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0v -> 12v voltage increase over 10 minutes? (Sunrise alarm clock circuit)

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resident gearhead

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Noob here. I have some electronics experience but not much.

I'm looking to go from 2-3 volts to 12 volts over roughly 10-15 minutes. 4-6 amps at full power.
This is to power a strip of SMD LED lights for a 'sunrise wake up timer' to help me wake up more effectively in the winter months.

This is what I've found so far on instructables. This was designed for 5V but I believe it'll handle the power I'm looking at (12v @6a). Can I just wire up my 12v power and LED strip to this circuit as is, or should I adjust any of the components?
Also, what about adjusting the speed of the circuit? I assume I'd swap in a potentiometer in place of the 1M ohm resistor, but not sure of what components to use (most pots I see are only 10k ohm).

https://www.instructables.com/id/Sunrise-Alarm-Clock-1/step2/The-Circuit/

dimmer.jpg

Thanks in advance for your help!
 

SunnySkyguy

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This 60W to 72W watt load at half power will also dissipate 50% of the power in the MOSFET. Not good.

A slow rising PWM from 0 to 100% with 8 bit resolution might be better. with 12 V LEDs driven with a 30A Mosfet for low drop voltage from logic gate levels.

This might be done with 3 clocks.
1) a step clock 0.284Hz for 15 minutes
2) a PWM clock ~200Hz
3 ) a Master clock = 51kHz = PWM clock * 256 to obtain 256 steps in duty cycle from 0 to 100%.


With 256 levels in 15 minutes or 900 seconds , this is ~ 3.5 sec. increment
1/256 step or ~0.4% power step every 3.5s is 0.284Hz for the increment clock.

PWM rates above 200 Hz or more should be low flicker .
A master clock needs to be 256 * this or 51 KHz, (which may be higher than some LED's can be modulated.)

It may be feasible to attempt this with a counter generated phase pulse- controlled triac using AC line powered LED, with slight flicker at 120Hz thus eliminating the PSU and LED design.
 

asdf44

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Noob here. I have some electronics experience but not much.

I'm looking to go from 2-3 volts to 12 volts over roughly 10-15 minutes. 4-6 amps at full power.
This is to power a strip of SMD LED lights for a 'sunrise wake up timer' to help me wake up more effectively in the winter months.

This is what I've found so far on instructables. This was designed for 5V but I believe it'll handle the power I'm looking at (12v @6a). Can I just wire up my 12v power and LED strip to this circuit as is, or should I adjust any of the components?
Also, what about adjusting the speed of the circuit? I assume I'd swap in a potentiometer in place of the 1M ohm resistor, but not sure of what components to use (most pots I see are only 10k ohm).

https://www.instructables.com/id/Sunrise-Alarm-Clock-1/step2/The-Circuit/

View attachment 120892

Thanks in advance for your help!

Well that's an unnecessarily bad circuit for controlling current but regardless, SunnySkyguy pointed out the primary problem with any linear solution: power dissipation. Linear current circuits work by essentially burning up the excess power. In your case with a 70W load that mosfet will overheat rapidly (anything >~1W needs special consideration for normal large packages like TO-220)

PWMing is a better all around solution.
 

resident gearhead

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This is a manual pwm dimmer I have that works well with these LED strips. Is there a way to replace the (I believe 1K ohm) pot with a capacitor/resistor combo (or other circuit) to get the automated dimming?

IMG_9635.JPG

IMG_9636.JPG

IMG_9637.JPG
 

SunnySkyguy

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If you have a hard time waking up, consult with a Doctor

You mean you would like to add a 10 minute ramp generator to a D/A converter resistive ladder to emulate a pot? That's possible but it wont fit wont on the board.

555 timers more than 5 minutes are unreliable but if you tried it would be the CMOS version with a polyester film Cap and very clean supply.

https://www.555-timer-circuits.com/common-mistakes.html
 

schmitt trigger

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Waking up with a slowly increasing light level is a wonderful way to wake up!
It is not as irritating as an alarm clock.

The best approach is the slowly ramping up PWM levels, as Sunnyskyguy mentions.
 

SunnySkyguy

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Re: 0v -> 12v voltage increase over 10 minutes? (Sunrise alarm clock circuit)

I designed something similar, except it was a sunset LED celing light with an adjustable SMPS ( modified Universal Laptop charger with 4 pins and remote sensing.

With about 50 Watts of LEDs as the voltage rose from 12 to 20V, it started to brightness RED then RED& Yellow , then R & Y & White, based on the string voltage for each colour I selected.

I discovered that there was 2.5V Vref on the 5 pin connector to coaxial DC plug and that could be used to scale the output back to Vin to adjust Vout from 10 to over 40V with 65W.

The White was brighter than direct sunlight. ( She wanted it that way) with all light beyond 30 deg from vertical blocked for no glare. ( I wanted it that way )

9304833418E122A.jpg


Here's a still image.

- - - Updated - - -

Just a simple conceptual example of a digital counter, derived from RC relaxation clock in the CD4060 then use suitable PWM frequency and binary outputs to binary R weighted values as a D/A converter. The triangle wave could be LPF from a square wave and the last binary count stage to stop the clock.

CD4060 is simple and most of you know how this works.
cd4060.gif


WIth a few more connections, one can get the PWM clock, the sunrise step clock and 15 minute timer all in 1 chip.

Here the FET switch is selected to drive whatever current you need and whatever voltage supply.

THis is just a concept of the 15 minute staircase brightness.

slope LED.jpg
 

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