Hey all I'll start by saying that I understand basic schematics and electronics jargon... took it some 20 years ago in HS so please keep that in mind.

Project is: I'm just getting back into carving small scaled diorama's, and I thought that it might be a cool idea to light one of them via a solar cell and some white LED's...

Basically I have no PCB designs and have only recently even started to price/look at parts (so I am not married to anything yet). After about a half hour of looking at parts I realized, I clearly don't recall as much as I thought I might.
Pretty much about the only restriction that have is scale (obviously). The back that I'm going to put on the project will be about 60mm square. So I was wondering if anyone could help me layout the project, and make recommendations for the parts?

No timing circuits/photo sensor or anything, just solar cell to a LED. Basically if the lights are on in the room I'd like the LED's to light.

Thanks,
~Ben~

 

Well, I think you'll need a solar cell as big as you can tolerate. 6cm square would do the job but it could be smaller, depending on ambient light.

I'd look at cannibalizing a solar garden light, because they're so cheap and would give you most of what you need. If you take out the battery and cover the CdS photocell, it'll light the LED directly from ambient light. Everyone I've played with behaves this way, but I suppose you should verify that before you tear one apart. You might need to pull the solar panel from a second one and hook it in parallel with the first, in order to get enough juice.

BTW, it's not to hard to change out the LED if you want to change color, beam width, etc. Some of the cheap garden lights don't use the best LEDs, and you can improve on them.

 

Agreed.

You could crack open a solar walkway light and you are done.

You have the charging circuit, the panel, the battery, and the LED.

Place the panel and pcb where it sees sunlight, and you should only have to extend the wires to the LED if your required destination is farther than the stock wires allow.

Here is someone who did exactly that with good results.

He used it for a door light.
Posts 20 and 24 are the main points.
http://forum.allaboutcircuits.com/showthread.php?t=46170

 

I'd look at cannibalizing a solar garden light, because they're so cheap and would give you most of what you need. If you take out the battery and cover the CdS photocell, it'll light the LED directly from ambient light.

Please pardon my ignorance here, just wanting to make sure that I am following you correctly. Take out the battery and the photocell you mean remove them from the board and replace them with a jumper wire?

 

Thanks, I had already asked Wayneh in his reply, but can I remove the battery from the board and just replace them with a jumper wire? By the looks of the schematics that were attached it looks (?) like I could but I'm not certain since it looks to me like it's using the battery to complete the circuit...
Gut reaction is that I could jump a wire between the + & - and it would complete the connection and just run from the solar cell. Please correct me if I'm wrong.

Long and short, eventually this will be placed in a curio cabinet with it's own back lighting, so a panel mounted to the back of the diorama would always be facing the light... in short I don't need the battery or photo sensor, and less parts on the board means less I have to try to hide.

http://forum.allaboutcircuits.com/attachment.php?attachmentid=25032&d=1291107099

 

Please pardon my ignorance here, just wanting to make sure that I am following you correctly. Take out the battery and the photocell you mean remove them from the board and replace them with a jumper wire?

No need to bridge the battery poles. With the battery out and your finger over the CdS photocell, these lights will light the LED when held up to a light.

Sounds like you just need the solar panel itself. These garden light are still the cheapest source that's handy. You might be able to find panels on E-bay but I'm not so sure they'll be any cheaper. Worth a look I suppose.

One thing the circuits do is provide a voltage boost. Google "joule thief" if you want to learn about that. I'm not sure this gains you anything when operated in the "special" mode you need. It's meant to allow using a single battery, and to get most of the juice out. I'd experiment with a panel connected directly to an LED, to see if it's any different than the as-is configuration.

If you find you want to keep the PCB but eliminate the CdS cell, covering it is the easiest approach. I'm not sure about eliminating the CdS cell entirely by snipping it out. Again, there's not much to lose by experimenting. Just leave yourself some leads that you can reconnect (or short together?) as needed.

