# Need help to light up 8 LEDs with different color

#### jenovauh

Joined Jul 4, 2013
246
I'll try one more time to understand what your constraints are.

If you are limited to six solar cells that produce a maximum of 2V at 150mA each, and you want to recharge the batteries using only those cells, then you must not draw more power from the batteries than the cells can produce. In the best case (bright sun, best angle), those six cells will produce 1.8 watts. Realistically, they probably will not average more than one watt output during daylight hours. So, you have only one watt that you can draw from your batteries if you expect the solar cells to recharge the batteries.

Next, if you are limited to two 1.2V batteries, then you can connect them either in parallel, in which case you have 1.2V, or in series, in which case you have 2.4V. Thus, the only LEDs which you could light would be those with less than 2.4V drop, i.e., the red (1.8 - 2.3V) and the IR (1.5 - 1.5V), and that would be with the batteries in series. Without some voltage boost circuit, it would be impossible to light the blue or the UV.

So, you don't have enough voltage from the batteries to light the LEDs, and you don't have enough current from the solar cells to recharge the batteries. Therefore, you must have more batteries and more solar cells in order to light all the LEDs you have listed to full brightness.

What options will you consider? More batteries, more solar cells, or fewer LEDs?
Thanks for understanding me and I would say increase the number of batteries. Will a 9V rechargeable battery be okay? Also If increasing the number of solar cell and remain the 2 x 1.2V battery, how many pieces do I need? I am opening to any options except the 3 main points which I need to achieve.

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#### tracecom

Joined Apr 16, 2010
3,944
Just a few thoughts: If Blue could be dimmed a bit to 60 mA, could put 2 Blue & IR in one string; 1 Red & 1 UV for second string; 3 Red for 3rd string. Suggest Vcc of about 10 V. The drain on 3 parallel strings is about 1 W. If Vcc derived from 2 AA Ni-MH running for 8 hours would try to draw about 5 Ah,; need bigger batteries or more in series.
Picking up on Bernard's suggestion, you could get by with a 9V supply, in which case the blue/IR string would be running at 60mA with a 3.6Ω resistor, the red/UV string would be running at 20 mA with a 150Ω resistor, and the red only string would be running at 20mA with a 110Ω resistor. That would total 100mA of current at 9V, or .9 watts.

In order to charge a 9V battery, you would need about 12V from your solar cells, which would mean you need to either add two more cells like the two you have, or buy a new cell that is rated for 12V out at 200mA or more.

Why have you chosen blue LEDs that draw so much current? Will you be satisfied to run them at 60mA instead of their rated 100mA? And what are the specifications of the 9V battery you plan to use?

#### jenovauh

Joined Jul 4, 2013
246
Picking up on Bernard's suggestion, you could get by with a 9V supply, in which case the blue/IR string would be running at 60mA with a 3.6Ω resistor, the red/UV string would be running at 20 mA with a 150Ω resistor, and the red only string would be running at 20mA with a 110Ω resistor. That would total 100mA of current at 9V, or .9 watts.

In order to charge a 9V battery, you would need about 12V from your solar cells, which would mean you need to either add two more cells like the two you have, or buy a new cell that is rated for 12V out at 200mA or more.

Why have you chosen blue LEDs that draw so much current? Will you be satisfied to run them at 60mA instead of their rated 100mA? And what are the specifications of the 9V battery you plan to use?
The blue LEDs I bought is a 8mm straw hat, have not got delivered to me yet. So I am not sure how bright or dim it will be to run at 60mA. And as for the 9V battery I am thinking of getting one that have 300mAh. Would that be enough? Or maybe I can series 4 X 1.2v battery to make it work as well?

Base on all the information you guys had advised. Can I use that 555 circuit to start off with what I need or need to figure out a design for my need?

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#### tracecom

Joined Apr 16, 2010
3,944
The blue LEDs I bought is a 8mm straw hat, have not got delivered to me yet. So I am not sure how bright or dim it will be to run at 60mA. And as for the 9V battery I am thinking of getting one that have 300mAh. Would that be enough? Or maybe I can series 4 X 1.2v battery to make it work as well?

