kids oven and stove led circuit

[EricD]

Hi guys,
I'm building a kitchen with a tv furniture and I bought some 12v 8mm red led strip to act as heating elements and get a 12v 1A DC power supply.
I first wanted to put potentiometers on the board to have different lighting intensities but that would light the LED as soon as the switches are turned on.
So, I realized I needed it delayed with a dimming effect reaching the intensity where the potentiometer (counter-clockwise if possible) has been set.
Like the real appliance it need to "warm" and "cool down" slowly (dimmer) but the delay may only be used when the pot is turned ON.
4 different LED circuits on the stove and 1 inside the oven.
A white light will also be put in the oven to see through the door window. Another light inside the refrigerator and above the counter plus (just maybe) a little DC exhaust fan above the stove.
The real stuff transformed for kids, what do you think?
Anyone to help me with this challenge?

[kam]

Here is a good start for you:
http://www.pcbheaven.com/circuitpages/LED_Fade_In_Fade_Out_Dimmer/

What you ask though is kinda complicated and not simple to design if you do not know good electronics. But the above circuit will help you a lot

[EricD]

That's the page who brought me here and I get the stuff today. There is no BC transistor above 200 so for the 548 i will use a BD243 but for the BC257 I don't know what to use.
Sonce each part will drive lot of power i'll have to reproduce this circuit for each component I think.

[kam]

Sonce each part will drive lot of power i'll have to reproduce this circuit for each component I think.

Yes you do! Or you have to use a bigger transistor instead.

[EricD]

I grab tip121 & tip125 transistor but i'll need to make lots of change for the resistors used in that circuit.
The strip specsheet say there 30 led per meter and can be cut every 3 led. There's also a resistor already in place between the 1st and 2nd led of every trio.
It comes in 5m roll with a 12v 1amp dc power supply and the specs says that 2m draw 6watts of power for .5amp if my math are still good. So the 47ohms limit resistor is supposed to fit and the pot will replace the standard switch.
Any tips that can help?

[kam]

If you are talking about a led strip, then you do not need a limiting resistor. Each strip has built in resistors

[EricD]

That what i tough but was sure if their purpose was to limit or to have a more stable voltage between each led.

Have look at other post and saw the LED driving amd control tutorial. My 8 stripes of 3 led were plugged in parallel and it's not recommended from whatni have learned.

Do i have to use a normal led (diode) inside the circuit or is it optional and can i replace the normal switch by a pot and, if yes, will it help to give theneffect that i want? (Fade in to desired lightnings)

[kam]

Since you use a strip and each pair has its own resistor (used also as balancing resistor) then you can safely plug strips in parallel, as many as you wish. Dont worry.

I do not know why you want to use a normal led inside the circuit. i do not see why should you.

As for the pot, most likely you cannot use it. The fade will be bad, and also there will be lot of power dissipation on the pot and may destroy it. Use a linear controller instead:
http://www.pcbheaven.com/circuitpages/Simple_Linear_Fan_Controller/ (replace fan with your leds)
or use a pwm controller
http://www.pcbheaven.com/circuitpages/High_Frequency_PWM_Fan_Controller/

[EricD]

When you open an element of the stove, at max they will be bright orange like fire after a few minutes but if you turn it to med you wont have this result.
Thats why i want to use a pot to turn on the circuit to the desire intensity.
I know that i could just do a on/off led and that would be way simple. But i want to give something more to my daughter, i want to surpass myself so she will have something that reflect how i am and want her to be with her own self. Go over the limit and the confidence to accomplish great things.

[kam]

maybe use the first circuit from this page?
http://www.pcbheaven.com/circuitpages/LED_Fade_In_Fade_Out_Dimmer/

[EricD]

Yes i start with this one but nothing happened with i put on the power.
I tried again after removing the limiting resistor without success. Tonight i will try again with the tip121 transistor. I thing that the other one was the plugged correctly and that it may be dead.

If it work i will check the dim and delay abd see if the second one will be better.

[kam]

Sure you need to remove R3 from the circuit ( talk about the first circuit with R3 connected at the emitter of the transistor).

[EricD]

It doesn't work and i can't figure out why.

[EricD]

Nevermind!
My R2 was smaller than R1 so that's the reason it wasn't working.
Someone must have misplace it at the store and i assume without checking the color code.

[EricD]

?aaaa, Everything looked cool but i wasn't satisfied because I had no brightness controler.
The delay is long, the fade is smooth but it's only on and off.
I'm trying to make a 5v-12v circuit to regulate with a pot the max brightness led will have.

I've looked at the circuit but i dont undrstand everything. It use the 3 pins of the pot in the middle of 2 resistors in series.
If -0 is at the left where do I place de +12v in and the variable voltage out that goes to the adjustment pin of the transistor.
Why doin it that way when usually only 2 pins are placed on the pot with no +12v connected to it and only one resistor placed on the adjustment et Vout of the transistor?