# need HELP on dual axis solar tracker

#### kevinng

Joined Jul 18, 2011
9
Hi everyone, please help me, Im an electrical engineering student, I need to build a dual axis solar tracker within a weeks. I need to build it to turn horizontally and vertically, the sensors will track the sun then the NE555 will be the servo controller. I plan to use the components as shown below :

1. Servo Motor
2. NE555 IC
3. 4 LDR
4. belt
5. solar panel
6. resistors and capacitors

but I have no idea how to connect all of these together, I search some information on google, but there's no circuit that match with what i want.. Can anyone just please help me to connect all of these together?

actually, what's the different of DC servo and servo??
by using NE555 IC, i need to make it to astable so that it can control the servo, right?

is this the astable control circuit?

The last page of this PDF file, is it just that simple to build the control to the servo??
file:///C:/Documents%20and%20Settings/User/Desktop/Destop/final%20year%20project/circuit/erii5_555_timer_astable_operation.pdf

#### wayneh

Joined Sep 9, 2010
16,556
Just one motor, but both axes? Could be tricky. You know that if you point one axis at the north pole, the panel will revolve only about that one axis during a day (like a telescope on an equatorial mount)? You could adjust that axis as infrequently as once a week and still have good accuracy.

One challenge is how to arrange the LDR sensors so that their signals can be translated into a useful instruction. Are you not allowed to use transistors?

#### kevinng

Joined Jul 18, 2011
9
sorry, it should be 2 motors. No, I can use what ever that I manage to get, as long as I can show the tracking system.

#### wayneh

Joined Sep 9, 2010
16,556
Search this forum for "solar tracking" or whatever other keywords you can think of. I know I've seen a lot here on the topic.

#### John P

Joined Oct 14, 2008
1,864
Do you really want to use a hobby servo? They're designed to move a light load quickly. If your solar panels have any mass to them, the servo won't be able to move the unit, and you'll have a hard time making a mechanical structure that links the two together; especially as you plan to have 2 axes.

But if there aren't any solar cells, just sensors, then it should be OK, but the motion will be fast and jerky.

But I'm not sure that this is a job for a servo of that kind anyway. If you have an off-centered location relative to the sun, wouldn't you want to run a motor until you've centered it again? What a hobby servo would do is to run the output to a particular location depending on the electrical input--it wouldn't be "correcting an error" by re-centering the sensors. I think what you really want is a pair of small motors with a large gear ratio, and simply an amplifier that drives forward or reverse until the sun is seen to be on center. That would in fact be a "servomechanism" in the classic sense.

#### wayneh

Joined Sep 9, 2010
16,556
Yeah, just for comparison, a telescope drive is simply a clock giving one complete revolution every 24 hrs. The fact that you need 360° in 24 hrs allows you to pre-program that into a mechanical system, and use the sensors as just a way to make minor corrections.

#### Kermit2

Joined Feb 5, 2010
4,162

#### kevinng

Joined Jul 18, 2011
9
i searched on the internet, on the internet, they said NE555 is not very suitable for applying on solar tracker. well, i really have no idea about what component should i really use..
so, servo motor is not suitable, then what about stepper motor? if im going to use stepper motor, then what control system should i build?

#### kevinng

Joined Jul 18, 2011
9

#### wayneh

Joined Sep 9, 2010
16,556
That first link is too small to really tell, although it's using transistors to turn a motor on and off.

#### kevinng

Joined Jul 18, 2011
9
can i build a solar tracker by using 555?
what circuit of 555 should i use?
what is the use of H-bridge?
i really have no idea what should i consider for building a dual-axis solar tracker

#### Bernard

Joined Aug 7, 2008
5,720
A simple solar tracker can be made with a LDR & 555. Use 555 as a one shot timed to advance panel about 5 degrees for each activation. Shade the east side of the LDR so that the LDR is illuminated when the sun is about 3 deg. before virtical to panel. LDR is connected from gnd. to pin 2 with a resistor from pin 2 to + supply. Will need additional circuitry to return to starting point & compinsate for clouds, maybe another 555 to advance panel if no signal is received from first 555 within a given time.
Depending on size of panel a " Powerfull 12VDC Gearhead Motor" SN: G18213 from The Electronic Goldmine, about 38 in oz torque. That is what i'm planning to do with mine & a 15 W panel- one axis to start.

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#### kevinng

Joined Jul 18, 2011
9
well, I`m not really understand.
u mean that by using a 555 timer and a resistor is able to drive a motor?
well, actually i just need a driver which can drive a servo motor, as my purpose is to track the sun which does not required fast rotational speed.
how can I manage to do it?

