All of the above is true, but LED brightness is not directly proportional to current. If you want 'proper' control of light output from 0 to 100% you need to use a different technique, Pulse Width Modulation, which has the benefit of not wasting energy as heat in resistors, works by turning the LEDs on full for a short time repeatedly around 50 times a second or more. Your eyes don't see the flashes, they see an average brightness proportional to the time they are switched on for. There are lots of ways to do this, I can provide a simple circuit if you want.

It depends on how the LEDs are going to be used. If he just wants to set a lower level of brightness or have then fully bright, the pot is one way to set a level.

Your point is more valid if he wished to dim the LEDs through a continuous range on demand, I agree that PWM is a better method. But it is more complicated and difficult to understand. And he may not need a continuous response.

I directly answered the TS question. If nothing else, trying the simple circuit may help him understand the difficulties. And s/he will be in a better place to understand the options

 

If using post # 37 , pots only, full power SW will short out power supply if set to max resistance.

 

I'm suggesting something like: https://www.ebay.com/itm/Mini-DC-5A...peed-Control-Switch-LED-Dimmer-D/112040803292

 

If using post # 37 , pots only, full power SW will short out power supply if set to max resistance.

Good catch! I’m embarrassed that I missed that. In light of that error, I’d remove the switch and it’s connecting wires totally. One end of the pot will provide full-on!

 

If using pots only I would stick with post # 25, # 37 not good, 10k way to high.

 

I'm suggesting something like: https://www.ebay.com/itm/Mini-DC-5A...peed-Control-Switch-LED-Dimmer-D/112040803292

Agreed, if the TS doesn't want to build something, though hard for DIY to compete on price.

 

PWM (Pulse Width Modulation) are easy to find on ebay.

KSS, I'm going to try that as well as the other solutions. I've got somePWMs, but I just ordered one closer to the ideal specs from eBay. By ideal specs I mean: 3-35VDC and 5A max. More or less what you referenced from eBay.

 

All of the above is true, but LED brightness is not directly proportional to current. If you want 'proper' control of light output from 0 to 100% you need to use a different technique, Pulse Width Modulation, which has the benefit of not wasting energy as heat in resistors, works by turning the LEDs on full for a short time repeatedly around 50 times a second or more. Your eyes don't see the flashes, they see an average brightness proportional to the time they are switched on for. There are lots of ways to do this, I can provide a simple circuit if you want.

Irving, I think I can come up with something on my own using PWM, but I can always benefit from a schematic. The PWModulator only has one pos, one neg output, right?

 

The 10 Ω resistor will not reduce the current output from the circuit, it is only there to reduce possible oscillations, at a very small reduction of output voltage.

Yea, basically the follower circuit does exactly what the name implies, that is it follows the input voltage presented to the base from the pot, set up as a divider.

(so if the base sees 2 volts the load sees 2 volts minus the loss across the transistor)

The emitter follower is a unity voltage gain circuit that has only current gain.

But, after thinking about this you are better off just using a pot, because for some reason I was thinking you were using 12 volts and not 5.

Sorry, I should have said something earlier.

ElectricSpidey, thanks for checking. I was looking forward to building a circuit with a transistor in it (my first!), but I do want to wind up with a functioning light panel as well. Including the NPN in your schematic drove me to research power transistors, enough so that now I have a better idea how one would be used in a circuit.

 

If using pots only I would stick with post # 25, # 37 not good, 10k way to high.

Bernard, so 10K is way too high; 25 ohm or 100 ohm-or both, as you suggested, would be a better choice? I have all of those pots.

 

As this is mostly a learning experience and most parts are on hand, why not try all 3 suggestions. A pots, post #25, B pots with a transistor, post #24, C PWM.
Slowly increasing V to panel, P, shows no change until V reaches about 2.3 V & then seems to brighten with increasing V. To avoid the dead zone with A or B a second pot can be added to bias control pot to start at about 2.3 V. AS 2,3 V is almost 1/2 of supply, the new pots should be slightly larger than control pot, A then 25 to 100 ohm & B 10k to 100k. After adjusting
second pot for just before first light, it can be measured and replaced with a fixed R, A = around 18 ohms, B = around 9.1k.
B does not seem to reach full bright so simple trial add a 1.5V battery between pot wiper and base, + to base. A step up in brightness? Yes but we want it full bright then go to C, PWM. An old tried and true PWM by Wendy. Replace M with P. CR 1,2, skip 3, 1N4148, Q 2N2222, 5V for 9V .

 

R5 =56- 62 ohm. Q1 darlington or LL N ch FET might be better.

