While stuffing a BOM with Mouser part numbers for a prototype order I found that pretty much all the multi-turn trim-pots were in stock. Except for the transparent ones. None, zip. Arrgh.
How can that be? I was wondering why anyone would want to use a non-transparent trim-pot where you cannot see the position it is in. So the demand for transparent ones should be a lot higher.
-- Regards, Joerg http://www.analogconsultants.com
"So rare. So rare."
Wasn't that a top ten tune hit from the late '50's ?:-)
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
Duuno, but I never figured out why US manufacturers could get away with shipping trimpots apparently set at random from one end to the other. The Japanese ones were always set very close to the middle right from the factory. If your design was good the pot would hardly have to move, since most of the time the variations will (mostly) cancel out. Also helps identify outliers in case something else is wrong.
Best regards, Spehro Pefhany
-- "it's the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
Most designs adjust the pots to some measured parameter, voltage, current, time, pulse width, amplitude, etc. If the physical position is important, why do you need a trim pot? Just use a fixed resistor of the corresponding value.
"Bob Eld" wrote in news:vUYeh.6360$ snipped-for-privacy@newssvr11.news.prodigy.net:
If you need a fixed gas pressure in a pipe and have a regulator, does this mean you don't need a gauge?
The idea of seeing the position of a multiturn pot IS a good one, have you ever tried tweaking a device when direct physical feedback is worth more than the hassle of attaching some kind of metering to do it? If not, then you haven't done much tweaking.
Transparent, unfilled plastic melts too easily. We've had that same problem with surface-mount LEDs; they tend to fail when reflowed, and if you try to replace one, your tweezers just squish them flat when you try to solder them.
The surfmount led's we use now are either on a ceramic substrate, or have a clear plastic inner region and an opaque overmold that can take the heat. Osram has some great side-firing surface-mount led's that are rugged, have great optics, and come in all colors.
But why use multiturn pots? You can see the position of single-turns, and they have about the same working resolution and maybe even better stability.
Last few boards we've done had no pots at all; everything is in serial eeprom or flash. Well, I did use some pots to calibrate gains in a couple of optical/electrical converters. It's surprising what bandwidth you can use a pot at.
John
--- Yup.
Here's a link to a sample:
Andy Williams also did it, but I don't know when.
From another web site, but I lost the link:
"Words ands Music by John Rufus Sharpe and Jerry Herst
Charted in 1937 by Gus Arnheim (# 2) and Guy Lombardo (# 3) and a #
2 hit for Jimmy Dorsey in 1957. Andy williams also did it, but I don't know when.(So rare, so rare) (So rare, so rare)
So rare, you're like the fragrance of blossoms fair Sweet as a breath of air fresh with the morning dew So rare, you're like the sparkle of old champagne Orchids in cellophane couldn't compare to you
You are perfection, you're my idea Of angels singin' the Ave Maria Or you're an angel, I'd breathe and live you With every beat of the heart that I give you
So rare, this is a heaven on earth we share Caring the way we care, ours is a love so rare
(So rare, so rare) (So rare, so rare)
(You are perfection, you're my idea) (Of angels singin' the Ave Maria) Or you're an angel, I'd breathe and live you With every beat of the heart that I give you
So rare, (so rare) this is the heaven on earth we share (so rare) Caring the way we care (so rare) ours is a love so rare
(So rare, so rare) (So rare, so rare)"
-- JF
John Larkin wrote in news: snipped-for-privacy@4ax.com:
There are several clear epoxies that could be used. The expense might be higher, needing a two-part moulding that has to be cemented together, but I think the current construction of multiturn pots isn't much different.
John Larkin wrote in news: snipped-for-privacy@4ax.com:
If you trim the current of a DPSS laser pump diode, the last thing you want is some sticky one-turn pot to jerk through the max current point and fry the diode. I've used both types of preset, and I find it's worth using multiturn types even where single turn types might do, they work much better when setting accurately. I take the point about stability, but I don't think it's any better. Even single-turn pots have spring tension that can upset it after you leave it. With a multiturn you can turn back a fraction to release this, there is enough hysteresis there to allow it safely. Try doing that with a signle-turn pot, and you'll be tweaking for half an hour trying to repeat the same value, let alone make it stay there.
want
that
there.
So, do you set the current in the laser diode by the position of the pot wiper or do you actually measure something? Something tells me you don't use the wiper position as an indicator of the diode current.
I still had to have my diapers changed back then :-)
BTW, Jim, when I answered your 2nd email on Friday it came back with some kind of spam refusal message. Just wanted to let you know since that might also happen with client email.
-- Regards, Joerg http://www.analogconsultants.com
This is for prototyping and we need some fine adjustment capability for experiments. It's a one-off board, basically to see whether the concept I came up with is feasible and recovers nicely and fast enough when kicked in the shins. My designs for production never contain pots or variable caps either (we used to call that "rubber engineering" in the
80's).-- Regards, Joerg http://www.analogconsultants.com
"Bob Eld" wrote in news:mx_eh.28368$ snipped-for-privacy@newssvr14.news.prodigy.net:
No, because I can't see it. Seriously, the Chinese DPSS lasers often have IC names ground off and reverse engineering is made to be difficult, so instead of measuring an exact current when you don't know what it should be, you just note the current position and the number and size and direction of steps taken in turning. A lot of laser adjustments are made this way, being optical so the habit forms.
The point could be debated beyond inanity but there's no denying that basic visual feedback of position of a moving object is a sensible requirement.
T'is excactly the situation here. A laser diode where the delta between smooth sailing and a bzzzt-poof to the tune of a few hundred Dollars is rather small.
-- Regards, Joerg http://www.analogconsultants.com
I caught it right away. I run a self-checking loop because of all the problems I've had with Cox.
Cox is such a bunch of mean-spirited "Cox-suckers" they hung a spam block on my SMTP relay (operated by GoDaddy).
But GoDaddy is owned by Bob Parsons. He'll kick Cox' ass if they do that again.
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
I was already "testing" the back seats of cars ;-)
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
On a sunny day (Sun, 10 Dec 2006 21:11:34 GMT) it happened Joerg wrote in :
I think that is rather strange. I remember Tek scopes with many many many (one turn) trimpots, form after the eighties (lets say nineties), also the digital storage ones. I also remember prof video equipment with even more. Because analog _has_ tolerances, trimpots serve a good purpose. To make it a religion to avoid these at all cost is bad practice in my view.
Can you dump them? I don't know who your telco provider is but good old Ma Bell has been pretty good to me.
It can be worse: About a month or so ago I had all my emails to t-online.de recipients bounce. Then I began to receive some intervention requests from biz friends over in Germany. They didn't get reponses from US vendors. T-Online is a major ISP in Germany. Turned out they had verbatim blocked a whole SBC server and that cut the guys over there off. To add insult to injury a customer rep of this ISP "service" was quite cocky about it IMHO. If I had to run a biz over there I certainly would know which service not to use.
And I am glad I still have a fax :-)
-- Regards, Joerg http://www.analogconsultants.com
Amen! It is somehow a good thing to come back from lunch and be able to verify that nobody had turned the trim-pot.
-- Regards, Joerg http://www.analogconsultants.com
[snip]
Cox is the only cable provider here. Qwest DSL is slo-o-o-ow by comparison.
This wave of anti-spam hysteria is almost as bad as the global-warming hysteria.
Anyone complains the ISP shuts you off... so malicious crap is happening... and I have enemies galore... leftist weenies can't cope with feeling inadequate ;-)
But after a few law suits it'll stop ;-)
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
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