Monday, September 2, 2013

More From USB

Good Morning and welcome back everyone. Hope you guys are doing fine. As the title says this post will be about USB port and another alternative use of this already very versatile and widely used port.

Let's talk a little about USB!

USB stands for Universal Serial Bus, its an Industry standard that defines cables,connectors and communication protocol used in a bus for connection, communication and supply power between computers and other electronic device or peripherals . In this day and age USB probably is the most used port in our day to day life as we charge our phones with it, connect numerous peripherals with computer with it and use many other devices that have this port which is really very convenient.

Like I was saying USB port not only communicate and connect but also provide power to the device and this power can be used for many other things too, all you have to know is which Pin is used for what purpose.

Voltage and current:

A typical USB ports have standard 5.0V and can vary slightly and the current might start from 350mA to couple Ampere depending on the source. Although modern USB power delivery can deliver up to 100W it is not directly achievable, you will be needing some more circuitry to get it even if your source supports it. So let's think about typical scenario and think about 5V 1A as the standard. Question is what can we do with this power. Well you can easily make a light for your keyboard if it doesn't have any back-lighting, you can run a small fan with it, how about powering couple of Infrared LED to give your laptop webcam some night vision capability! So as usual the possibility is infinite and you can pretty much do anything you want with this available power.

What to do?

You will need an USB Cable like this or any other type that can be connected with the host system for example your Laptop.

Now cut it in half. Well not exactly half more like according to your will. If you do so you will find 4 cables inside of it(If it is a USB2.0 cable).

To get the power we will only need the 5V Red wire as supply and the Black Ground wire as return path. We won't be needing the differential pair on this case. If there is no color coding you might want to use a continuity test to determine which one is which.

USB2.0 Pin configuration

USB3.0 Pin Configuration

An important note here, both USB2.0 and 3.0 has four common pins and they have the same alignment so you can get the power from either of them just fine.

An USB Powered LAMP

Now you can harvest the power from USB and do whatever you want with it.

Warning :
1. Do Not Short Circuit the power carrying wires. It might cause damage to the USB port.

2. Double check polarity before connecting.

So happy experimenting and have a good day.


1. Wikipedia Page on USB.

2. My other blog posts.

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