#### wayneh

Joined Sep 9, 2010
16,556
Weight and size of panel
Available power source
Cost, time and other constraints
Required accuracy
Many more I haven't thought of.

You can make a solar tracker using several strategies. I suggest you block out your goals and a tentative strategy. Folks here can then help you tackle each part, and develop a plan. Starting with a parts list and no plan is ... no plan.

#### Bernard

Joined Aug 7, 2008
5,720
Yes. LDR 1kΩ 36 in from 60W lamp. In test, covered LDR with 4 layres of semi opaque film to give about 4kΩs in direct sun. Used 27kΩ in series & 5V supply; in sun trigger V was .8V, slightly shaded- 2.5V. trigger V about 1.7V. 555 drives referenced motor just fine @ 5V & 15mA. It is a servo motor when used with feed back control as it is.

#### kevinng

Joined Jul 18, 2011
9
I understand that, thank you.

Well, I need to build a solar tracker which can track both vertical and horizontal axis according to the sun path, so I will need a high torque low speed motor which I decided to use a RC hobby servo motor.

The idea is like this, two LDRs will connect to a NE555 timer to trigger the RC servo motor to turn until the position that desired. The LDRs will be place separably with a block in between them, when there's differences in resistance, LDRs will send signal to NE555 timer, the timer will then send signal to trigger the servo motor. Motor will stop when both LDRs resistance are the same.

I plan to build two circuits, one of it will control the vertical axis and another controls the horizontal axis.

I need a circuit with NE555 timer to send signal to a RC hobby servo motor as shown in the previous figure. (it will be great if there's any other simple circuits available for servo)

by using this circuit, can the servo motor rotates until the desire position and stop and wait for the next trigger? or any additional circuit is needed?

Now the problem is I have no idea where should I connect the LDRs in the circuit, and I have no idea can the servo stop at the desire position after the signal is cut off.

I did some google on this, but I can't find a circuit that could control the servo motor like what I need.

Weight of the solar panel and any other parts will not be the priority consideration as I just need a circuit that could trigger the motor to a desire position and stop there with LDRs and a control circuit.

thank you

#### kubeek

Joined Sep 20, 2005
5,736
You could use a pair of LDRs for each axis, place some plastic plane between them. Then use simple logic to activate the motor, i.e. rotate left when the right LDR is shaded, and stop when both have light. If both are shaded don´t do anything.
Ditto for the other axis.

This should be pretty easy to implement, after that you will have to look onto the motor. For this kind of tracking a simple geared DC motor would be better than a servo, because servo would require more complex circuit to operate.

If the panel is larger, you could try using a pair of screen wiper motors. At least the one I have is worm-geared so it won´t change position when off even for heavy loads.

#### kevinng

Joined Jul 18, 2011
9
yes, that is what I want.

but the problem is, how should I connect the LDRs to the NE555 and to the geared DC motor?

#### kevinng

Joined Jul 18, 2011
9
You could use a pair of LDRs for each axis, place some plastic plane between them. Then use simple logic to activate the motor, i.e. rotate left when the right LDR is shaded, and stop when both have light. If both are shaded don´t do anything.
Ditto for the other axis.

This should be pretty easy to implement, after that you will have to look onto the motor. For this kind of tracking a simple geared DC motor would be better than a servo, because servo would require more complex circuit to operate.

If the panel is larger, you could try using a pair of screen wiper motors. At least the one I have is worm-geared so it won´t change position when off even for heavy loads.
Like what u said, do nothing when both LDR have light.
so is it possible that when both LDR have light, then the NE555 will send a suitable signal to togger the DC motor to the desire position?

#### Bernard

Joined Aug 7, 2008
5,720
On paper a hobby servo will work; need to supply a fixed frequency voltage controller PWM signal with { estimates ] 35% duty cyclr for full left & 65% for full right, & maximum 180 deg. rotation. With a real gear head motor turning at 20 RPM, an additional 300:1 reduction is needed for
for panel rotation of 2.5 deg/min. So a small motor [ 3V @ 14mA ] can produce about 28 pound- feet of torque. Maybe a pair of LDRs feeding a comparator, with some hesteresis added, & an invertor could feed each side of an H bridge, low power- 2n3904's & 2n3906's, to control the motor.
another set to control the other axis.
P.S.-i've never used a hobby servo- started a radio controlled project in 1960- vacuum tubes, but a move came along.