Power off delay.
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Power off delay.

by JStorto on Tue Nov 20, 2012 4:39 pm

Hello All!
Just a little back round on my project.

I bought six meters of RGB LED strip. My plan was to run it on my truck for: Running lights, Emergency Lights, and just showing off. The Strips are attached to my truck and everything works. It's a very simple set up. I have for Off/On switches that act as a Binary number, each number equals a different pattern. I did this so I can just leave the "Running Lights" switch on and the truck will run the pattern every time it's turned on.

I'm starting work on the power board for my controller. It will have (2) 5v power supplies that will be able to supply 5A of current. It will also have a 12v switched regulator with protection diodes just in case I get spikes etc from the trucks "dirty" power.

I would like the three separate regulators/step down supplies to have a (X) second delay before turning off. This way I could run "off" patterns automatically, but not leave everything on when I turn off the truck.

I have searched the forums but I get 113 pages of "no delay blinky" schematics vice "delay off power" results.

I have attached I simple schematic, I don't know if this is the way to go, or if I should use a monostable 555 timer circuit. I been trying to design one, but I am still quite the amateur. Any help would be greatly appreciated.

PS. I'm extremely happy with my results so far, and would like to thank the adafruit team for all their help and supplies so far.
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Re: Power off delay.

by tastewar on Wed Nov 21, 2012 8:18 am

Sounds like you want your power supply to get its 12V power from a circuit that's always on in your truck. One thing you could do is find a 2nd circuit in the truck that turns off when the ignition is off, use that to energize a relay so that when the relay turns off, it brings a digital input on your microcontroller HIGH or LOW. You can use that transition to initiate your "off" pattern, and start a timer for turning things off.
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Re: Power off delay.

by Zener on Wed Nov 21, 2012 7:33 pm

I don't think the OP has a microcontroller. Let me know if I am wrong about that. If there is a microcontroller then there are lots of ways to do it. The circuit posted looks like it does use a constant 12V and a switched 12V. There are some issues with it. First of all, you have to determine how much current is flowing out the +12Voutput. If you are supplying (2) 5A linear regulators then you need 10A. I am unclear where the third regulator is. If your (2) 5V regulators are switchers then you might get away with 5A. Either way, a 2N2222 is only good for maybe 500 mA. Maybe not even that without a heat sink. So you need a much bigger transistor. And it is unclear what time delay you would get. I thijnk it will be very short. It would probably be better to use a relay which can handle the 10A better, and some RC timer circuit to control that. You could use a comparator that drives the 2N2222 and have that drive the relay. Good luck!
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Re: Power off delay.

by JStorto on Mon Nov 26, 2012 11:16 am

I am using a micro controller, but I Also have two 5v(5A) step down(buck) regulators to turn off as well. If I don't turn them off. which-ever pattern was on the LED strip when the micro controller was on will stay. I have the LPD 8806 Digital Addressable RGB LED strip - 6 meters.

In case I was unclear in the OP. I just want 12v constant available for a couple of secs AFTER 12v switched is removed. But if 12v switched is turned back on before the 12v constant turns off, the circuit stays on.
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Re: Power off delay.

by dyslexic on Mon Nov 26, 2012 4:03 pm

elec. cap will delay a circuit, ham radio uses caps to delay ptt circuit
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Re: Power off delay.

by JStorto on Tue Nov 27, 2012 10:06 pm

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Re: Power off delay.

by GeorgeIoak on Thu Nov 29, 2012 12:02 pm

You might be interested in this power board I designed and just ordered, http://forums.adafruit.com/viewtopic.php?f=47&t=34598. I brought the enable pin of the switcher out to a header so you could use that to delay the power off of the LED strips and MCU.
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Re: Power off delay.

by JStorto on Tue Dec 04, 2012 5:45 pm

Just an update for anyone that is following this thread. I ended up running the 12 switched through a voltage divider and using it as an input to the arduino, then had all the lights turn off when the 12 switched wasn't present. The arduino is always on but with no LEDs on, uses around 250mA. I guess I can live with that.
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