Or if you're a software person, you could just sniff the usb bus of a virtual machine, but I imagine that you may miss certain bits of handshaking, then program an arduino or similar appropriately

Easier way: If the device has linux drivers you could hunt down a raspberry pi zero (or a regular one, or beagle bone or any number of other ARM linux boards) and just drive it from that.

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