# Heliotropic tracker

Started by March 25, 2016
```Say I have (for example) a cellphone charger that uses sunlight to charge
the phone. The phone and charger are in an attic room with one small roof
window so as the sun moves around the sky, the small patch of sunlight
slowly creeps from one side of the floor to the other. How could one best
implement a mechanism to track the sun's movement and keep that charger
in the sunny patch at all times? - (assuming the tracking 'vehicle' has
it's own power supply so requires nothing from the solar cell's output.)
```
```On 3/25/2016 7:54 PM, Chris wrote:
> Say I have (for example) a cellphone charger that uses sunlight to charge
> the phone. The phone and charger are in an attic room with one small roof
> window so as the sun moves around the sky, the small patch of sunlight
> slowly creeps from one side of the floor to the other. How could one best
> implement a mechanism to track the sun's movement and keep that charger
> in the sunny patch at all times? - (assuming the tracking 'vehicle' has
> it's own power supply so requires nothing from the solar cell's output.)
>

That's a good question, Chris. Who will judge the responses for the best
implementation?
```
```On Saturday, March 26, 2016 at 11:57:17 AM UTC+11, Chris wrote:
> Say I have (for example) a cellphone charger that uses sunlight to charge
> the phone. The phone and charger are in an attic room with one small roof
> window so as the sun moves around the sky, the small patch of sunlight
> slowly creeps from one side of the floor to the other. How could one best
> implement a mechanism to track the sun's movement and keep that charger
> in the sunny patch at all times? - (assuming the tracking 'vehicle' has
> it's own power supply so requires nothing from the solar cell's output.)

Stick a ladder up against the window, and put the charger close enough to the window that it's always in sunlight.

--
Bill Sloman, Sydney
```
```On Friday, March 25, 2016 at 5:57:17 PM UTC-7, Chris wrote:
> Say I have (for example) a cellphone charger that uses sunlight to charge
> the phone. The phone and charger are in an attic room with one small roof
> window so as the sun moves around the sky, the small patch of sunlight
> slowly creeps from one side of the floor to the other. How could one best
> implement a mechanism to track the sun's movement and keep that charger
> in the sunny patch at all times? - (assuming the tracking 'vehicle' has
> it's own power supply so requires nothing from the solar cell's output.)

1. Obtain a large potted sunflower. Place flower in proximity to window. Affix the solar panel bit of the charger to the flower, active surface outward.

2. Hire a small child to keep the panel aimed directly at the sun through the window.

3. Duct-tape the panel directly to the window.

Mark L. Fergerson
```
```On 3/25/2016 10:19 PM, bill.sloman@ieee.org wrote:
> On Saturday, March 26, 2016 at 11:57:17 AM UTC+11, Chris wrote:
>> Say I have (for example) a cellphone charger that uses sunlight to
>> charge the phone. The phone and charger are in an attic room with
>> one small roof window so as the sun moves around the sky, the small
>> patch of sunlight slowly creeps from one side of the floor to the
>> other. How could one best implement a mechanism to track the sun's
>> movement and keep that charger in the sunny patch at all times? -
>> (assuming the tracking 'vehicle' has it's own power supply so
>> requires nothing from the solar cell's output.)
>
> Stick a ladder up against the window, and put the charger close
> enough to the window that it's always in sunlight.

That's a good answer, Bill, and one that I considered. However, I think
Chris is the poster that wants a direct answer to his question rather
than alternate solutions.
```
```On 3/25/2016 5:54 PM, Chris wrote:
> Say I have (for example) a cellphone charger that uses sunlight to charge
> the phone. The phone and charger are in an attic room with one small roof
> window so as the sun moves around the sky, the small patch of sunlight
> slowly creeps from one side of the floor to the other. How could one best
> implement a mechanism to track the sun's movement and keep that charger
> in the sunny patch at all times? - (assuming the tracking 'vehicle' has
> it's own power supply so requires nothing from the solar cell's output.)

For a given latitude and time of year, the sweet spot will move in
a predefined course across the floor.

Anything that can move (or be moved) carrying the targeted charger
can monitor the output of the solar cell (over times longer than
any "local disturbances") and advance as long as output climbs,
stopping once the output starts to fall (waiting for the sweet spot
to catch up to it).

At end of day, manually reposition device at start of the next day's
trek.

```
```On Sat, 26 Mar 2016 01:19:53 -0500, John S wrote:

> That's a good answer, Bill, and one that I considered. However, I think
> Chris is the poster that wants a direct answer to his question rather
> than alternate solutions.

Assuming this is some sort of abstract, mind-experiment type question,
isn't this something that could most readily be implemented with a
software solution? Say you surround the main charging cell with four
smaller satellite cells. You then mount the phone, charger and satellite
cells to a small model car controlled by, for example, a Raspberry Pi
which compares the output levels from the satellite cells. You could then
come up with a fairly simple algorithm instructing the car to move so as
to always be in the spot of maximum light.
But there's probably a really ingenious, totally analog, old-school
alternative of doing it better and more simply that I'm unable to think
of right now.

```
```On 3/25/2016 7:54 PM, Chris wrote:
> Say I have (for example) a cellphone charger that uses sunlight to charge
> the phone. The phone and charger are in an attic room with one small roof
> window so as the sun moves around the sky, the small patch of sunlight
> slowly creeps from one side of the floor to the other. How could one best
> implement a mechanism to track the sun's movement and keep that charger
> in the sunny patch at all times? - (assuming the tracking 'vehicle' has
> it's own power supply so requires nothing from the solar cell's output.)
>

I don't have an answer, but I think this is a well thought out, simple,
simple, solar tracker. Pretty coll!

Mikek

```
```On Sat, 26 Mar 2016 11:41:36 +0000, Cursitor Doom wrote:

> But there's probably a really ingenious, totally analog, old-school
> alternative of doing it better and more simply that I'm unable to think
> of right now.

Actually there *is* a simpler solution, Chris. Mark the positions on the
floor of the extent of the light patch at dawn and dusk then join 'em up.
You now know the arc the light patch will traverse during the day. You
also know in which direction it will pass with 100% certainty, so there's
no need for 'satellite' cells at all. Just one light dependent resistor
on the trailing edge of the 'vehicle' you're using. Arrange things so
when that LDR falls into shadow, the wheels get a momentary blip of
power; just enough to move them say one revolution or two inches across
the floor back into the light zone again.
Sorted! :-)

```
```"Cursitor Doom" <curd@notformail.com> wrote in message
news:nd6939\$d56\$2@dont-email.me...
> Actually there *is* a simpler solution, Chris. Mark the positions on the
> floor of the extent of the light patch at dawn and dusk then join 'em up.
> You now know the arc the light patch will traverse during the day. You
> also know in which direction it will pass with 100% certainty, so there's
> no need for 'satellite' cells at all. Just one light dependent resistor
> on the trailing edge of the 'vehicle' you're using. Arrange things so
> when that LDR falls into shadow, the wheels get a momentary blip of
> power; just enough to move them say one revolution or two inches across
> the floor back into the light zone again.
> Sorted! :-)

Needs a reset circuit every morning, too, but otherwise works.

The track needs to be adjusted every month or three, though.

Exercise: show why this is true. :-)

Bonus exercise: solve this problem with the RC car and an analog circuit.
too. :^)

Tim

--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design
Website: http://seventransistorlabs.com

```