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Question Connect multiple USB devices to Android phones

Apr 24, 2020
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Hi folks.

I have an app on Google Play that ideally requires at least two USB devices to be connected to the Android device, namely a USB keyboard and a USB transcription foot pedal, and maybe a mouse too, without draining the Android device's power. The question is how to connect those devices to the Android device.

You can get USB hubs, like this:
https://www.amazon.co.uk/Charging-Adapter-Samsung-Galaxy-Xperia/dp/B01MXRFWXX

...but they don't appear to work with some phones, for example they don't work with my Vodafone - the connected devices work but the hub doesn't charge the phone, and the USB devices drain it so quickly that this won't be workable.

I then thought about Bluetooth. You can get Bluetooth keyboards/mice/pedals, but my customers won't spend that amount of money - the pedals in particular cost a fortune. If there was a hub that allowed the user to plug in up to 3 USB devices and then transmitted the signal via Bluetooth, that might work. The hub would have to be mains/USB- powered, because my customers won't want to keep putting batteries in it. However, I haven't been able to find anything like that.

There also has to be very low latency, which I assume means that sending the signal over wi-fi somehow won't work.

Does anybody have any thoughts or suggestions on how I could solve this?
 
Apr 24, 2020
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Unfortunately I don't think that gadget will work with all Android devices - not my Vodafone, for example. I need to be able to tell ONE solution to all potential customers of my software. At the moment I'm telling them to buy something suitable for their phone, but this just makes it complicated for them.

I'm thinking a Bluetooth solution would be better - how to convert USB peripherals to Bluetooth...
 

LRoger

Prominent
Apr 25, 2019
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Converting a wired device to wireless in itself is quite the challenge for the average joe, it is possible with use of an arduino project using a HC-05 but this clearly isn't a one for all solution by any means, is there any way that you can program the aforementioned app to make use of something like the previous link?
 
Apr 24, 2020
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I believe the problem is the Android device, rather than the app. I already tried a USB hub but it doesn't work with my phone, so it probably won't work with many others.

I had another idea which is rather convoluted:

First convert USB to 3.5mm using this:
https://www.dictaphones.co.uk/USB-to-3-5-mm-Jack-Converter-p/usb35mm.htm

...then convert 3.5mm to Bluetooth using this:
https://www.ebay.co.uk/itm/HIFI-Wireless-Bluetooth-2-in1-Audio-Transmitter-Receiver-3-5MM-RCA-Music-Adapter/202924050239?hash=item2f3f37473f:g:~EgAAOSwWEZeYzrU

Seems crazy, but would it work?

Obviously I can get those things and try, but it will take a week...
 

LRoger

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Apr 25, 2019
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umm.... that's a new idea to me haha physically makes sense but not theoretically, wouldn't your issue then become getting it to be seen as a peripheral device on the apps receiving side as the phone itself would see it as an auxiliary device. You're then left with the problem of only being able to connect to one device at a time as this example is for a single connection ^ and most if not all phones only support a single connection
 
Apr 24, 2020
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Physically you could get it to work with more than one device at a time by using the gadget that you first mentioned to me, the USB hub...

Not sure what you mean about peripheral device versus auxiliary device...?
 
I need to be able to tell ONE solution to all potential customers of my software.
You're targeting wrong device / platform with your app. Mobile phones were not designed to support multiple USB devices. On top of that, there are thousands (probably, more) of Android devices with various softwa re levels, OTG support etc.

The most "working" solution would be a powered USB hub with OTG adapter for the phone (USB-C or microUSB). Leave the phone on battery, and use the hub to power peripherals.
 
Apr 24, 2020
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Yes, I've come to the same conclusion. I can't change the platform, so I think I'll have to be content with having the OTG just power the peripherals - that will be adequate.

I must say, though, I thought my other idea was great fun: USB devices to powered hub, powered hub to USB, USB to 3.5mm, 3.5mm to Bluetooth transmitter. One rainy day I'll check and see if that works!

Thanks for the advice.
 
I don't see how a keyboard (or OP' "foot pedal") can be translated to analogue 3.5mm signal, and how the phone will convert this audio input *thats' all the Bluetooth will transmit) back to keyboard, mouse and foot pedal input.
 

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