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General Category => Your projects => Topic started by: EricD on August 03, 2015, 09:32:55 AM

Title: kids oven and stove led circuit
Post by: EricD on August 03, 2015, 09:32:55 AM
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?
Title: Re: kids oven and stove led circuit
Post by: kam on August 03, 2015, 19:04:09 PM
Here is a good start for you:
http://www.pcbheaven.com/circuitpages/LED_Fade_In_Fade_Out_Dimmer/ (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
Title: Re: kids oven and stove led circuit
Post by: EricD on August 04, 2015, 02:38:10 AM
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.

Title: Re: kids oven and stove led circuit
Post by: kam on August 04, 2015, 20:04:36 PM
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.
Title: Re: kids oven and stove led circuit
Post by: EricD on August 07, 2015, 09:51:18 AM
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?
Title: Re: kids oven and stove led circuit
Post by: kam on August 10, 2015, 20:50:03 PM
If you are talking about a led strip, then you do not need a limiting resistor. Each strip has built in resistors
Title: Re: kids oven and stove led circuit
Post by: EricD on August 12, 2015, 07:35:21 AM
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)
Title: Re: kids oven and stove led circuit
Post by: kam on August 20, 2015, 00:15:46 AM
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/
Title: Re: kids oven and stove led circuit
Post by: EricD on August 21, 2015, 08:08:13 AM
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.
Title: Re: kids oven and stove led circuit
Post by: kam on August 21, 2015, 18:41:31 PM
maybe use the first circuit from this page?
http://www.pcbheaven.com/circuitpages/LED_Fade_In_Fade_Out_Dimmer/
Title: Re: kids oven and stove led circuit
Post by: EricD on August 22, 2015, 01:12:56 AM
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.
Title: Re: kids oven and stove led circuit
Post by: kam on August 22, 2015, 22:55:11 PM
Sure you need to remove R3 from the circuit ( talk about the first circuit with R3 connected at the emitter of the transistor).
Title: Re: kids oven and stove led circuit
Post by: EricD on August 23, 2015, 21:36:33 PM
It doesn't work and i can't figure out why.
Title: Re: kids oven and stove led circuit
Post by: EricD on August 23, 2015, 22:05:20 PM
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.
Title: Re: kids oven and stove led circuit
Post by: EricD on September 06, 2015, 09:03:18 AM
?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?
Title: Re: kids oven and stove led circuit
Post by: kam on September 06, 2015, 16:31:42 PM
which circuit are you talking about?
Title: Re: kids oven and stove led circuit
Post by: EricD on September 08, 2015, 04:05:08 AM
http://www.pcbheaven.com/circuitpages/Simple_Linear_Fan_Controller/

It's in fact a 8-12v and not 5-12v so i'll need to decrease R3 for sur but what about the rest? (As asked in my previous post)
Title: Re: kids oven and stove led circuit
Post by: kam on September 08, 2015, 16:35:07 PM
using the pot like i do with the 3 pins, it is an effective voltage divider. R2 is used to prevent overcurrent through the transistor when the pot is set to max voltage. R3 is used to unbalance the pot-voltage divider and thus set a minimum voltage other than 0 volts.
Title: Re: kids oven and stove led circuit
Post by: EricD on September 09, 2015, 06:20:23 AM
My DC power supply is 12.2V. I'm using a 4.7Kohm pot with a switch that I want to enable so the circuit is off. I guess that my + wire will enter one side and a jumper wil go from the exit to the right pin.

The pot have in fact 4.3Kohm when test with my multimeter. R1 is 222ohm for 11.70V max output and R3 is 916ohm for 6.4V min output. I started decreasing R3 from 3.3Kohm giving 8.7V and tried different resistors.

My transistor is an LM317T so at first I tough that it was the reason why I was having an higher minimim voltage output but a 1.5Kohm resistor still gave me 6.85V. I tried with a 560ohm but the output rise so i'm scratching my head right now.

