Isolated variable resistor function?

Oh nonsense! Some things are so simple that reinventing them costs less than looking them up. OK, so it's been done before. So what?

Jeroen Belleman

Bill, think back: 35-40 years ago there was next to nothing in search functionality, other than a massive card registry. You had to plow through zillions of publications because the categorization in the paper card registry was mediocre at best. To top it off you had to order whole stacks from other libraries, only to find out that it wasn't what you thought in there.

This produced some sad results. The worst was a Ph.D candidate at an ivy league place who, years into his work, found out that someone in a far away country had already researched out the very same topic. It had been published in a foreign language that nobody at that institute spoke. In Germany this pretty much meant "game's over", regardless of reason.

Absolutamente. That's how I also see it. You only have to watch the patent area because that can cause things to hit the fan. People patent the most mundane stuff these days and examiner let it pass. Which is why I have an IP disclaimer in my standard agreement that is not negotiable.

Happens all the time. Almost 10 years ago I was very unhappy with the gable diverters for metal roofs. So our roofer and I designed a new type, on the hood of his Chevy truck. It performs much better than the stock stuff. A few month ago I saw the exact same design from a vendor in Europe. Couldn't believe it. But ... so what?

--
Regards, Joerg

http://www.analogconsultants.com/

snipped-for-privacy@ip-64-139-1-69.sjc.megapath.net

We use a lot of the Fujitsu FTR-B3G type parts. DPDT, surface mount, available as latching or not. NEC and Omron have drop-in equivalents. As an analog switch, they blow away any CMOS part on everything but switching speed. Capacitances are sub-1-pF, Ron a fraction of an ohm, holdoff hundreds of volts, bandwidth GHz, isolated drive.

--

John Larkin         Highland Technology, Inc

jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser drivers and controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro   acquisition and simulation

Well said Joerg. Thank you.

I actually hadn't heard the term "Manchester" when I designed the supervisory stuff. We called it "biphase" coding. I don't know how long I'd have had to spend in the mediocre Tulane library looking for something that I didn't know existed and that I didn't have the accepted name for. It took a lot less time to simply invent it.

I considered using 1/3:2/3 pulse width coding, another self-clocking scheme, but the biphase was easy. By sampling each bit twice, biphase gave us an additional error check for free.

You're right, I had a lot less reverence for academic protocols than you did. I wanted to learn basic physics, circuit theory, electromagnetics. Frankly, I knew a lot more about actual circuit design and system architecture, the "electronics" stuff, than most of (all of?) my professors. The Dean of the EE school, my advisor, couldn't understand my senior project, "The Tunnel Diode Slideback Sampling Oscilloscope." He was a tube guy, never comfortable around transistors; he even pronounced "transistor" funny.

You may enjoy insulting my academic credentials, but I have a job, and you don't. Sounds like I used my university education a lot better than you did.

You seem unable or afraid to do anything that hasn't been sanctioned by some authority. How boring.

The supervisory control systems were pioneering, which is why a little company in New Orleans sold so may of them, all over the USA.

The Manchester references there are from 2002 and 2004.

--

John Larkin         Highland Technology, Inc

jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser drivers and controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro   acquisition and simulation

More fun, too.

--

John Larkin         Highland Technology, Inc

jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser drivers and controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro   acquisition and simulation

*WHAT* ?!

You hadn't heard of Manchester United?

:-)

[...]

--
Regards, Joerg

http://www.analogconsultants.com/

The name came from Manchester University... they used the scheme in

1943... but, as near as I can determine, "biphase" existed before that. ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
I love to cook with wine.     Sometimes I even put it in the food.

y y

d the

.

=A0 =A0 =A0...Jim Thompson

And some things look that simple, and aren't. When you look them up you find out about the less obvious gotcha's.

You can save money by skipping the literature search, but every now and again it costs you a lot more than you save, sometimes just in paying royalties to the guy who invented and patented before inspiration struck you.

-- Bill Sloman, Nijmegen

More often, you find a circuit in RSI or somewhere and discover that it's fundamantally unreliable: beta dependent, bad corner cases, stuff like that. RSI is better read for amusement than guidance.

You make up stuff like that. s.e.d. is populated by a lot of lurkers who don't actually design stuff but pontificate on how it should be done.

--

John Larkin         Highland Technology, Inc

jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser drivers and controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro   acquisition and simulation

Too true, which is why instruments papers are wayyyyy below the salt in academic circles. I wrote one RSI paper early in my career and then wised up.

