power stability for uSD card writing

[linuxgeek]

I've been looking through posts and see others have tried stabilizing power for other high current draw components.
I've seen this component tried: http://www.mouser.com/search/ProductDetail.aspx?R=0virtualkey0virtualkeyMCP1702-3302E-TO

from this discussion: https://forum.pjrc.com/threads/24343-Teensy-3-0-3-3V-pins-maximal-Current

I'm trying to avoid having the uSD card writing draw too much current and impacting a microphone.

It looks like I can wire this to the 5V input and then connect the output to the uSD card adapter.
Likely I won't be running off USB, but instead 3.7V-4.2V battery. This looks like it should still work.

Should I consider using this unit to power the teensy too? Connecting the output of this to the 3.3V input on the teensy & to the uSD adapter?
Would this component be better at regulating power on the teensy than the on-board voltage regulator?

Thanks.

 

[GremlinWrangler]

That will work, though if you are designing for low noise putting the micro on the regulator and using the Aref pin may get you better results since you also get rid of the Teensy induced noise then as well. Depends on your SD card not browning out the Teensy while writing, which depends on how much else you have drawing power.

 

[linuxgeek]

Is the 3.3V input on the teensy considered Aref?
I'll try it a couple different ways and see, but I just wanted to make sure I was understanding correctly.

Power draw will be just sdcard writing and the mic. If I use the audio board I think it adds some power draw, but if I use a mic with ADC, I think it's less.

 

[GremlinWrangler]

You can probably use everything of the one supply if you have decent caps (low ESR, not just biggest in the parts box) on the SD card, but if you do want to get minimal noise on ADC you do is a dedicated supply for it and then have aref connected and set for external reference. Then the ADC compares the analog signal to the aref, not the possibly noisy 3.3V used by the default ref (there is also a 1.2V internal ref useful in some cases). Suspect the audio part of this will be adding more noise than this gains you, but it's the direction to go for best practice design.

 

[linuxgeek]

Thanks, good to know about the low ESR, makes sense as I read about that now. I'm glad I know now so that I don't have to pay shipping again to get this later.

I see that the ARef pin is on the underside of the teensy, and now this all makes sense to me. Thank you.

I have good examples of the 172Hz (and harmonics) artifact from the uSD writing, so I'll post back with the resulting spectrum of the audio with each power scenario.

edit: OK, one more question if I could. What would be considered a low ESR? I see a lot of mOhm ratings, but I think it should be less than 1 ohm? Any useful convention would be helpful. I was reading that any ceramic is usually good.

 

[linuxgeek]

I ordered some parts, but in the meanwhile I did a little testing. I soldered everything and shortened the wires.

With the audio board and the provided electret mic from pjrc, I get some 172 artifact with the harmonics. This one uses this mic: https://www.digikey.com/product-detail/en/pui-audio-inc/AOM-6738P-R/668-1296-ND/3189921


With the audio board connected but using the ADC with the electret mic provided with the ADC mic board (need to find out what mic is used), I get a peak at 115Hz, but no harmonics. This seems unrelated to the sd card writing, and may be actually present or some other power fluctuations or the mic itself. This one uses this mic: http://www.cui.com/product/resource/cma-4544pf-w.pdf

 

[PaulStoffregen]

Is the 3.3V input on the teensy considered Aref?

With analogRead, 3.3V power is the default reference, unless you've used analogReference(INTERNAL).

With the audio library, the ADC input object does configure for the stable 1.2 volt internal reference, which results it less noise and interference.