Gemma design question 5v

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GhostStrype
 
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Gemma design question 5v

Post by GhostStrype »

So I asked part of this in another thread but wanted to be more specific and make sure before I out fry stuff, but say I have a lot of:
Gemmas,
logic level shifters: 74lvc245s,
sensors,
5v 4a supplies from other projects and more on the way
DC panel jacks
extension cables
access to power for now (will add batteries in next time around especially for trinket with dotstart motion effects with portable power)

Can I just staight plug in (after a big capacitor close to gemma&leds) to the 5v to the gemma with its regulator?
This is from Gemma tutorial:
"You can plug anything from around 4VDC up to 16VDC, but we suggest 4-6V since higher voltages just get wasted as heat. This input is polarity protected. If the green PWR LED lights up, you're good to go. There is no off switch on the Gemma, so unplug or switch off the battery pack when done."

Is it alright to just 5v staight into the gemma from a DC panel jack with big cap across terminals in right polarity, to LED power distro terminal blocks (those snap terminal ones have worked quite easily for prototyping and modular design) straight into the gemma?
If not does it need or should have some protection circuitry? or is it really better that i can get 3.3v linear regulator device?
If that is not great i can get 3.3v regulators. The LEDs will be powered from those 5v 4a supplies. maybe 60 LEDs plus the gemma and one sensor on the circuit. The gemma would be very miniscule if regulator is meant for 800mA I bet no heat sink would be needed (would test anyways to make sure), but does it still need some protection circuitry with all the LED current going around if 50 led's are pure white drawing some 3amps +gemma + linear voltage regulator loss.

I just want to power as many of the gemmas off the same power and not worry about charging a possible 24 gemma party worth of lithium whichever if you get my drift. although I do eventually, and the circuits are all in altoids tins to be modular and portable as a next step. This time around they are part of a large installation that will have lots of sensors changing effects of similar patterns, but vary slightly different based on sensor input. They will be installed vs portable, and I basically want as many of the the suckers alive without battery input and using that 5v supply it will need anyways.

5v trinkets are coming to the party too with this next large order, but I want them to be able to do their own thing and just be the easier ones to setup. I already have the gemmas and all those parts, so ordering like a 3.3v voltage regultor for gemma or not needing one vs having to buy maybe 24 trinkets to replace or 24 batteries that then need to be charged and need to be accessed in the structure.

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adafruit_support_mike
 
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Re: Gemma design question 5v

Post by adafruit_support_mike »

GhostStrype wrote:Is it alright to just 5v staight into the gemma from a DC panel jack with big cap across terminals in right polarity, to LED power distro terminal blocks (those snap terminal ones have worked quite easily for prototyping and modular design) straight into the gemma?
Yep. You don't even need the capacitor unless your power supply is badly regulated.

The Gemma has an onboard 3.3v regulator that will take care of the power.

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GhostStrype
 
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Re: Gemma design question 5v

Post by GhostStrype »

Yep. You don't even need the capacitor unless your power supply is badly regulated.
And just for reference what would be bad enough?

This project has mostly double headroom switching supplies, but if it ran off AA or AAA (easy to source from other people's dead electronics) where voltage sags at end of battery life. Is that a place to actually worry about using a regulator of some sort (i dont think those normal 3.3v to220 package ones will work because they want 5v to provide 3.3v, but whatever regulation needed).

Or is this more to the scale of almost square wave generators like a cheap outdoor power generator where they stray from sine wave power? I have them and put them in anyways most of the time once there is a meter of LEDs or so near digital circuitry, but it would be good to know like how bad each situation is.

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adafruit_support_mike
 
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Re: Gemma design question 5v

Post by adafruit_support_mike »

GhostStrype wrote:And just for reference what would be bad enough?
Operationally, anything so bad the microcontroller can't run properly. Ripple larger than 20%, peaks or dips that last more than a few milliseconds, etc.
GhostStrype wrote:if it ran off AA or AAA (easy to source from other people's dead electronics) where voltage sags at end of battery life. Is that a place to actually worry about using a regulator of some sort
Battery power is smooth enough that you don't have to worry about ripple. A regulator won't hold its nominal output value if the input voltage drops below about half a volt of headroom, but that won't matter unless you need specific voltage accuracy.

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