I need some 2.0 meg and 2.49 meg resistors, 0603, ROHS, 0.1% or maybe
0.25%. The usual suspects, Digikey and Mouser, seem to stop at 1M.Can anybody recommend suppliers?
-- John Larkin Highland Technology, Inc jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
On a sunny day (Wed, 26 Mar 2014 10:38:25 -0700) it happened John Larkin wrote in :
2 x 1M in series?
Too late, the board is done.
-- John Larkin Highland Technology, Inc jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Canted tombstones, touching at the top? George H.
Oh I did some hand selecting of 10Meg 1% ers.. but one gotcha I found was that soldering them into place changed the resistance.. (by 0.1-0.2%) (though hole metal films)
can you squeeze an 0805 in?
George H.
No, the board is under 2 square inches and it's really dense.
(I mean "dense" in the sense of lots of parts!)
-- John Larkin Highland Technology, Inc jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
-- http://www.texascomponents.com/store/VishayFoilResistors.asp
Colorful web site! Do foils go that high? Anyhow, I pinged them on the general requirement. Thanks.
-- John Larkin Highland Technology, Inc jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
The vishay metal foil resistors are not available in the megaohms range AFAIK.
See e.g.
-- John Devereux
Do you have a laser trimmer handy? If so, buy 1M or lower value resistors and trim them up to the desired value. Available in 0603 size: App note:
I used them in various filters but at lower resistance values when we switched from hybrids to PCB construction. Not having to buy or stock a mess of non-standard resistor values was the major benefit. Already having the laser trimmer on site from the hybrid operation was a big plus[1].
You'll probably need some conformal coating to protect the cut after trimming. I suggest an acrylic.
[1] For fun, I also tried the S.S. White airbrasive trimmer (sand blaster). Not recommended.-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
They got right back to me. They can't supply those values.
Mouser has some 0.5% parts, maybe the best I can do.
-- John Larkin Highland Technology, Inc jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
(Rummages around in his desk drawers)
No!
Maybe I could buy a couple of K of the trimmable parts and get some shop to trim them up for me. I could start with 1.5M or something like that.
Actually, I could start with 2M and/or 2.5M and trim *up* a bit. Ratios are what matters in this circuit, not so much the absolute values.
Hey, Jim claimed to have an analytic solution to resistor trimming. I wonder where that is.
-- John Larkin Highland Technology, Inc jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
On a sunny day (Wed, 26 Mar 2014 13:19:47 -0700) it happened John Larkin wrote in :
So.. how about 2 on top of each other, the second a much higher value to get the accuracy?
That would require hand selection. Production would lynch me.
-- John Larkin Highland Technology, Inc jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Put them on edge, diagonally. ;)
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
To get 2 megs from 1 meg resistors, we'd have to make a teepee. 2.5 megs is Stonehenge construction. 5 places on the board.
I'll find out if our pick-and-place machine can do that.
-- John Larkin Highland Technology, Inc jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Nah, I meant fitting in the 0805 that way. I do it manually all the time, because it's much easier to hold the parts edgeways.
Pretty fancy.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
It's interesting that the PnP weighs 5000 pounds, to place milligram parts. We've rented a *big* forklift. Liz and Paulo are planning a forklift race.
I once ran a car into a forklift tines. Slit that Chevy open lengthwise like a can of sardines. That's a whole nother story.
-- John Larkin Highland Technology, Inc jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
-- So you laid out the board with unobtainium parts?
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