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Topic: 2 Axis Solar Tracker (The evolution of an idea) (Read 16 times) previous topic - next topic

dsmith5167

#5
Aug 05, 2012, 06:56 pm Last Edit: Aug 05, 2012, 07:41 pm by dsmith5167 Reason: 1

Don't forget diodes across the relays.
Missing 0.1uF caps from pins 7, 20, 21 to  Gnd.


I updated the original schematic at the top of the thread per your suggestions.

I used 1N4007 diodes as I have them on hand.
A good choice? or is there something better?
What parameters qualifies as better?
I am thinking low leakage high breakdown voltage ratings.

Curious:
There is no circuitry after the coil (it goes directly to ground) and as I have it shown now any spikes can feed back to the microcontroller.
It would make more sense to me to have the diodes in-line with the controller pins blocking any return voltage.
Is the Newbie looking at this the right way?


Quote

Protection diodes for relays
Transistors and ICs must be protected from the brief high voltage produced when a relay coil is switched off.
The diagram shows how a signal diode (eg 1N4148) is connected 'backwards' across the relay coil to provide this protection.
http://www.kpsec.freeuk.com/components/relay.htm



Also I added the .1uF (100nF) cap across the 7, 20, 21 node.
I notice you used the word "caps" (plural) in your post.
Do you recommend 3 (one for each pin)?

Your comments and thoughts are greatly appreciated.
Thanks

dsmith5167


You might want to provide a rechargeable battery.  If the tracker follows the sun until sunset it will be in just the wrong position to power the motors at sunrise.  With no power it will have to wait until it gets enough energy from the reflected sunrise light to move the array back to the sunrise position.


:*...
I forgot to mention that in the write up, but you are correct.
I have an old cordless wall phone that I am going to scavenge the rechargeable battery out of (possibly circuitry also).
It is only 3.6v so I will have to expirement to see if it will be big enough to trip the relay and drive the assembly.


The linear regulator wastes some of that precious solar energy.  A DC-to-DC converter would be more efficient.


Any recommendations or links to an appropriate converter?

I was also thinking of replacing the photoresistor circuit(s) with plain LED's to improve efficiency.
I wouldn't have to power them as they work like mini solar cells (light in - electrons out).
It would also reduce part count and cost.

Thanks for the input.

CrossRoads

Yes, cap on each pin: Vcc, AVcc, Aref. Aref is cap only, do not connect to 5V.

Here are three ways to drive a relay coil.  Keep the inductor spike off the arduino pin.
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

pito

#8
Aug 07, 2012, 02:42 am Last Edit: Aug 07, 2012, 02:44 am by pito Reason: 1
1. mind the total current through 328p when all relays on, better use the transistors for switching the relays.
2. I would not use the tracking with those optical homing sensors - add simply an RTC and you can calculate the SUN's position with GREAT precision even at night :)
p.

dsmith5167


1. mind the total current through 328p when all relays on, better use the transistors for switching the relays.
2. I would not use the tracking with those optical homing sensors - add simply an RTC and you can calculate the SUN's position with GREAT precision even at night :)
p.


As the software is programmed now only 1 relay will ever be on at any given time.
But I will be measuring the current through the relay just for curiosity now.  ;)

RTC (Real Time Clock?)
Incorporating a clock into the system will add a layer of complexity I am not familiar with at this time.
It may be a better alternative/solution but I don't have that knowledge in my tool bag.
The three photoresistors, as I originally configured them, were more accurate than was necessary.
I would also think that using an absolute type of positioning system would mean I have to position the system in a particular manner at a particular time.

If you have a good example of using the RTC in a solar tracker I would like to look at it.

Your post also made me realize the photoresistors are probably sensitive enough to track the moon.
Possibly wasting energy throughout the night. Hmmmm :~

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