 

Thanks for the idea and the clear and concise explanation...

http://www.amazon.com/gp/product/B0...&pf_rd_t=101&pf_rd_p=470938631&pf_rd_i=507846

Found these on Amazon and @ $4.00 for two, I think that I can afford to mess around with them! Can't thank you both enough.
~B~

 

Don't you know that a solar garden light needs direct summer sunlight all day long to charge its battery so it can dimmly light its LED for a couple of hours when it is dark?
The battery doesn't charge enough when it is cloudy and will be useless indoors.

The LED is so dim that it is simply an indicator at night because it can't light anything.
It also won't light up anything in daylight.

 

Don't you know that a solar garden light needs direct summer sunlight all day long to charge its battery so it can dimmly light its LED for a couple of hours when it is dark?

I'm sorry to have to disagree with you on this point, but ALL solar cells operate under the same operational principle, photons; IE: a light source. Now granted some light sources are FAR better at emitting them (such as direct summer sunlight), but it does not mean that it is required in order to get the cell to function. Think of all of the solar calculators that you've used indoors... same principle here.

It also won't light up anything in daylight.

Which is why in the earlier posts we were discussing disabling the photo sensor to "trick" the unit into thinking it was dark and lighting the LED.

 

He is not completely wrong.

These things put out very little light.

You can barely tell they are on in daylight if you jump the CdS.

Changing the LED resistor will give you more illumination for less time.

If you want this to be seen in daylight, that is something you will want to consider.

Also, just replace the stock LED with one of higher quality.

 

Now granted some light sources are FAR better at emitting them (such as direct summer sunlight), but it does not mean that it is required in order to get the cell to function. Think of all of the solar calculators that you've used indoors.

Have you ever seen a solar calculator with a power-hungry LED display? No. They use an LCD display that draws almost no current so a small solar panel is used to charge the tiny battery plus power the display and low-current Cmos chip in ordinary room light.

Many solar calculators have a photo of a solar panel instead of a real solar panel because their tiny battery lasts for years.

 

I do think at least two panels will need to be combined to get enough power for one LED from room light. The fact that the light the OP has chosen uses two AAAs is encouraging, as this means the panel may have enough voltage for the task. Many of these things just use one battery these days. Two panels together with no circuitry except the LED have a chance, IMHO.

 

Ok, I'm at least willing to accept the idea that the solar cells on the lawn lights may not put out the light that I want. Largely due to the fact that the cell itself isn't pumping the power that I need... I'm not quite willing to give up on the concept though.

Found this:
http://www.scientificsonline.com/cis-solar-panel.html

With this one as the cell (which fits the dimensions that I want) with, I'm certain, a much better power ratio than the lawn lights... and with a layout like this:

Using these LED's
http://www.superbrightleds.com/cgi-...ion=DispPage&Page2Disp=/specs/w8045_specs.htm


The idea should now work, right?

 

Unless you're anticipating full sun on your project, I doubt you'll need the current limiting resistors and I'd work on lighting a single LED, which will be plenty of light if you can get more than ~5mA through it. Did you say how much area you need to light? Maybe I'm misunderstanding your need. The panel output from ambient room light could be as little as 5% of the full sun output.

Rather than resistors to protect your LED, you might consider a zener diode, if you can find one for 3.5v or so. This will do absolutely nothing unless the panel puts out more than the reference voltage, at which point it'll break down and start conducting in the reverse direction. This will keep the panel from over-powering your LED.

 

My solar garden lights are $2.00 when on sale. I got many for free from my electrical utility company. Their solar panel is 50mm x 50mm which is only slightly smaller than the solar panel you found. It won't light an LED bright enough in room lights.

I just tested a brand new solar garden light with a fully charged battery that has much more power than a solar panel in sull sunlight. When I covered the LDR, the LED glows but won't light up anything. It is just a dot of light.

 

Unless you're anticipating full sun on your project, I doubt you'll need the current limiting resistors and I'd work on lighting a single LED, which will be plenty of light if you can get more than ~5mA through it.

Not full sun, but the panel will be aimed at a florescent light which lights the rest of the curio cabinet (it's one of the ones that has the side lights with the reflectors, and an all glass front), so the light is pretty intense.