Gizmo-building is sort of like cooking--it's close enough to everyday life that lots of folks have opinions worth listening to, and there are lots of people who are good enough to make up recipes of their own. What's original about Aunt Millie's meatloaf recipe? Who cares? It tastes great, fills the gap, and reminds us of good times.

More to the point, it can be made from the ingredients at hand, and doesn't blow the budget.

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
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net

I could never explain to my mother, or to my wives, what I really do. I just buy parts and connect them to one another. People pay me to do it, 5 or 10 times what the parts cost. It really doesn't make sense.

--

John Larkin                  Highland Technology Inc
www.highlandtechnology.com   jlarkin at highlandtechnology dot com   

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME  analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators

In article ,

My scope makes occasional clicking noises as I change the vertical gain.

I assume that's because somebody decided that relays worked better than whatever else they tried.

--
These are my opinions.  I hate spam.

OK, thanks. I use a fair lot of Pickering Series 103 reed switches myself, and sometimes the parasitics get in the way.

Regards, Jeroen Belleman

Well, yes! If you compare ON resistance, control signal feedthrough, and OFF isolation with your typical MOSFET switch, relays win with ease. If you also consider lifetime, switching speed, size and parasitic L and C, the picture is not so rosy, alas.

Jeroen Belleman

sory

d by

nted the

oks.

=A0 =A0 =A0 =A0...Jim Thompson

he

ots

You are telling me this? I've now published five critical comments in RSI, pointing out where their refereeing process had failed - in 1972,

1996, 1999, 2004 and 2009 - and they rejected similar comments I submitted in 1980 and 1995.

Nobody is saying that every academic paper is to be relied on, but rejecting the whole of the scientific literature because some of it is flawed rather misses the point. We make progress because some of the papers that get published reflect dramatic steps forward.

Larsen N T 1968 Rev. Sci. Instrum. 39 1=9612

is difficult to fault. If you'd read that more for amusement than for guidance you'd have missed quite a bit

What makes you think that?

Perhaps. I'm not actually designing much stuff at the moment, but I've done enough design in my time to be able to talk about the process.

You certainly pontificate about stuff that you have designed - not all that expertly, though do you seem to be tolerably good at eventually finding and correcting your mistakes - and on any number of other subjects where you are much less well-informed. You would yourself seem to be a prominent part of that population.

-- Bill sloman, Nijmegen

visory

wed by

vented the

books.

=A0 =A0 =A0 =A0...Jim Thompson

the

lots

Sturgeon's Law says that 90% of everything is rubbish, and the papers that get published in RSI=A0don't do any better. The remaining 10% can be very useful.

This doesn't explain why the instrument literature isn't highly regarded. The rest of the scientific literature has a similar ratio of dross to treasure. The instrument literature reports what ought to be practicable solutions to practical problems, and science is - in the end - about building theories. Testing those theories is the process of murdering beautiful theories with mundane facts, and that side of the business is just less glamorous, if no less important.

Physicists aren't known for economical circuit design - they persistently use more expensive parts than they need to, and often use obsolete parts long after better components are freely available. My

1996 comment took a couple of RSI authors to task for waxing lyrical about the speed advantage of of 10K ECL over TTL at a time when ECLinPS was freely available and offered a similar speed advantage over 10K.

-- Bill Sloman, Nijmegen

I haven't found reeds to be reliable. And they have nasty thermal EMFs and bounces and electroacoustic twangs. And they are big. We've used about 15,000 of the Fujitsu parts so far, and they are very reliable. The latching versions have no measurable thermal EMFs, so are good for thermocouple circuits and such.

The DPDT Fujitsu parts average about $1.50 each.

--

John Larkin                  Highland Technology Inc
www.highlandtechnology.com   jlarkin at highlandtechnology dot com   

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME  analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators

Joerg,

i don't remember if this part was mentined in this thread, but here it goes anyway.: H11F1M

General Description

The H11FXM series consists of a Gallium-Aluminum-

Arsenide IRED emitting diode coupled to a symmetrical

bilateral silicon photo-detector. The detector is electrically

isolated from the input and performs like an ideal

isolated FET designed for distortion-free control of low

level AC and DC analog signals. The H11FXM series

devices are mounted in dual in-line packages.

Thanks, Jure Z.