É frustrante ter hardware mais antigo apenas sentado em torno de coletar poeira ou ficar no caminho, então se ele puder ser reaproveitado e tornar-se útil novamente, então é motivo de alegria. A postagem de perguntas e respostas do SuperUser de hoje discute as possibilidades de redirecionamento de um antigo dispositivo de hub USB 1.1 para um leitor curioso.
A sessão de perguntas e respostas de hoje nos é oferecida por cortesia do SuperUser, uma subdivisão do Stack Exchange, um agrupamento de sites de perguntas e respostas conduzido pela comunidade.
Foto cedida por Alexandros Kostalas (Flickr).
A questão
SuperUser reader user1049697 quer saber se é possível usar um antigo hub USB 1.1 para carregar seus dispositivos:
I have an old USB 1.1 hub and I was wondering if it could be repurposed for something useful. Would it be possible to connect it to a wall charger that has a built-in USB outlet and use the hub to get 4 USB charging ports? Do USB hubs not work well when connected to wall outlets?
The image below shows a hub similar to the USB 1.1 hub I have:
Image
(Update) I did try this with some devices and the results are as follows:
My old Android 2.3 device will charge, albeit very slowly.
My iPhone 5S will not charge at all.
É possível usar um hub USB 1.1 antigo para carregar dispositivos?
A resposta
O colaborador do SuperUser Bob tem a resposta para nós:
Unfortunately, it really depends on the specifics of the implementation of both the hub and the device.
The vast majority of simple hubs do not really implement any sort of power control. They will just connect the USB power lines directly to either their host or an external (regulated) power supply, which means you would effectively be sharing the capacity of the power source over all ports.
In practice, however, USB charging gets quite complex. The bottom line is that your USB 1.1 hub will probably charge your peripherals, but at a reduced rate. This is not because the hub is actively limiting the current output, but because peripherals will limit the current they draw unless they can positively confirm the host is capable of supplying that current (to prevent damage to hosts that cannot).
This reduced rate depends on the specific peripheral and the specific hub, but it likely ranges from 100 mA to 500 mA, which is far less than a modern smart phone’s maximum (over 1,000 mA).
To elaborate:
1. If the host implements some kind of power control, then the peripheral must initiate a data connection and negotiate properly. Even though this is technically required by the specs (except the newer battery charging specs), some peripherals might not do so. I imagine most smart phones will at least try, but there are many ‘dumb’ USB peripherals that will not.
2. In the case of a hub connected to a USB power supply without a proper host, it might not work at all.
3. Negotiation is as follows:
Each peripheral is permitted to draw one unit load without negotiation. Each peripheral should communicate with the host to request more units.
USB 1.1 and 2.0 define one unit load as 100 mA, with a maximum of 5 unit loads (500 mA).
USB 3.0 defines one unit load as 150 mA, with a maximum of 6 unit loads (900 mA).
4. Modern devices often need more power (smart phones often draw 1,000 mA – 2,000 mA).
5. There is a battery charging specification that deals with this. Read through the article “How USB Charges Just About Any Electronic Device” for details on how its negotiation and detection works, but that is not too important.
The charging limit is 1,500 mA, but only if the data lines are shorted together (or respond as if they have been). This is not the case with a data-capable host like a USB hub. There is an additional profile that deals with this, but a USB 1.1 hub probably does not implement it.
With a non-compatible host, most smarter peripherals will fail to detect a high-capacity source and will therefore fall back to charging at 500 mA at most. This means your USB hub will likely charge the device at a significantly slower rate than plugging the peripheral directly into the charger.
5. There are some other specs such as Apple’s protocol, Qualcomm’s quick charge protocol, etc. They all have their own detection and negotiation methods. They will also not work with a USB 1.1 hub.
6. There is a newer USB Power Delivery spec, but almost nothing implements it yet and it deals with all sorts of wacky things like different voltages.
Tem algo a acrescentar à explicação? Som desligado nos comentários. Quer ler mais respostas de outros usuários do Stack Exchange com experiência em tecnologia? Confira o tópico de discussão completo aqui.
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