How to: LED strip 12V ON = fade in, OFF = fade out

[May Day]

How to: LED strip 12V - ON = fade in, OFF = fade out

Hi everybody,

I'd like to make my LED strips to turn on slowly and then turn off slowly.

Say I have a 5m 3528 LED strip and when I switch it on, the strip fades in and when I turn them off, the LED strip fades out.

I know there are plenty of ideas online, but they are not what I'm looking for.

This is a good example what I want when he turns his lights on, they fade in, but when he turns them off, they DON'T fade out, they turn off instantly. The link to that project is here: https://www.instructables.com/id/How-to-fit-LED-kitchen-lights-with-fade-effect/#intro Perhaps I can modify it a bit so the LEDs fade out.

I'd appreciate you advices!
Thanks.

 

[barry]

Re: How to: LED strip 12V - ON = fade in, OFF = fade out

I know there are plenty of ideas online, but they are not what I'm looking for.

What AREN'T they what you looking for? You could use a PWM method to ramp up/down your average current.

 

[oufuqiang]

try this......

 

[chuckey]

That circuit will only do one LED @20 mA, if the current is higher use a Darlington power transistor, also I think it needs a current limiting resistor somewhere.
Frank

 

[May Day]

Say I have a 5m strip of SMD 3528, that is 300 LEDs.

This project is for a bedroom so I want the strip to turn on slowly and turn off slowly. Say 3-5 seconds.

 

[barry]

Say I have a 5m strip of SMD 3528, that is 300 LEDs.

This project is for a bedroom so I want the strip to turn on slowly and turn off slowly. Say 3-5 seconds.

I assume that's 300 LEDs in parallel? At 20ma, that's 6 Amps. You'll need a hefty transistor/mosfet.

You can either use the method in post #3, or PWM. The PWM method is more efficient, but also requires more circuitry.

 

[May Day]

try this......
View attachment 95250

Would you please put more light on this? What do these compnents do so I know how to amend your diagram to get it working with 300 LEDs and like barry says 6 Amps?

I assume that's 300 LEDs in parallel? At 20ma, that's 6 Amps. You'll need a hefty transistor/mosfet.

You can either use the method in post #3, or PWM. The PWM method is more efficient, but also requires more circuitry.

I think I rather start with the easier(?) method and then PWM. Why is PWM more efficient? If you have any ideas of how I can easily do it (programming some IC shouldn't be a problem), don't hesitate and please do share with me

 

[BradtheRad]

Here is a variation on the method in post #3. It illustrates how several strings of led's might be hooked up, thus reducing the number of transistors needed.



The potentiometers adjust both the brightness and the on-off times.

The diodes prevent the capacitor from discharging all the way to zero. That way the system does not delay for an extra second or two waiting for the capacitor to reach a sufficiently high level to turn on the transistor.

 

[May Day]

Here is a variation on the method in post #3. It illustrates how several strings of led's might be hooked up, thus reducing the number of transistors needed.



The potentiometers adjust both the brightness and the on-off times.

The diodes prevent the capacitor from discharging all the way to zero. That way the system does not delay for an extra second or two waiting for the capacitor to reach a sufficiently high level to turn on the transistor.

Ok, how can I connect this kind of strip/s to your diagram?

My LED strip is the white one on the left.

I really appreciate your time guys

 

[kam1787]

LED strips are often for a set voltage[ ie 12VDC or 24VDC] and usually have a current limiter built-in

 

[kam1787]

Ok, how can I connect this kind of strip/s to your diagram?

Your positive [red] goes to the V+ and the negative wire goes to the collector of the transistor

 

[BradtheRad]

Ok, how can I connect this kind of strip/s to your diagram?

My schematic is a simplification. It illustrates how a capacitor can soften the on-off transitions which are applied to one transistor. Then that one transistor controls several transistors, each of which turns its load on and off gradually.

Each load can really consist of several led strips, in parallel.

How many strips should you attach to one transistor? That will depend on how much current a transistor can conduct safely.

You must measure the current drawn by an led strip, at its rated supply voltage. It is up to you to experiment with different quantities of strips, and to make sure the transistor does not overheat as it dissipates power.

When you have gotten one transistor to safely power a given number of led strips, then you have the pattern for assembling the remaining strips.

 

[May Day]

My schematic is a simplification. It illustrates how a capacitor can soften the on-off transitions which are applied to one transistor. Then that one transistor controls several transistors, each of which turns its load on and off gradually.

Each load can really consist of several led strips, in parallel.

How many strips should you attach to one transistor? That will depend on how much current a transistor can conduct safely.

You must measure the current drawn by an led strip, at its rated supply voltage. It is up to you to experiment with different quantities of strips, and to make sure the transistor does not overheat as it dissipates power.

When you have gotten one transistor to safely power a given number of led strips, then you have the pattern for assembling the remaining strips.

Thanks for your description

I just found my old Olimex PIC-4550-USB and I was just thinking if I can use it for my project? I can't remember what I used to program as it's been a while :/

 

[kam1787]

yes you can, but it's a bit like using a F1 racing car to go to church on a Sunday.