power filter capacitor

Rock Man

I'm trying to put together the propeller education kit using my own breadboard & parts I ordered (not the full kit). I didn't order any caps & so I am missing the .47uf electrolytic capacitor. I have a 1000uf 100V capacitor I am hoping to use for the other power supply filter cap (the board calls for 2 power filter electrolytic caps: .47uf and 1000uf). My question is this: Can I substitute a different sized (electrolytic or other?) cap for the .47uf one? I have so many other in my box (1uf, 4.7uf, 10uf, etc.) I also have bunches of other types but I'm unsure how to read the markings on them. The other ones I have look like little green pieces of chiclet gum with leads coming out of them. The markings on the one that looks promising is: 2A473K - my guess is that these are picofarads & not micro...???

Any help would be most appreciated. I am almost ready to apply power to my board but I'm waiting to hear about these caps. I'd hate to have to pay more for shipping than the actual merchandise I need to buy... Radio Shack doesn't show the .47uf cap in stock either online or in store & I don't know of any other brick & mortar stores around that sell that stuff. Does anyone recommend anywhere online with cheap shipping & no minimum order?

Thanks.
Jeff.

Cluso99

I do not know the kit parts list or schematic, but IMHO the 0.47uF electrolytic is a very unusual part. Are you sure it is not 4.7uF? Are you sure it says electrolytic? The greencap 473K means 47 and 3 zeros pF = 0.047uF.
If it is definately in the power supply then if the above answers are no then: If it is on the same power rail, use the 1uF and it should be ok. If it is after the regulator then use the 4.7uF. This should work and will not cause any problems.

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Philldapill

Go for it. 0.47uF is probably a ceramic capacitor with a lower ESR. This means that this type of capacitor is in there to "catch" any high frequency transients that the larger electrolytics may not "catch". It's always good to throw a couple ceramics here and there around power pins, but the prop should work just fine without them. That's IF you aren't powering any motors and what not.

Add the caps you mentioned, and go for it.

Futurlec.com has $4 flat rate shipping for orders $30 and below. $6 shipping for <$50. It ships from Thailand, and takes about 10 days though...

Rock Man

Wow. Thanks for the quick & detailed responses. The parts list from the parallax Propeller Education Kit labs: Fundamentals on page 25:
201-01085 2 Capacitor, Electrolytic, 6.3 V, 1000 μF
201-04740 1 Capacitor, Electrolytic, 25 V, 0.47 μF

The wiring diagram is here: http://www.parallax.com/Portals/0/Downloads/docs/prod/prop/PEKit_BoxCoverInsert-v1.1.pdf

Thanks again guys. Then I should go with the 4.7uf?

Here's an excerpt from the manual:
The 0.47 μF capacitor should be placed across the 9 V power input if you are using a 6-9 VDC supply
that plugs into the wall, or any supply wire that’s longer than 9 V battery-to-breadboard adapter that
comes in the kit.

Post Edited (Rock Man) : 4/12/2009 2:15:07 AM GMT

Beau Schwabe

Rock Man,

"The 0.47 μF capacitor should be placed across the 9 V power input if you are using a 6-9 VDC supply
that plugs into the wall, or any supply wire that’s longer than 9 V battery-to-breadboard adapter that
comes in the kit." - For this, the 1uF you have should be fine... Be sure to observe the polarity of the 1uF

The two 2 power filter electrolytic caps are actually both 1000uF... I would use something close to those suggested values.

About the "2A473K" ... I'm not sure what the 2A rating is, but the 473 indicates 47000pF or 0.047uF



As far as ordering... aside from ordering directly from Parallax, I have hade great luck with DigiKey and Mouser.

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

Bob Lawrence (VE1RLL)

Re : 2A

Rated voltage (2A : 100VDC, 2E : 250VDC)

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Aka: CosmicBob

Philldapill

Hey, good to know, Bob. I've seen those ratings and wondered, myself.