Each circuit of the stove will power 24 smd led (3528) for 167mA of current. Each series ofn3 led have a 330ohm built in smd resistor.
Title: Re: kids oven and stove led circuit
Post by: kam on September 09, 2015, 17:15:20 PM
Oh! The LM317 is not a transistors, it is a linear regulator...

http://www.st.com/web/en/resource/technical/document/datasheet/CD00000455.pdf (http://www.st.com/web/en/resource/technical/document/datasheet/CD00000455.pdf)
Title: Re: kids oven and stove led circuit
Post by: EricD on September 09, 2015, 17:31:36 PM
That's probably why my output is very stable  . Im using 2x .1uf ceramic capacitors btw. It have his own resistance but i can't remember the number i had yesterday. I'll check tonight.
Title: Re: kids oven and stove led circuit
Post by: EricD on September 10, 2015, 04:46:32 AM
Ok I think that i have everything in place to do something great buddy!

I switch the LM317T for one of my TIP121 and manage to drop the voltage to 4.8V. I jump the output of the emitter to the fade in/fade out simple circuit as my voltage input.

Doing this I've notice that under 6.8V it doesn't look good so I put my LM317T back in place with a 1.5kohm since it was giving me the perfect match.

I'll send some pics and/or a link to a video to show you the result.
Title: Re: kids oven and stove led circuit
Post by: kam on September 10, 2015, 20:26:40 PM
a video would be great!  8) 8)
Title: Re: kids oven and stove led circuit
Post by: EricD on September 11, 2015, 05:31:51 AM
With the LM317T the voltage go directly to the other circuit (fade n delay) or maybe i did something wrong when wiring.
So I placed 2 tip121, one for each circuit but I lose 2V at the max output. Another thing is the instead of being lit just a bit at 6.8V (my min output) it drop somewhere aroud 5V.

I'm wondering why they turn on at a different voltage now and what would happen if I place the LM317T on the fade circuit, will it work better?

It's not perfect and I know I can improve it but i'll solder some parts so they hold together in i'll film the rough results i'm getting at the moment.
Title: Re: kids oven and stove led circuit
Post by: kam on September 15, 2015, 08:10:32 AM
The voltage loss is normal with this circuit and cannot be avoided. You should consider a 1.4V drop so if you want max 13v output use 13.4v supply voltage.

You cannot replace the transistor with the lm. But you cannot use the lm differently.Google "lm317 variable voltage regulator". Stop you will get a voltage drop due to the forward diode bias inside the transistor. The lm requires 3 volts to regulate.
Title: Re: kids oven and stove led circuit
Post by: EricD on September 16, 2015, 02:24:15 AM
Yeah I should use a LM2941 which is a low drop out. There's is a way to use the 317 without the 1.5volts drop but it would not stabilize the voltage. (3v drop is for 40v in)
I've been able to do it by changing the pot to a 1k and use a 160 ohm near the LM and a 540 ohm near the ground.
when I add the led the minimum voltage rise higher, it reach around 7.5. I change the setting to "do as if" I want a 3.5v minimum so it was 5.5v with the led.
My max was at 11.something but with the led they don't have the reach 12v to glow at full intensity.

Since the led intensity is decided by the current running through them would it be better if I use the LM317T as a current regulator match with a 7.5 ohms (165mA) and a 470ohms pot (or less)? If so, can it still fits with your fade circuit?

I also bought pwm555 in case. I'm new to electronic* so I don't know what would be the best option for the greatest result.

*If you don't consider the strobe and lights modulator I make in a high school class when I was 16. (Secondaire 4 here in Quebec)
Title: Re: kids oven and stove led circuit
Post by: kam on September 16, 2015, 08:42:09 AM
Pwm solution has almost 0 voltage drop, so you feed 12 you get 12. You can use my high speed 555 pwm driver in my circuit pages and win the match.

As for the current regulator... The strips are designed to operate at 12v without current regulation. Nevertheless you can make a current source to get linear light intensity regulation (current to lumens led characteristic is a straight line) but why bother? You can use the midget linear regulator for your tests. You can find the circuit in my theory pages about linear led drivers

Pwm is the ticket though.
Title: Re: kids oven and stove led circuit
Post by: EricD on September 16, 2015, 23:52:04 PM
Ok i can go with pwm555 but how will i have a delay and fade in/out plus a brightness regulator.

Ive read about the astable mode and my Electrodroid app is very helpful in many circumstances.

