In my more slender disciplined days I ate 6 almonds for lunch... then walk a few miles.
So while my troops had headed out to McD's or whatever, I'd roam the labs seeing what they were up to.
The most fun I ever had was checking out a junior engineer's breadboard.
He had complained of strange behavior before he left for lunch.
I found the mis-wire and fixed it.
When he returned from lunch and fired up his breadboard he was very befuddled.
I didn't tell him for two hours ;-)
...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.
Bad practice? In mass production is isn't just good practice, it is the only way. A good engineer designs circuits so that anything with tolerance is either servoed out or there is some other kind of automatic adjustment scheme that is fully electronic. uC, discrete sampling plus digipot, whatever is cheapest. Trim-pots require skilled production personnel which is usually not a desirable situation in a business. They are also a major source of reliability problems which is not at all desirable. Therefore, this design is like usual. I made sure all of the pots are running in voltage divider mode and none is in a hot feedback path. So they all can and will be replaced with (cheap) multi-channel DACs in the final phase.
Talk to any production manager. They'll tell you that they ideally want to see only this at the final stage of a line: A red lamp and a green lamp ;-)
Really? Check it out at neighbors who have DSL. A lot has changed. I am on 1.2Mbit/sec DSL and they asked me whether I would like to revv that up some so I can watch IPTV. I declined because all I need is fast download of PDF data sheets and you really don't need more speed because the sources are often slow. Missy Bell is pretty fast these days and a lot more reliable (they used to botch DNS lookup around here).
--
| 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 worked for Racal-Milgo in the 70\'s, and one of the things we were
never allowed to do was to let pots leave the premises. I learned a
lot about slop and how to keep it from biting you in the ass back
then.
--
| 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.
19mm mulitturn pots work much better than 3/8" multiturn pots, which I detest and avoid wherever possible. Back in the 1980's Vishay sold a premium 19mm pot at about four times the price of regular parts, with a multi-leaf wiper and other nice stuff.
I put one on one of our trickier-to-adjust boards, and got popular with the technicians who did the setting up, which went much more quickly with the new pot, and the accountants who saved a lot more on the quicker setting up time than we paid for the high-resolution trim-pot.
--
Bill Sloman, Nijmegen (but in Sydney at the moment).
On a sunny day (Sun, 10 Dec 2006 21:59:21 GMT) it happened Joerg wrote in :
Sorry Joerg, my English, but I mean sort of Die Hard (probably not right either), let's say an extremely difficult way to do something. I _KNOW_ about large production runs and the cost of calibration. It all depends on what you do, in the case of Tek scopes (I have worked there) calibrating a scope (from the book) involved somebody doing a _lot_ of adjustments. I have done that, and I have done QC for them too, and repaired the stuff. One could argue that bending a wire to the deflection plates would require re-calibration I have seen them fine tune that way, mm maybe I did it myself some time ;-) (100MHz analog 1Gs digital sampling scopes, forgot the number). You can hardly say Tek made (makes) 'rubber products' or 'rubber designs'. Their equipment is the reference for a lot of things!
Yes you can make accurate stuff at lower frequencies with opamps and tolerance is either servoed out or there is some other kind of automatic
Not always possible or even desirable.
Yes for 1 million mp3 players you are right, not for the sort of things small specialised companies maybe sell at the most 100 of, and calibrate in house. Also not for the big ones who have some standard to go by, and have the environment and qualified personnel like Tek.
This is true, I remember a group going to do preventive maintenance on a couple of million $ pieces of video equipment, and re-adjusting all trim pots. However there were very few problems related to trimmers, these things are reliable. Replace if kaput. There are bad quality ones too.
You can use DAC as digital poti for signals too, I have done that.
Sure, add a blue lamp and you get white light you can read by ;-)
BTW I just heard that per December 11 (as of today) the Dutch analog TV stations are now completely switched off. I dunno about the situation in Belgium, but analog is now officially dead here. You can now buy a digital settop box but I just looked and it said: 'Sold out'.
So who is still using trim pots these days? I haven't put a trim pot in a design in 10 years. Whatever trimming needs to be done is handled by adjusting a gain in software, or possibly with a digital pot. Occasionally I'll tack one into an early prototype to debug hardware, before the software is running, but that's about it.
Trim pots just seem like a way to get on the bad side of your manufacturing guys.
In my chip designs I often design-in potentiometric DAC's that are linear in dB'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.
Maybe global warming is just due to drifting trim pots ?:-)
...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.
Wouldn't you think that for some mass-market products (made in China) it actually is cheaper to have a few trim pots than lots of precision components?
I was just noticing yesterday that a ~decade old JVC stereo I have has a little trimpot on the CD player's laser PCB...
Trimmer caps seem a little more difficult to get rid of than trim pots... even in stuff like reasonably high volume commercial filters, you still see the occasional trimcap. Most cavity and waveguide filters sold commercial also still have visible tuning rods, except on the highest volume items just as satellite TV receivers.
I'd like to see someone build a trimcap that changes the ratio of Ca/Cb while simultaneously being "tapered" such that Ca || Cb is constant -- that'd be the perfect tuning device for a tapped-capacitor matching network.
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.