Gradually increasing 12 VDC LED lighting circuit.

[Matrooo69]

I need help on a DIY LED lighting project for a remote location. I am trying to set up a motion activated 12VDC lighting circuit that will gradually light up an LED over a 180 second period. It will be set up in remote locations and use a 12 volt battery and a solar charger. There are plenty of motion activated, battery powered LED lighting systems on the market but none that I could find that will gradually increase the lighting over several minutes. Is there an "off the shelf" devise that I can purchase and add to an existing LED circuit that will gradually increase the current to the LED or will I have to build something from scratch?

Any help or advise would be appreciated.

 

[Audioguru]

I think your vision's response to brightness is logarithmic (twice the amount of light appears only a little brighter) so a linear 3 minute ramp will probably be wrong for your application.
But your 3 minute ramp is such a long time that you probably cannot remember the brightness 20 or 30 seconds ago or a minute or two ago, so maybe a linear ramp will be fine.
I doubt that anybody makes such a thing so design and build it from scratch.

 

[Matrooo69]

This setup is being built to monitor wild animals at remote locations so the gradual ramp up of light over 3 minutes is needed to keep from spooking the animals. The sudden switching on of light drives the animals away.

 

[BradtheRad]

Here is a concept which might work.

You can vary the duty cycle from a 555 timer IC, by changing the voltage at its 'CTL' pin. Start a capacitor charging (C2 in the simulation below), feed its voltage to an op amp, and apply it to increase the duty cycle.



The scope trace covers a period of 34 seconds. The pulse rate is slowed down to make individual waveforms obvious.

In a real circuit, reduce C1 so pulse rate is faster.

Also reduce C3. Its purpose is to smooth the pulses through the led. Or else you might prefer to put a choke inline.