to shield or not to shield

That is the question.

This topic is going to take a little explaining;  but I know how much everyone loves my story telling,  just kick back relax and sit a spell; Im gonna take you on a journey!

6 months and $600.00 ago

I found this darling little mp3 player on sale at Parts Express.  Nifty used thumb drive/ SD memory and had a remote.  Works off 5v.  and a line level stereo ouput. Now how was I gonna get that in my car.  They were only $8 or somthing,  so I bought 2 of them.   They are fantastic; except for a couple tiny manufacture flaws (no support what so ever,  and a remote that has more functions than it says it does.  Including a software library that I have yet to figure out.  ,  amazing none the less.

So, coincedentally iSimple makes a aux input for my car,  and the OEM radio I have has a premium CD changer you can get,  yet I dont.  The iSimple device lies (more like teases) the radio and computer to think that it has a compliant OEM CD changer on board,  and i just turn on the mp3 player now installed on my dash.  Perfect.  Especilly the remote feature.  I dont even have to lift my arm to change songs.   And I hve a ton f old SD memory cards from cameras.  and a new 32 gb that has all my mp3's and i can jam out for....like .....forever man!

I built a harness that converts the 3 wire output to dual RCA using a wiring i borrowed from the equipment I use at the studio.  Ballanced TRS.   You have a hot and ground,  and a 3rd wire that surrounds and shields the two active wires from noise.  I did not borrow the imnpediance leveling however as that would require a transformer a couple caps and stuff that really?  i dont need that.  The isimple isnt even a low level input.  and neither is the radio.  But the technique just the same was easy enough,  maybe i could prevent any hum or signal decay.  well it sounds great.  no problems except one.  This device was not made for a car.  and when i use a thumb drive,  it makes some nasty noise and clearly not the way to go.  The SD memory cards are pin drop silent,  and i have no problem just stickin with that. 

The mp3 palyer dosnt have a case,  open PCB and open microprocessors,  usb  plug/  memory slots  bare,  and the back is a haven for anything to get in there and cause mischief.

So how can I shield this accessory that does contribute to the sound sytem,  yet it donent actually eat much of any resources.  I dant have it fused yet,  i need to do that.  I have it hooked up to a switch,  but it makes a hell of a pop when i turn it on,  so i turn it on before i turn on the car,  then its allready made its pop,  and i dont have to endure it through my system.

On my guitars if I experience noise depending on the guitar itself i may go as far as to add foil shielding and a ground plate this seems to help when dealing with passive magnetic humbuckers.  But may have no effect on this player.  I could use a little magnet that is wound around a inch or so of USB cable. I used a USB cabel because coincedentially its 5volts.  and the USB cabel was for a video camera that had one on it,   so i left it.  when i hook it up to the input uf the computer,  no noise what so ever,  frigin genius.

So anyways thats ther story of the little MP3 player that just wants to be part of the cool gang down at the playground. 

Somewhere i heard there is no such thing as sheilding.  what you are really expperiencing is a complex filter.  The interference is still there,  and still penetrates the device,  its just masked by a series of filters,  so you dont hear it.  Kinda like that not - so - fresh feeling that everyone else notices;  but you just seem to be amune to the noise. 

Thanks for any assistance or guidentce,  i know this is a unique idea,  so maybe this will also inspire others to seek.  I want to make a old school VU meter for my sub box.   and a volt meter alarm for the battery and system load.  And strategic areas of lighting where comon mainainence points are.   How are these non sound devices worked into the design of a system,  and how do I manage resouces and prevent system failure.

Be not guided by morality, but rather, integrity.

Not that I see how your ideas are unique... But follow normal shielding procedures - eg, a shield that is only tied to one end etc. Or add caps depending on what the noise is. (You didn't say if the player is battery or car powered.) And maybe it is a impedance matching issue, especially if the unit has an audio out (headphones etc) rather than a line out. "There is no such thing as shielding"? That sounds like another Mythbusters piece of crap (Faraday was wrong!), else out of the mouths of people that obviously have very limited understanding. "Still penetrates the device" - no dudes, that what shielding prevents - shielding isn't used to cut or prevent existing source noise, only its ingress from elsewhere. As to switch pops, that's another topic. And voltmeters, yes, IMO essential and the first step for ascertaining car charging and battery health. But voltage is not (directly) a load indicator, merely an indicator of health or problems (ie, voltage drops).

oldspark wrote: Not that I see how your ideas are unique... But follow normal shielding procedures - eg, a shield that is only tied to one end etc. Or add caps depending on what the noise is. (You didn't say if the player is battery or car powered.) And maybe it is a impedance matching issue, especially if the unit has an audio out (headphones etc) rather than a line out.

