Tablet charging in host mode - Page 1
Forum section: electronics / projects

author: gaminn
author_rank: Frequent Contributor
timestamp: July 30, 2019, 07:56:11 pm
content: Hi,I'm looking for +- 8" 1280 x 800 low end cheap tablet that can charge itself while in USB host mode. I need to connect USB keyboard (or another USB device) to the tablet and at the same time I want battery to be charging.I think there are 3 options:1) USB Accessory Charging Adaptor2) Wireless charging3) Separate USB and charging connectorDo you know any low end tablet that support at least one option?

author: frozenfrogz
author_rank: Frequent Contributor
timestamp: July 30, 2019, 08:25:14 pm
content: I do not really see the problem you are talking about. All you should need is an OTG adapter and a y-connector cable with two USB A plugs and one USB A socket to connect your keyboard to (or other device).The y-connector cable usually would have one fully connected plug and one with only +5V and GND wired in parallel. This can be hooked up to a charger / powered USB port.

author: gaminn
author_rank: Frequent Contributor
timestamp: July 30, 2019, 08:40:31 pm
content: This won't work. In host mode (USB keyboard connected to the tablet) the tablet supplies 5V to the bus. There is no way to charge the tablet via the same USB port. Unless the tablet support Accessory Charging Adaptor specification where the tablet doesn't supply 5V on the bus and charges from external charger that is connected on the same bus.

author: SiliconWizard
author_rank: Super Contributor
timestamp: July 30, 2019, 08:58:31 pm
content: Have you taken a look at this thread?https://electronics.stackexchange.com/questions/34741/can-an-android-tablet-serve-as-usb-host-and-be-charged-simultaneously-through-a

author: gaminn
author_rank: Frequent Contributor
timestamp: August 01, 2019, 01:48:24 pm
content: Yes. Obviously, there are some mainly manufacturer specific modifications that will enable charging in host mode.There is probably no other way than to buy/borrow some cheap tablets and try if there is a possibility to charge in host mode. And when the manufacturer discontinue that tablet you have to search again for new one with this feature.

author: SiliconWizard
author_rank: Super Contributor
timestamp: August 01, 2019, 02:00:53 pm
content: Don't think there's anything more you can do.You can also hope that someday implementing at least 2 USB ports on tablets will become "standard", but I wouldn't hold my breath...

author: joeqsmith
author_rank: Super Contributor
timestamp: August 01, 2019, 02:08:18 pm
content: I used a Lenovo 8" Windows based tablet to run LabView on. There was a trick where I could short the data pins when powering up the unit. This would put the unit in charge mode, then remove the short after it booted. This allowed the USB to communicate. I ended up making a custom cable for it. Worked great. I tried it with some new cheap Windows tablets I bought a couple of years ago and it wouldn't work with them.

author: gaminn
author_rank: Frequent Contributor
timestamp: August 01, 2019, 02:13:33 pm
content: Quote from: joeqsmith on August 01, 2019, 02:08:18 pmThis is exactly what I've done with my LG G3 phone.

author: angust_uk
author_rank: Regular Contributor
timestamp: August 01, 2019, 05:39:19 pm
content: I did exactly this with a cheap Windows 10 tablet. In my case I needed to run the cables out of the back of the unit so I soldered directly to the VBUS, GND and D+/D- signals of the Micro USB socket on the PCB, injecting 5V on VBUS. This may not be the best way of doing it but it worked for me!

author: Lord of nothing
author_rank: Super Contributor
timestamp: August 03, 2019, 11:14:04 am
content: If you not need the "Tablet" Features you can use a smal pc for who have a lot of power and can use by a plug.

author: NiHaoMike
author_rank: Super Contributor
timestamp: August 03, 2019, 03:19:11 pm
content: If you don't mind some modding, connect a 4-4.1V supply in parallel with the battery, current limited to a 1C rate or less.