I'll check the stuff in your pages but I dont know how everything will fit together inside one single circuit.
Title: Re: kids oven and stove led circuit
Post by: EricD on September 17, 2015, 06:59:39 AM
Well it does work with an ajustable current regulator and almost perfectly to tell the truth. I even add it after your 1st fade in/out circuit.
The emiter of the TIP121 goes to the Vin of my LM317T and at the Vout there's a fix 16 ohms in serie with a 470ohms pot. The left and center pins are join together and the right pin have a wire to feed the leds and another one attached to the LM adjustment pin. The switch on the pot is used to break the +12V that runs from the supply to feed the base and gate of your circuit.

The downside is that when turned on or off I have a delay and the max brightness is also lower due to the currect that is cut-off by the TIP121 (I think).
I've also notice that when I change the intensity slowly the leds just follow the pot. When tried faster a fade is noticeable but too fast will created sudden drop in brightness before it catch back.

I want to give a try with the 555 but as said in a previous post I wondering how to do both things at the same time. Something was telling me that grabbing 556 would be a good idea. ;)
Title: Re: kids oven and stove led circuit
Post by: EricD on September 19, 2015, 05:27:24 AM

The downside is that when turned on or off I have a delay and the max brightness is also lower due to the currect that is cut-off by the TIP121 (I think).
I've also notice that when I change the intensity slowly the leds just follow the pot. When tried faster a fade is noticeable but too fast will created sudden drop in brightness before it catch back.


In fact the downside is not the delay cause it's what I was looking for.
The lower brightness at max can be easily fix by replacing the fixed resistor for a lower value and regain what is lost by th e circuit's components.

The real problem is:

■ When to brightness value change quickly the leds have a "drop".
● By reading your article I came across something about fixing the voltage to have a more stable circuit. Since I'm using a linear regulator I want to know if this apply to me. ?Will it stop dropping if I fix the voltage of LM317?
?Will I have to recalculate the resistors for the adjustable current regulator?
?Will the leds still reach full brightness?

■ If the pot position is change the lights instantly changes.
● Is it possible the have them fade from A to B slower than to movement on the pot?
● If yes, what are my options?
? Bigger capacitance or the parrallel resistor higher value.
? Having the capacitor discharge after a delay and fade is complete.
? Adding new stuff to improve the circuit.

Thanks! :)
Title: Re: kids oven and stove led circuit
Post by: kam on September 19, 2015, 15:45:00 PM
Your regulator is fine to have a stable voltage. you do not need to add anything else. If you want full brightness, you really need higher voltage supply. this is due to the voltage drop on the transistors.
You can try higher capacitors but already you've changed the circuit a lot and i cannot follow unless i calculate the circuit all over again. And unfortunately time is a luxury that i do not have right now.

So, you want something that you turn the pot to a value, and the leds simply follow with a fade in/out delay. You can try this for a change. Use the 317 to make a voltage regulator 5 to 14 volts. Do the calculations to find the proper resistors needed to achieve these values. Remember that you need a higher input voltage, at least 17 volts. You can go with a typical 24V power supply as well.
Then what you wanna have is a voltage hysteresis circuit. You can use this circuit LED Fade-In Fade-Out Dimmer (http://www.pcbheaven.com/circuitpages/LED_Fade_In_Fade_Out_Dimmer/) (i'm talking about the first one). Remove the switch S1 and then connect the output of the lm317 directly to the R1 of the fader. Like before, you need to remove R3 since your leds already have a limiting resistor. The 12V input indicated in the circuit are taken of course out of the LM317 circuit that you made.

Is this what you've already done so far? If not, give it a go. This should work.

Title: Re: kids oven and stove led circuit
Post by: EricD on September 20, 2015, 04:43:18 AM
Right now my dimmer on the lm317 is an adjustable current regulator and is AFTER your fade delayed circuit. I'll switch their order to put them like you said.

I tried it before but when I powered the circuit it was charging to full capacity without being influence by the pot. This was because the base of tip121 was the Vout of LM317 but the collector was on the main 12v of the power supply. Reading your post make me realize my mistake.

My first try was your first circuit and the only change I made was swapping the 470uf for a 1000uf and have more delay. Then I've put another 1000uf in parrallel so time was extended.

