[Novalug] USB connector to switch between 2 devices

Peter Larsen peter@peterlarsen.org
Sat Mar 28 20:49:47 EDT 2020


On 3/28/20 7:35 PM, Jon LaBadie via Novalug wrote:
> slightly OT, but at least mentions Andriod Auto  :(

I've just come of a long thread about that with my father .... so I'm
prepared :D

> After 16 yrs in one car, I got a new car.  One of its
> features was "11 USB ports".  HA HA, they really mean
> ONE USB port and ten charging only ports.

Sorry - if they did that you should send the darn thing back. At the
very least if the car is built to depend on a phone app like Android
App, you need at least one additional data port for AUX/music and at
time the car has additional features.  I have to admit that when I got
my Prius in 2012 I inserted a USB stick with a huge portion of my music
library - and I haven't moved it out since. I don't carry the same
amount of files on my phone (I guess I could but that means other stuff
would have to go) so it's an easy way to 'set and forget' a play source.

For those not familiar with Android Auto - it looks like the car
manufactors FINALLY figured out they couldn't compete with mobile phone
apps and features (took them long enough) and instead both Android and
Apple (have no idea about the apple thing - other than the very big
architectural lines). The short and very simple version is, that the
apps screen and sound is put on the display in the car, and you can
interact with it as if it ran on the phone.  Android Auto adds a few
other features like enforcing hands-free mode, so you cannot click
around while driving etc.  It's all voice controlled.

My car is a tiny bit too old to use the wired setup to activate this.
But I can use it by simply running the app on the phone and using
Bluetooth for audio. Works "good enough" to be useful.  But the idea is,
that the moment you plug your phone into the car, the app activates and
you get all the "advanced" features like navigation, music,
text-to-audio for text messages and a lot more loaded automatically.  On
a business trip I rented a car that had this feature, and it worked
really well. The car screen is often much larger than your phone in size
and resolution, so the app looks really great on it.

> I want to use the ONE port for two purposes, plug my
> phone in (Android Auto) and a memory stick for some music.

So do recall, that Android Auto does provide the music side. You can tie
a lot of different apps, like Pandora or other music libraries to it.
Your phone can access SD CARDs you put in the phone and hence you get
quickly get hundreds of gigs or more of space for music files so you
don't have to download them.  Meaning, you can use one device for all of it.

Alternatively use a second phone/device that is just getting power and
use wireless transfer. There are gadgets like this
https://www.amazon.com/SanDisk-Connect-Wireless-Stick-Flash/dp/B00ZCFYT5K?th=1
which to me looks like a sure-to-lose device - but who knows. It should
be permanently in the car, and your phone just connects to it when you
sit in it.

> The one port will not accept anything on a usb hub,
> things must be directly connected.  So any device that
> creates multiple usb ports from one port is not useful.

Are you SURE? From a protocol perspective there really isn't much of a
difference - the "magic electrons" are inside the hub - to the computer
it just communicates to multiple devices over the same wire (every USB
device has a unique address - it has to use this to talk to the device
anyway).

> 
> I'd like to find a cable/device that allows for
> switching between two (or more) things plugged
> in but makes it look like a direct electrical
> connection from one usb cable.

That doesn't sound like the right solution to me. What good is the USB
stick if it's not connected?  I feel pretty sure predicting you'll
eventually find a way to link everything over the phone - perhaps by
increasing it's storage capacity or just caching songs on a smaller
storage depending your mood.

Anyway - I would definitely go the wireless route if you absolutely want
a car that limits you like this.  USB hardware - in particular USB B
stuff is very very very cheap. UART chips are 10 cents or so when you
just buy ONE. In other words, I would be extremely surprised if the car
couldn't be "fixed" to allow you to use all 10 ports.

USBs are serial devices with addresses. A bit more advanced than I2C but
it's not really that complex. That's why it's all over the place.
They're cheap to produce, easy to use.

> I found a switch/cable that allows turn on/off a
> single usb device.  It solved a different problem,
> the electronics stopped seeing the memory stick
> after a while.  Switch off / on then made it look
> like I had removed and reinserted the stick.
That sounds like it's time to find a new stick. I had one that started
behaving odd at some point, and eventually it just stopped. If you don't
have a copy of the content elsewhere I would suggest you extract the
data and find a new stick.

> 
> I would like the same thing between multiple devices.
> Any ideas?

A Powered USB hub is the best way. That's in essence what should be in
the car already.

The reason some ports are power only were security based initially. As I
laid out above, the price of UART chips are so cheap it really makes NO
sense not to have the data.  Of course if your kids devices have
"crap-ware" on it you definitely don't want it to interfear with your
console in the car. That's easily solved by having one UART for the
driver and another for everyone else.  It really makes no sense that
nobody else can play music through the USB. After all, we can do that
through BlueTooth already.

Still - I would send an angry letter to who-ever marketed your car as
having 11 USB ports since only one is active.
-- 
Regards
  Peter Larsen



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