Posted by: Claudio Carbone | 17 July 2011

Finally something techy!

Hi guys!

Finally I can write about something really related to technology and stuff.
A couple weeks ago, I was searching for a Bluetooth embedded module that supported HID (Human Interface Device), a protocol widespread in all ambients (Windows, Mac, Linux) to support many kinds of peripherals: from mice and keyboards to complex custom acquisition cards.
Sadly it hasn’t arrived yet, so I can’t show you that, but while browsing a kind of “social engineering” site called InMojo (give it a look, it’s full of interesting projects and boards!) I stumbled upon a little nifty circuit: an automatic charger/power supply designed to output power on a USB-A plug, while simultaneously charging a Lithium cell, harnessing the power of the sun

So I immediately ordered a circuit and two solar panels, and for 24$ shipped, I’d say it’s nice and cheap enough!

Solar panels just unboxed!

Now my idea of the project is to build a 2-axis sun tracker powered with two RC servomotors, everything controlled by a pic with an RTC, and powered by the very same panels with attached Inmojo circuit and a Lipo/Liion battery.
But, how to track the sun?
I figured out that a resistor bridge made of photo-resistors would do the trick.

The sun tracking module

The sun tracking module

Here you can see a board from another project with a PIC 18F4553 running at 48MHz side by side with 2/3rds of the sun tracking module.
The “M” like shape above is made of two diodes (to clamp the voltage) and two 1% resistors: these provide the reference voltage to compare to determine when the sun is aligned and when it is not.
Below that are 4 photo-resistors connected in pairs to the clamping diodes.

The basic idea is to cover this with a pin-hole like dark room made of black cardboard.
When this is exposed to light, a circular lighted area is projected on the inside, following the geometrical line connecting the hole and the sun. So putting these 4 sensors below the pin-hole, the only condition in which the different sensors would read the same light value would be with the sun straight ahead! Any misalignment yields an imbalance in the center-tap voltage. This then is used by the pic to drive the motors.

Sun tracking module detail

Sun tracking module detail

I’m still far from showing anything more meaningfull then this, but hopefully in the coming weeks I’ll be able to show some more work in progress.




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