Go Down

Topic: I think I've got a ground loop messing up my audio. Help! (Read 4 times) previous topic - next topic

scswift

#15
Feb 25, 2013, 10:06 am Last Edit: Feb 25, 2013, 10:12 am by scswift Reason: 1
I only found one viable option for a 3.3mH inductor on Digikey.  That's this one here:
http://www.digikey.com/product-detail/en/AIUR-06-332K/AIUR-06-332K-ND/2343624

Most 3.3mH inductors were really expensive, like $4-$5.  That one is $0.44.  They've only got 930 of them though, that's not a large enough supply to ensure it would be available when I need it.

The 330uH inductors on the other hand are much more common.  I found this one for example:
http://www.digikey.com/product-detail/en/SDR1006-331KL/SDR1006-331KLCT-ND/2127215

A bit more expensive than the above, but still affordable.  Thousands in stock.  And the resistance is 3x lower than the other one.

So I guess using the larger capacitor with the smaller inductor would be the way to go.

[edit]

Actually, this one:
http://www.digikey.com/product-detail/en/AIAP-02-331-K/AIAP-02-331-K-ND/3059883

...can handle almost twice as much current, has half the resistance of the 330uH above, is half as expensive, and is a through-hole part making it easier to use for a patch job.  So I guess that's what I'll use if I have no other option than to add these things to all my LED modules.

scswift

I just noticed you said I could use a low value resistor instead of an inductor.  What exactly do you mean by low value?  1 ohm?  330 ohm?  I assume this has an effect on the frequencies that would be filtered?  I guess the idea is to create a low-pass filter?

It looks like the LED drivers can run at a minimum of 3V.  But I'm driving some white LEDs, so the minimum actually needs to be more like 4V.  And my power supply is typically 5V, but could be as low as 4.5V if running on 3 AA's.  So I guess to be on the safe side I would need to the voltage drop to be less than 0.5V.

dc42

This is the first time you mentioned using AA cells to power the lights. Please update your original diagram to include the light modules and the power to them. Also post a schematic of the light modules.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

scswift


This is the first time you mentioned using AA cells to power the lights.


Oh, no that's not something I'm doing right now.  This board is designed to be used in lots of different props.  It has a built in 3W amp for small props.  In those props the board would be powered by AA's.  There's no noise issue when I run the board that way.  But I do need to make sure if I make any changes to the LED modules that they will still work when the board is powered from batteries.

Quote
Please update your original diagram to include the light modules and the power to them. Also post a schematic of the light modules.


Here's the schematic for those:
http://mightymicrocontroller.com/Mighty-TLC5947-schematic.png

These modules are connected to the LED port on the Mighty via ribbon cables of varying lengths.  They get both data and power over the ribbon cable, and multiple modules can be chained together.  In this particular prop, there are two modules.  The first is attached via a 6" ribbon cable, the second via an 8.5' ribbon cable.

dc42

OK so if the LEDs are running from the same +5V source as the TLC5947s then you should increase the 10uF caps to more like 1000uF.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

Go Up