Base on all the information you guys had advised. Can I use that 555 circuit to start off with what I need or need to figure out a design for my need?
I see no reason to use a CMOS 555. I would use an NE555, which will be able to run on 9V and supply the 100mA for the LEDs. You simply want to turn all the LEDs on when there is light and off when it is dark. No flashing required, right?

My suggestion would be to get your LEDs, test them at the current stated and in the strings as described, and using the battery you plan. When that works the way you want it, building a 555 circuit to switch them on and off will be fairly straight forward. The last step will be to design a solar charger for the battery.

#### jenovauh

Joined Jul 4, 2013
246
I see no reason to use a CMOS 555. I would use an NE555, which will be able to run on 9V and supply the 100mA for the LEDs. You simply want to turn all the LEDs on when there is light and off when it is dark. No flashing required, right?

My suggestion would be to get your LEDs, test them at the current stated and in the strings as described, and using the battery you plan. When that works the way you want it, building a 555 circuit to switch them on and off will be fairly straight forward. The last step will be to design a solar charger for the battery.
Yes i agree, I want to replace that CMOS 555 to NE555 which I already had, I will try to figure out if they work on that circuit. For the turn on day time and off at night time and recharging are you able to roughly tell me how I can change that circuit to work the way I wanted and what other component do I need? Thanks a lot.

#### tracecom

Joined Apr 16, 2010
3,944
Here is a circuit I tested that would work. Instead of a 555, it uses an op-amp and a MOSFET. Most N-channel MOSFETs will work in this circuit, but a logic-level MOSFET (like the IRLZ44N) would be best with a 9V supply. Look at the schematic and the notes to understand how the op-amp responds to changes in light falling on the LDR and then switches the op-amp, which controls the DC load attached to the MOSFET.

Also have a look at this thread to see an LDR (also called a CDS) used to trigger a 555. http://forum.allaboutcircuits.com/showthread.php?t=86877

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#### jenovauh

Joined Jul 4, 2013
246
Here is a circuit I tested that would work. Instead of a 555, it uses an op-amp and a MOSFET. Most N-channel MOSFETs will work in this circuit, but a logic-level MOSFET (like the IRLZ44N) would be best with a 9V supply. Look at the schematic and the notes to understand how the op-amp responds to changes in light falling on the LDR and then switches the op-amp, which controls the DC load attached to the MOSFET.

Also have a look at this thread to see an LDR (also called a CDS) used to trigger a 555. http://forum.allaboutcircuits.com/showthread.php?t=86877
Thanks again tracecom, I will read on that and understand first. And I do not have those part to test. Time to purchase.

#### jenovauh

Joined Jul 4, 2013
246
Here is a circuit I tested that would work. Instead of a 555, it uses an op-amp and a MOSFET. Most N-channel MOSFETs will work in this circuit, but a logic-level MOSFET (like the IRLZ44N) would be best with a 9V supply. Look at the schematic and the notes to understand how the op-amp responds to changes in light falling on the LDR and then switches the op-amp, which controls the DC load attached to the MOSFET.

Also have a look at this thread to see an LDR (also called a CDS) used to trigger a 555. http://forum.allaboutcircuits.com/showthread.php?t=86877

I suppose to VR1 in the circuit is a voltage regulator, can I know exactly which part number I can use? I have never use one before. And also the LM741CM when I try to find the part I am only able to find LM741 and LM741CN. Are they correct part number?

#### tracecom

Joined Apr 16, 2010
3,944
I suppose to VR1 in the circuit is a voltage regulator, can I know exactly which part number I can use? I have never use one before. And also the LM741CM when I try to find the part I am only able to find LM741 and LM741CN. Are they correct part number?
VR1 is a variable resistor, better known as a potentiometer, or "pot." It is used to set the amount of light that switches the op-amp. LM741CM is my typographical mistake; it should be LM741CN, LM741C, or just LM741. The LM741 is a very old op-amp, but still does a good job in some applications.

