Wednesday, 2 October 2013

A Power Supply & Self Powered USB Hub for Raspberry Pi

This is another of those, "this is so simple and so clever, why didn't i think of it" moments.
Like many of us Bharath Bhushan was slightly miffed at the fact that you need separate supplies for a raspberry Pi and its peripherals.
His solution was both simple and elegant. He simply chopped open his USB hub, and tapped off a power feed to go directly to his Pi.
I like the clever way he cut his existing USB cable, the yellow one in the photo, using one end for the power supply and the other to extended the hub so it could more easily reach the Pi.
For an detailed explanation and full construction details go to http://bharath.lohray.com/weblog/a-power-supply-self-powered-usb-hub-for-raspberry-pi/#.UkwOQFOnepF
[Via Make]

Unfortunately the USB hub I was using did not seem to have a separate supply regulator and so the raw 9V goes straight into a large blob on the PCB.
Its going to be a bit of a gamble if your hub is suitable, and I don't think you can easily check before buying as I can't see the people in PCB World being terribly understanding if you start taking their kit apart in the middle of the shop.
My hub was glued together, you can't just unscrew it, so I had to carefully cut round the seam with a craft knife and then gently lever it apart. Its very easy in this situation to (a) cut yourself (b) cut into the circuitry inside.
If possible hold the Hub in place with a clamp so it doesn't shift, which makes it much easier to work on accurately, and wear gloves.
Once you start to cut through it is normally possibly to gently prize it apart, slowly, without extra cutting, although you might have to work on the case to get it back together again.

Make: Visualize Your Heartbeat With This Homemade Pulse Sensor

Here is a clever little project from those awfully nice people over at the make website.
It s a front end sensor for measuring your pulse rate with an arduino, raspberry pi or any other board with GPIO access.
The principle is simple, illuminate the inside of your thumb with an LED, and measure how much light comes back. It works because there is an artery in your thumb that reflects back some of the light, but as the blood pulses the diameter of the artery increases so it reflects more light.
The Op-Amp circuit detects these changes in light level, amplifies them and passes then as a clean digital signal onto the processor board.
The whole thing can easily be built on vero-board or some other pre-printed generic PCB, although in practice if you were just making it out of curiosity I can't see any reason why it wouldn't work on a breadboard.
It only uses readily available components, although its not clear why they use a quad op-amp and then don't use half the circuit, perhaps it was just the way their PCB was made. Personally I would try a dual op-amp to save space and few pence.
For full details, and a video,  go to http://makezine.com/video/visualize-your-heartbeat-with-this-homemade-pulse-sensor/