Its definately not a headphone out,  The levels just don't match that of one.  There is a software volume to give a little contol to the remote; but far fom a level significance to cause any extreme distortion. With the device volume at 60%;  For example,  I have one hooked up to the 7/8 input of my Echo (soundcard)  and I have the trim set at -10; the gain at -3; and the mains at -6; and the sound is playing right at a peak of -12 to -6.  (thats dB code for sounds pretty good)  It would be nice to have an oscilliscope to measure the wave etc, but unless I was making digital effects or somthing,   that just seems overkill; and my little ohm/ volt meter has 2 settings (working and gabba gabba hey, we accept you, one of us)  Its powered by 5volts.  so battery,  USB cabel work excellent.  In the car I put a big ol resistor in front of the device feeding directly off the radio 12v tap.  According to Gabba Gabba it sits right at 5 volts all the time.  However it could be drawwing more current then necessary.  Its definately just the thumb (usb) drive that does this and ONLY in the car.  I can also hear engine noise and an increase of voltage the kind you hear in sound as you accellerate. Take the thumb drive out.....End of problem.  The fix was easy enough, just dont use the USB port.  But curiosity had already set its trap; and once again i'm sucked in like the Ronco Rotisseree (why can't we all just set it......and forget it)

Its been a productive weekend,  now its time to pay the piper.  Another workweek and a whole new set of Corporate dynamics.  Thanks for all the tips,  MYONUS

Be not guided by morality, but rather, integrity.

I'd advise a voltage regulator instead of a resistor. If its current drops its likely to blow. If it is supposed to be 5V and it is, then its current is spot on. But increase or decrease that current, and its voltage will decrease or increase - hence the voltage regulator, or a USB supply. The noise is typical car electrical noise - alternator etc. A USB supply should eliminate that. So too a voltage regulator with typical input and output filter capacitors (whether bought, or made using a 7805 or LM317 etc).

oldspark wrote: A USB supply should eliminate that. So too a voltage regulator with typical input and output filter capacitors (whether bought, or made using a 7805 or LM317 etc).

I found a 12v to 5v 3A 15watt regulator step down for car.  Do you think that would be still too much amp as this is said to consume 900ma?

for 8 bucks ; is easier than making one,  and i can hook a little 4 port to it to power other devices and mount to dash?

also found a 5 dollar LED voltage meter,  that also suits my needs.  The VU meter I will research a little more.  the DIY kits seem hoaky and cheaply desined.   The VU meters I have are vintage dual pioneer meters from the 70's.  To use them may require something more unique.    Or they may be too old to effectively use.  New ones are cheap, just smaller.

Be not guided by morality, but rather, integrity.

oldspark wrote: A USB supply should eliminate that. So too a voltage regulator with typical input and output filter capacitors (whether bought, or made using a 7805 or LM317 etc).

never mind on the usb regulator,  I have a 7805 here in my parts,  with a huge heat sink already on it.  All i need is a scematic and i can make one for nothin.  I'm going to do some searches see if i can't come up with a design. 

Thanks again

myonus

Be not guided by morality, but rather, integrity.

That was too easy  And quite embarrassing that I didnt think of it.  I have all the parts,  including the little project board.  Hope this helps someone else too; so heres what i found.

Components:

• IC1 = 7805
• D1 = 1N4007
• C1 = 100uF
• C2 = 10uF

Be not guided by morality, but rather, integrity.

No - you can never have "too much Amps". Provided the load(s) have their rated supply voltage, they only take what current they can. [ FYI - the water analogy. Voltage is pressure. Current is "quantity". If you have a small cup connected to the Hoover dam thru the dam wall by a pipe or straw, if their water levels are the same, it makes no difference how many litres or gallons either has, flow will only occur if the water levels vary. If you increase your cup's voltage (water level) above the Hoover's, then your piddly little water (Amps) will fill the Hoover. The moral being, it doesn't matter Hoo or how big you are, we can fill you. I mean... Amps can't "push" into a circuit - it needs a voltage (difference) to do that. ] Just think of headlights and small dash globes. That huge Amperage battery doesn't blow the little lights. That's because each light/load is designed for 12V. [Technically they have the correct resistance to limit the current to what they can handle. Ohm's Law V=IR (or I=V/R etc) refers.] If you have capacity to spare (ie, output current), yes - that can be used to power other 5V loads. As long as the total current required does not exceed the regulator's output spec. If it does, it may shutdown or be damaged, but it will certainly decrease its output voltage. (And it may get warm or hot when running near max load.) And VU meters... I've seen some snazzy dual-meters thru eBay or google (google "vu meters" and select images) though I wondered if LED or other bargraph displays were better. On one hand IMO there's nothing like a good classic VU meter. On the other hand, I like the timed "peak hold" function that some bargraphs have, and especially that their reds are easy to notice - even when not directly looking at them. (Maybe a meter with added yellow and/or red peak LEDs? PS - This reply was for your 3rd last reply. I blame 2 telcons for my delay.

IC1 should be f.ex a 7805T (TO-220 package) that can handle up to 1A. Not the smaller versions...

oldspark wrote: IC1 should be f.ex a 7805T (TO-220 package) that can handle up to 1A. Not the smaller versions...

okie dokie,  had to get the magnifying glass out.  Ever since that night withe the shots of everclear...well these eyes jest don se so good. 

wth??   who made these dardish things mini robots form Zargon!?

ok its a UA7805C (previous just a typo)  and its definately a TO-220

looks like Texas Intruments logo and some other numbers 33A61H9

even if I have to buy a 2 dollar VR Im still gonna use this fancy heat sink the size of my .....ummm... thumb.

been working on the wiring of the Amp Rack.  I feel like I acomplished absolutely nothing today o this.  So Iz gonna have me a Fat Tire. And ponder the time I was light years away, makin sweet somthin to the ladies of Zargon.........

Until next time,  Live long and wear a condom.

MYONUS

see down there, next to the bottle cap? Thar be a golden ticket (the heat sink of course)

Be not guided by morality, but rather, integrity.