Solar tracking sundial

In my previous project Electrical Sundial I was testing how cheap solar panels may be used to sense sun's position. A surprisingly good accuracy, ±30sec, was then achieved if only the sky was reasonably clear. Instead, in a cloudy weather the accuracy decreaced dramatically, which is why I started this new project. Its first results are shown below.

First time in outdoors

Note the instrument's hour and minute hands and the wheel showing seconds. Of course they can not be very accurate but it will be interesting to see, how often the electronics is trying to correct the position.

The driving frequency of the motor, about 10 times in a minute, was observed.
See a video.

Schematics of the position sensor

The sensor is from my old electric sundial but here the panels E and W are only used.

Solar tracker circuit drawing

Voltage comparator LT1017 compares the energy output of the solar panels E and W and drives the Lego motor accordingly. Motor's drive current is about 40 mA but in the start it needs over 100 mA. That it gets through the switching transistor BC558 which has a low saturation voltage. This is needed as the power source, two solar garden lights, produces only +2.6V. The electronics drives the motor only forward. A manual switch is used to drive it backwards if needed.

Carden light opened

Inside the garden lights there are plenty of room for the electronics.

The driving mechanism was built from old children toys. As a time dial serves a small table clock. Some Lego parts were used to clutch it into a 24 teeth worm gear which again was made of some BILO parts. Between the motor and the worm gear there is still a 1:3 gear and a 1:20 Lego gearbox.

   Sun tracking test, time comparisons.
In 100 seconds the tracking motor corrected the position about 20 times. When compared to a digital timepiece, the tracker followed the sun with an accuracy of about ±6 sec. That is the accuracy, which a mechanically perfect instrument could possibly achieve. With my toy-instrument the long term accuracy seems to be about ±3 min only or even less, maybe.

From my part, I think, this project is now at the end. Its idea clearly works but I have started a new project   (a real schoolboy science woodoo project ;)  and I will need my solar tracker there. I am curious to know, how much carbon dioxide is needed to produce a maximum greenhouse effect. I am aware that many scientist already believe they theoretically know the answer but, I will try to verify the matter also experimentally now.

You should never say a project is at the end. At least I have made again some modifications to the tracker. It now has more stronger gearbox and a more efficient photocell to drive the motor. In addition, the seconds wheel is removed and the motor drives directly the seconds gear of an ordinary clock. Sensor panel S, which was earlier unused, is now used to monitor the sky brightness and it halts the operation, if the sun is behind a cloud. See the pictures and the video below.


Following programs were intensively used in this project:
MAXCLOCK for solar time calculations,
Pc-Calculator for general calculation.
Last edited 02.09.2012
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