 

So I don't need the transistor at all? Just the pot? So that with the pot at zero, all current is going to the LEDs, thus bright LEDs, and as I turn the pot toward greater resistance, the LEDs dim? But the available current must be more than .6A, or is .6A enough? Would this be the new schematic?
View attachment 220497

I got some results with this circuit (see post #37), but not what I was hoping for-which could be due to my total lack of experience at breadboarding. This is my first effort. I connected the breadboard to a little Elenco kit power supply and connected the positive and negative breadboard rails through the pot to the light panel, and turned on the PS. The good news is that 1. I had the polarity correct and 2. the panel glowed, indicating that the LEDs were all intact. The bad news is that the only adjustment I could achieve with this circuit is via turning the power supply up or down. Varying the pot made little, if any, difference. I also tried jacking the panel into a 6volt wall-wart with a 5.5mm connector. Result: nice, bright panel, but, of course, no variability. So for the next trial, I'll set up a 5-volt wall-wart more realistically with the same components going to the light panel. I'll have to study up on how to translate the schematic connections into a breadboard wiring scheme.

 

I got some results with this circuit (see post #37),

Where you using a 10K pot? If you are going to do this with just a pot then wire the circuit as below.
Otherwise your best bet is to use the circuit ElectricSpidey posted in #24 but use the 6 volt power supply.
SG

 

When the pot is turned to the "bright" position, how quickly will the LEDs burn out?

 

I wouldn't bother implementing a PWM circuit unless correct and consistent LED color were a primary concern or PWM was readily available as the easiest option.

 

When the pot is turned to the "bright" position, how quickly will the LEDs burn out?

They won't, there are series resistors for each LED. Not shown on the TS original drawing. Will edit drawing so there is no more confusion.

 

I got some results with this circuit (see post #37), but not what I was hoping for-which could be due to my total lack of experience at breadboarding. This is my first effort. I connected the breadboard to a little Elenco kit power supply and connected the positive and negative breadboard rails through the pot to the light panel, and turned on the PS. The good news is that 1. I had the polarity correct and 2. the panel glowed, indicating that the LEDs were all intact. The bad news is that the only adjustment I could achieve with this circuit is via turning the power supply up or down. Varying the pot made little, if any, difference. I also tried jacking the panel into a 6volt wall-wart with a 5.5mm connector. Result: nice, bright panel, but, of course, no variability. So for the next trial, I'll set up a 5-volt wall-wart more realistically with the same components going to the light panel. I'll have to study up on how to translate the schematic connections into a breadboard wiring scheme.

Here it is. See attached. The figure at left is one agreed-upon schematic for a brightness control on the light panel. The righthand
figure is my diagram attempting to restate the schematic in a closer approximation of the layout of a breadboard. Do they amount to the same thing?

Where you using a 10K pot? If you are going to do this with just a pot then wire the circuit as below.
Otherwise your best bet is to use the circuit ElectricSpidey posted in #24 but use the 6 volt power supply.
SG
View attachment 221153

Thanks, SG. That circuit looks quite doable, more so than the more elaborate two-pot setup I'm trying right now. I have a 10-ohm pot for it, and I ran it on a 6V wall-wart without any problems-turn it one way, it gets brighter, the other way, it gets dimmer. I'll try your circuit.

Where you using a 10K pot? If you are going to do this with just a pot then wire the circuit as below.
Otherwise your best bet is to use the circuit ElectricSpidey posted in #24 but use the 6 volt power supply.
SG
View attachment 221153

I wouldn't bother implementing a PWM circuit unless correct and consistent LED color were a primary concern or PWM was readily available as the easiest option.

A PWM works fine. I tried it, but I didn't learn anything, so I'm trying to find a solution that forces me to actually build a circuit. The first time I tried the circuit on the left above, the light panel's brightness was affected by varying the incoming voltage at the power supply, but not by turning the 10k pot. That result was confirmed by trying a 5-volt wall-wart in place of the adjustable power supply. the panel came on, but turning the pot didn't affect the brightness.

 

Hello,

The last circuit will not work.
The leds will always have maximum brightness and when the wiper of the potmeter is going to the lower side, the potmeter will burn out, as the full voltage will be on the track.

Bertus

 

R5 =56- 62 ohm. Q1 darlington or LL N ch FET might be better.

Bernard, I've been trying out most of the circuits that have been posted here. Of the lot, setting aside the PWM circuits, yours, using two pots, is the one that worked right on the first try. It's exactly what I was hoping for. I'm setting aside the PWM circuits because yes, they work, as I expected they would, but where's the fun in that? Yours I had to mock up carefully, then plug it in and wait for the smoke. There was no smoke. It worked. I still want to try ElectricSpidey's circuit with a transistor, but I screwed up my first attempt by foolishly omitting the heat sink (yes, they are necessary), so I have to wait for more transistors and heat sinks to arrive. So thanks for the schematic.