Pink Fire Pointer October 2006

Ping-Pong CD Solar Concentrator

Look at the title of this post, understood anything? The last two words are okay but got any guess whats that pingy pongy stuff. Well, let your inner curious feeling read the rest of the post to satisfy itself.

Ping-Pong CD Concentrator is an idea that flashed into my mind when I saw the shiny side of a pile of useless CDs & DVDs lying on my desktop. The ping-pong element comes from a common plastic ping pong ball thats used to play table tennis. I was a table tennis player in school.
So, imagine a CD placed on a ping pong ball with shiny side up. Ball fits into the hole in centre of CD and if you fix the ball there, what you get is a kind of rotating mirror which can rotate 2 sides either right-left or front-back. Lets visualise it;

This is what it should look like. Attach the ball to the CD using adhesive.

This rotating type of mirror-like arrangement is the precursor to our Solar Concentrator. Quite intuitively, you can see that this CD can direct light falling on it to any side wherever it rotates. This is the basic concept that is used in Heliostats (Large Sun Tracking mirrors).

Now suppose you collect some waste CDs lying around and buy an equal number of ping pong balls (very cheap) and then build individual units like described above. Arrange them on the floor and fix them there using plasticine or clay (kids play with) in such a way that all of them point toward a common centre. The image below will make things clear;

I made a demo project as you can see on the right. All the individual units are concentrating sunlight on a circular point on a wall (not in picture).

This is a nifty little idea to concentrate sunlight easily. Equate this with what is shown below;
it is a power tower with hundreds of heliostats concentrating sunlight on the top of a tower.

Like this idea? Tell us! Your Suggestions invited. More updates to this will continue.
Start collecting waste CDs now!
C ya

The Sun Tracker, Reloaded

So, finally I got some time and internet connection to update my blog after such a long time. Actually, I just joined college and moved to city, so I needed some time to settle down.

Moving on!
Remember the Sun Tracker Project I made as high school project which won me 2 national awards?
Well now I thought of working on it further and submit another project report to Indian Institute of Science (IISc) Scholarship program for undergraduate students. Earlier project report was just a plain ol' MS Word document made on a borrowed computer, but this time I had my own laptop and good knowledge of graphic designing and animation to work with. So naturally, this time it was a visual delight to go through the report. Hope that admission officers at IISc also say the same ;)

Here, I'll provide some data I collected with the working model and some illustrations showing the design, structure and circuit diagram of the model.

The basic concept on which the electronic circuit works is as shown below;

When the two oppositely placed sensors are equally exposed, the tracker is in stable state i.e. not rotating. But when one comes under shadow it signals the circuit to rotate the panel.

Actually, the 2-axis sensor looks like this;
You can see clearly the sundial kind of effect. In this image light source is at front right side of the sensor as seen by you.

Below image shows the basic schematic of the tracker design as I made it; notice the position of the sensor. A ball & socket type of joint is used which gives full freedom of rotation in two dimentions. Actually, this design, as it was later found, is not stable enough for rough applications. See for instance, in windy weather, fast moving wind will put a lot of strain on the drive belts because the torque (rotating force) on the back side of the panel due to wind would produce a lift force which would be imbalanced on the different halves of the panel.

And this is an image showing the basic, very cheap and fundamental circuit design used in a Sun Tracker. What the IC in this circuit does is to subtract the two values of voltage at oppositely placed sensors on the sensor board, here S1 & S2.
Difference of the voltages with some current amplification is what is used to drive the motor. And the motor is a basic DC type so that when the output voltage (after subtraction by IC) is positive the motor rotates clockwise and when the output is negative the motor rotates in the opposite sense.
For 2-axis rotation two of the circuits are required with 2 motors, or a single motor with a dividing gear. S3 and S4 are part of the 2nd circuit.

e-mail me for more info on this project. If you know anything about Sun Trackers please take some time to share it with me. Thanks! My e-mail address: mridul(dot)nangal(at)