Gradual Ramp-Up/Down DC Voltage

I have a timer module that has an option to ramp the DC input power up/down gradually over a period of 4 seconds. So when it applies power through its relay, it can do so by going from 0v to full voltage (in this case 12v) over 4 seconds, and then when it powers down its relay, the voltage drops from max to 0v gradually over 4 seconds. This is an optional feature that I can enable, and it would be beneficial for some of the projects I'm working on. But I'm wondering if this would have any adverse effects on the Arduino board. Could it potentially corrupt the contents of the flash memory?

Relays are mechanical switches operated by an electromagnet. They can't "ramp down".

MarkT:
Relays are mechanical switches operated by an electromagnet. They can't "ramp down".

I guess I forgot to include the words "pulse width modulation" in my original post. I don't think it actually changes the point of my question. It's not like I'm making up documented features of my timer...

You definitely don't want PWM on a microcontroller power rail.

Why not? Is the Uno's onboard voltage regulator unable to cope with the super short period of time when the voltage drops below 5v for about 1 second during startup and shutdown?

Voltage regulators regulate DOWN, not up! They have to have a supply of more than 1 volt above their putput.

Paul

Well yeah, I know... not sure why you're telling me that. I never made any claims otherwise. I'm feeding the board 12v, as I stated above. All I'm asking is:

Will powering up/shutting down an Uno using a gradual voltage cause any potential issues with the flash storage or the voltage regulator that's built into the Arduino board?

I'm not sure how this got so far off course...

Bad idea to PWM or slowly ramp up/down the power supply of an Arduino. Why are you even asking that.
Don't see how anything can be damaged or deleted, but the MCU could go through several interrupted setup cycles. Who knows if the sketch will do what you have told it to do.
Don't know which Arduino, but 12volt is borderline too high and some (Nano) will be damaged.
Can't power anything from the pins at that supply voltage either.
Leo..

Wawa:
Bad idea to PWM or slowly ramp up/down the power supply of an Arduino. Why are you even asking that.
Don't see how anything can be damaged or deleted, but the MCU could go through several interrupted setup cycles. Who knows if the sketch will do what you have told it to do.
Don't know which Arduino, but 12volt is borderline too high and some (Nano) will be damaged.
Can't power anything from the pins at that supply voltage either.
Leo..

I'm confused. The specs for the board I have state that input power through the DC jack can be anywhere from 6v to 20v, with 7v to 12v recommended. I'm right in the recommended range, and nowhere near the limit. My project has a bunch of components that require 12v power, and I'm hoping to be able to power them all from one source coming from the timer module. Using the ramped power option makes the final product more elegant.

So far in my testing, everything seems to work fine, but this is just short-term bench-testing.

I guess I don't get how the on-board voltage regulator works. I assumed it was a buck regulator that provides no power until input is 6v, at which point it feeds 5v to the board power rail. Is that not correct?

Also, why wouldn't I be able to power anything from the pins at that supply voltage? The Adafruit music shield recommends power through the DC jack otherwise the shield doesn't get enough current to fully power the 2x3w speaker amps.

You can't draw more than 100mA from an Uno when powered from 12volt.
If you do, the linear (not buck) 5volt regulator overheats and shuts down (if you're lucky).
The advertisers have conveniently forgotton to put that in the specs.

The exception is the V-in pin.
That pin is directly connected to the DC socket, with only a reverse protection diode in between.
You can draw (almost) 1Amp from that pin, because it basically has nothing to do with the Arduino circuits.
That Adafruit shield is most likely drawing it's power from that pin.

If you don't connect other power-hungry devices to the 5volt/MCU pins, then 12volt on the DC socket is ok.
Leo..

Wawa:
You can't draw more than 100mA from an Uno when powered from 12volt.
If you do, the linear (not buck) 5volt regulator overheats and shuts down (if you're lucky).
The advertisers have gonveniently forgotton to put that in the specs.

I didn't realize it was a linear converter. Does that mean I'd be better off putting a buck regulator between the power supply and Arduino and supplying 7v instead of 12? Seems like dissipating 6v of heat is a giant waste of power, especially since my project is battery-powered.

Don't know. You have to add up power consumptions.
The Uno (50mA) might be a fraction of the draw of that shield.
You might only save 20mA there.
Both don't seem very good candidates for battery power.
Leo..

If I understand the question, you want to know if ramping up the input voltage to an UNO will harm it.

I would be concerned the POR would not work correctly as it is a simple RC and the slow rise time may not result in a sufficient delay to positively reset the processor.

JohnRob:
If I understand the question, you want to know if ramping up the input voltage to an UNO will harm it.

I would be concerned the POR would not work correctly as it is a simple RC and the slow rise time may not result in a sufficient delay to positively reset the processor.

Thank you, that's exactly what I needed to know.