Raspberry Pi USB Not Working

The Raspberry Pi has a USB hub for connecting a keyboard and mouse. These ports can be problematic at times, and you could find your input devices not registering when the Pi boots. This multi-page article looks into some of the reasons why this problem occurs.

Many people will go through this troubleshooting loop a finite number of times before realising that something is amiss. I seem to remember reading about how the Raspberry Pi was designed to work with any keyboard and mouse around the house, so why does my keyboard and mouse not work?

I tried five different keyboards from different manufacturers including Apple keyboards, however none worked. I then tried Linux compatible keyboards and many of those did not work either. After my 20th try, I decided to get the circuit diagram and soldering iron out and perform a little modification. I suspect many other people will encounter the same problems as me hence this article. The following sections of this article will show the design features of the USB circuit and the modification I experimented with. Of course, as soon as the soldering iron touches the board your warranty becomes invalid.

USB Keyboard and Mouse

At the time of introduction, many suppliers realised the compatibility issues and hiked up their prices. Suddenly a £5.00 keyboard ended up costing £25.00 simply because it was "Raspberry Pi Compatible", and since many parents did not want to disappoint their children, they paid for the over-priced peripherals. Linux is a great operating system if only there were more drivers for differing models of keyboards and mice, because most of the time it is very particular about the hardware it works with, and if you couple that with a USB power issue then there is a very narrow range of USB hardware that will work. This is obviously not a good thing since the concept of the Raspberry Pi is to reduce the cost of computing and to use whatever parts that one might have available in the home.

There are two main issues to consider where the USB keyboard and mouse are concerned. 1. The devices must be supported by Linux, and 2. The devices need to be electronically compatible with the Raspberry Pi hardware since the Raspberry Pi Board B provides 140 mA maximum to each USB port before the polyfuse trips. In addition, due to the simplistic power design of the Pi there are issues concerning the resistance across the polyfuse and the voltage drop they cause, and in a large-scale production, these minor design issues can become significant.

Unfortunately, the current limitation poses a limit on the range of hardware that will work, as many people will have wireless keyboards and mice requiring more power. It can be very frustrating if you finally receive your Raspberry Pi and find out that the keyboard and mouse that you were hoping to use will not work. Even more frustrating is when you find out that you will have to spend more money to buy a compatible keyboard and mouse, which will cost more than you were prepared to spend. Therefore, my advice is to buy the bundled offer, which works out cheaper in the end.

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