Did you say how much area you need to light? Maybe I'm misunderstanding your need.

Well it's not so much the area, but the effect that I'm going for... Setting the scene: Think old 1970's horror flick beat up & decrepit house on a hill, car parked at the bottom the of the driveway with two people standing huddled in front of the car...
The reason that I laid out the schematic with three lights is 1 for the inside of the house to give one window a "lit" appearance. The other two would be buried in the car to make it look like the headlights are on.
And the reason for the specification on the white LED is I want the light to give it a "washed out" effect to the colors.

Rather than resistors to protect your LED, you might consider a zener diode, if you can find one for 3.5v or so. This will do absolutely nothing unless the panel puts out more than the reference voltage, at which point it'll break down and start conducting in the reverse direction. This will keep the panel from over-powering your LED.

To be honest I have never even heard of a Zener Diode, and even after your explanation and reading about it on Wiki, I'm not certain how I would put one in the circuit to use it correctly.

 

A zener is just like any diode, as far as passing current in only one direction, except for one thing: It breaks down in a predictable and useful way. Regular diodes break down also, but usually at high voltages and not so predictably.

So a zener is placed in a circuit "backwards". It does nothing useful until it breaks down. But once it starts conducting (again, in the reverse direction), it allows a varying current while holding the voltage nearly constant at the breakdown voltage. So it's a poor man's voltage regulator.

Before you get much farther, you really should experiment to find out if your "solar" power source will really work the way you want. If you need 3 lights, I'd start thinking about a wall wart. You could use any of those small, 5v mini-usb chargers. It'd give plenty of juice (typically rated 0.5-1A) and you could use those resistors to give you just the brightness you want, rock steady. That said, it sounds like you just need effects lighting as opposed to full illumination. That takes a lot less power.

 

I may have missed something, but why are you not just using a battery?

A little coin cell can light an LED nice and bright for a few hours.

If the "look" is all you are after, then do what the calculator guys do.

Run it from the battery and but the cell there as a "prop"

I also see you are unaware of solar technology.

The brown solar cells are made and filtered for INDOOR light.

The blue and black cells are not filtered for indoor light.

You HAVE to test this.

You may not achieve enough voltage to meet the LEDs Vf, or Forward voltage.

You need enough voltage to break through and turn it on, then you need current to light it.

The reason the panels in the lawn lights are there, it to produce just enough voltage to charge a cell, and just enough current to charge it in 12 to 14 hours to 70%. This will be around 5ma.

If you are hoping for a white LED, your Vf will be higher and you would need a 100w flood light to light an led.

Make the panels a prop, and light the led properly with a battery.

 

That sent me to the basement to run my own experiment. I connected a cheap, white, e-bay LED directly to one of my old solar panels. One that had no CdS cell and used 2 AAs. The solar panel is 2" square, and I disconnected it from the PCB in the garden light before connecting the LED.

As I had guessed, the LED lights under bright light, and is very bright in sunlight coming in the window. ("Very" is subjective of course, but it was too bright to look at straight on.)

I've attached 3 pictures of the panel+LED taken at the same manual exposure setting. First is ambient room light and you can just barely pick out the LED, probably nothing else. Second is with a 100w desk lamp turned partly on with its dimmer. The third shot is with it full on, 15" from the panel. The exposure setting was chosen to be underexposed under full illumination, to better show the LED. Vf was 3v under these conditions.

It's clearly possible to make this work, but the results may or may not be satisfying.

 

As I had guessed, the LED lights under bright light, and is very bright in sunlight coming in the window. ("Very" is subjective of course, but it was too bright to look at straight on.)
It's clearly possible to make this work, but the results may or may not be satisfying.

Thanks for the experiment... I kinnda thought that it was possible to do I mean I wasn't aiming at rocket science or anything! And judging by the pictures that you posted I would wind up with the "effect" lighting that I was looking for.

So my question now is if I were to add the Zener as you had suggested earlier, do I skip the resistors all together? And will I need one for each of the LEDs or just one that series into the set of LEDs?