T= R.C = 33K.2mf= 66s (to full charge?)
Imax (t=0) = 363.6 uA
Qmax (t-->♋) = 24 mC
*Can't find infinite symbol

Looking at Imax how have it lit in the first place???



Title: Re: kids oven and stove led circuit
Post by: kam on September 20, 2015, 16:52:37 PM
there is a transistor there amplifying the current but 100s of times...

Try the setup that i described. The lm317 has to be connected as adjustable voltage supply, not current!!!
Title: Re: kids oven and stove led circuit
Post by: EricD on September 21, 2015, 07:49:10 AM
With the LM317T the voltage go directly to the other circuit (fade n delay) or maybe i did something wrong when wiring.

The Vout of my voltage regulator was going in the base of the tip121 that I'm using in your fade in/out but the collector was plugged to the  power supply 12V and not to  the output of my voltage regulator like the base was.

I've kept the circuit and worked at the other end of my breadboard so it will be fast to test it again but not tonight...it's almost 1:00 AM here in Montreal and I'm working. I go to sleep almost at 2 o'clock every night since I start this project. Would be ok if I didn't had to wake at 6.

*I don't have something higher than a pc power supply regarding DC V.
Title: Re: kids oven and stove led circuit
Post by: EricD on September 21, 2015, 09:12:01 AM
Just found this link on another website but just miss it while surfing yours

http://pcbheaven.com/circuitpages/LED_PWM_Dimmer/

Got everything in my stuff so if pwm is the ticket, I think we might have a winner...
Title: Re: kids oven and stove led circuit
Post by: EricD on September 23, 2015, 08:28:05 AM
Ok I tried it the way you told me and it works. I did put the power supply 12v inside the collector instead of feeding it with my regulator's Vout.

I placed 2 1000uf capacitors in parrallel to see the delay.

-When moved only a little nothing happen, just more brightness.

-When moved fast there's something like 2 sec of delay before the fade is applied.

-When power on the minimum brightness takes lot of time to happen but your 2nd fade circuit show how to have a minimum charge in the capacitors.

-When set to max it's still not fully bright but you told me that I need more power. I prefer heading for an LDO solution with less than 0.5v dropout.

-When set to max the leds are flickering amd this may be just becaused nothing is solder. Unless noise could happen but I've read just an intro on this subject.

I'll put a video tomorrow so you can see.
Title: Re: kids oven and stove led circuit
Post by: EricD on September 25, 2015, 07:16:31 AM
Disappointing...

It just won't work that way. So much te spent but at least I'm keeping the knowledge I gathered.

It seems to be phase-shift dimmer that I'm looking for if I go all the way with leds. When pot moved from point A to B the change of brightness is not instant but starts slowly fade to reach the new set value over a certain time.
Hysteresis, from what I've read, will kicks in when the voltage overpass a certain point (1/3 - 2/3 of voltage).

Doin this project with leds makes it harder. Bulb light are resistive so dimmer are more user friendly and leds will dim by regulating the amount of current. But even with a good adjustable regulator, some leds in the string will be brighter plus capacitors charging/discharging will be really tricky (sometimes to quick other times to long).

Do you know how to achive pwm dimmer with phase shift? If this way is not possible then only programation of software in a chip woll work.

P.s: video only show jothing (everything*) but succes plus dark to see and me trying to speak english in a shy way.


Title: Re: kids oven and stove led circuit
Post by: EricD on September 27, 2015, 16:23:07 PM
I tried to upload a video file from my cellphone but it didn't worked so I'll try from a pc later today.

I've removed the LM317 and plugged the VR wipper directly to the 4.7 KOhms of you fade in/out simple circuit givin me back +2v. It was way much better. I still need to swap the 2 resistors to improve voltage adjustment but the range was already wider and the leds more brighter.

I'm considering using your 2nd fade circuit since it have more flexibility to have longer response time.

I didn't think it would be such hard work when I step into the project. Knowing not enough I had to go through loads of information and this made a long road to succeed.

As a representative my machines problems troubleshooting were improved and my boss even suggest paying for an electronic class and take me as a repair technician.

Thanks for your patience and i'll share the final results with you I promise!
Title: Re: kids oven and stove led circuit
Post by: sanjaybaghela on September 30, 2016, 08:47:34 AM
nice project
sophie smith