Also, the IRLZ44N is a high current N-channel MOSFET that can be controlled by a low voltage at its gate. It will work in your application, but so would other (smaller) N-channel logic level MOSFETs such as the BS170.

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#### jenovauh

Joined Jul 4, 2013
246
VR1 is a variable resistor, better known as a potentiometer, or "pot." It is used to set the amount of light that switches the op-amp. LM741CM is my typographical mistake; it should be LM741CN, LM741C, or just LM741. The LM741 is a very old op-amp, but still does a good job in some applications.

Also, the IRLZ44N is a high current N-channel MOSFET that can be controlled by a low voltage at its gate. It will work in your application, but so would other (smaller) N-channel logic level MOSFETs such as the BS170.
Understood, I know what is pot. I will try to get those parts and try with them. Thanks again for the explanation.

#### tracecom

Joined Apr 16, 2010
3,944
Here is a new schematic. It shows the correct connections for turning the power on when there is light on the LDR. It also shows the use of a BS170 MOSFET, which is a better choice for your power levels than the IRLZ44N.

I have breadboarded the circuit as shown in this post, and it works well. I can post a photo of my breadboard if you want to see it.

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#### jenovauh

Joined Jul 4, 2013
246
Here is a new schematic. It shows the correct connections for turning the power on when there is light on the LDR. It also shows the use of a BS170 MOSFET, which is a better choice for your power levels than the IRLZ44N.

I have breadboarded the circuit as shown in this post, and it works well. I can post a photo of my breadboard if you want to see it.
Oh thank you so much. I had just finished looking online for all the parts and ordered them, including the IRLZ44N lol. Never mind I will go and buy the BS170 now. Excited to try on the circuit. Sure I would like to see your breadboard layout, I always feel that the way I layout my component, looks super messy. Need to learn the right method from you.

#### tracecom

Joined Apr 16, 2010
3,944
Here is a photo of my solderless breadboard. Notice that I put one blue LED on the output of the BS170 MOSFET to test the circuit. And in the photo, you can see that the blue LED is lit because of the flash on the camera, so the response is quite fast.

All black wires are ground, and all red wires are Vcc. All resistors are .25w. I didn't label the components, but you can probably figure out which is which. If you have questions, just ask.

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#### Bernard

Joined Aug 7, 2008
5,720
jenovauh, did you measure some of the solar cell for open ckt V, & short ckt. current?

#### tracecom

Joined Apr 16, 2010
3,944
jenovauh, did you measure some of the solar cell for open ckt V, & short ckt. current?
Bernard,

I hope when we get to the battery charger you are here. I have never built one.

#### jenovauh

Joined Jul 4, 2013
246
Here is a photo of my solderless breadboard. Notice that I put one blue LED on the output of the BS170 MOSFET to test the circuit. And in the photo, you can see that the blue LED is lit because of the flash on the camera, so the response is quite fast.

All black wires are ground, and all red wires are Vcc. All resistors are .25w. I didn't label the components, but you can probably figure out which is which. If you have questions, just ask.
Thank tracemon, guess those part I order should arrive in 1-2 week time before I can start the project. Meanwhile I will read and understand how they work.

#### jenovauh

Joined Jul 4, 2013
246
jenovauh, did you measure some of the solar cell for open ckt V, & short ckt. current?
Hi Bernard, I do not know what you mean by open ckt V & short ckt current. Sorry I do not know the term and can you explain to me? I only know the solar cell is 2V 150mA, how can I check on the details you need for the solar cell?

#### Bernard

Joined Aug 7, 2008
5,720
Open circuit voltage means measuring the cell voltage in sun light without a load; short circuit current is measured by setting meter on high mA, 200 mA or higher & connecting leads directly to cell. If your cells are 2V OC, under load it will drop to about 1.4V.

#### jenovauh

Joined Jul 4, 2013
246
Open circuit voltage means measuring the cell voltage in sun light without a load; short circuit current is measured by setting meter on high mA, 200 mA or higher & connecting leads directly to cell. If your cells are 2V OC, under load it will drop to about 1.4V.
Thank and I will do a test for that on this coming weekend.