tapped trimpots?

Does anybody make tapped trimpots?

What I'd really like is a surface-mount part with lots of taps, not just a ct. Six or so would be nice.

Google is quiet on the issue.

John

Reply to
John Larkin
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Series a bunch ............

Crom

Reply to
crominator

If each tap needs full range - parallel 'em

Crom

Reply to
crominator

All I could find were huge wire wound rheostats. Not exactly surface mountable or miniature.

I have no idea what you're designing, but with lots of taps, it might be easier to switch a mess of fixed resistors, and trim the final value with an ordinary pot. Kinda like a "range" switch, and a "fine tune" pot.

Actually, Google search does talk:

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# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
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Reply to
Jeff Liebermann

I want to delay a digital signal from, say, 0 to 5 ns in one turn of a pot. Ideally, it would behave like a true variable delay line, and not lose bandwidth as the delay increases, and it would delay both edges equally. This implies that it must store more than one bit of information.

So, this sort of works, but of course nobody makes the pot:

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I could use a tiny rotary switch to pick off the course delays, then a simple fine trimpot-based delay generator to interpolate between steps, but it would take two gadgets, and I'd like to put eight adjustments in a small box, and 16 widgets is a bit much.

I recall that somebody used to make a variable delay line, sort of like a wirewound resistor, but they were huge. The programmable silicon delay lines aren't very good... coarse steps, large min delay, bad tc's, lots of jitter.

John

Reply to
John Larkin

John Larkin snipped-for-privacy@highNOTlandTHIStechnologyPART.com posted to sci.electronics.design:

I have seen them with one and two taps. Though i have not seen any for over 20 years. Unless you need about a million of them, they would be considered a very custom part with a corresponding price.

Reply to
JosephKK

John Larkin hath wroth:

I just looked at a linear slide potentiometer in my junk pile. It kinda looks like some silver conductive paste can be smeared on the edge of the carbon area and brought out with a wire. Obviously, this is not a production concept, but it can work for a small number of pots.

It also eliminates using an all pass filter which was going to be my next suggestion. Basically, you have to maintain waveform integrity which means your circuit can't have any group delay and amplitude rolloff with frequency. It also eliminates using a variable inductor coupled with tracking variable capacitors due to the same reasons.

So, that leaves a digital solution, assuming you don't mind regenerating the digital input signal. |------\ in---------------| \ | | NAND O------- Out |---R-----| / | |------/ C | ___ \ /

Yech, but it should work for small delays. Either R or C can be adjustable. A cleaner version could be done with a J-K flipflop, but the minimum delay with substantially larger than with a simple gate.

Got numbers for frequency range? Duz the minimum deleay really need to be zero? That's not easy.

Hmmm, you could build one. Take a soda straw like coil form, and wrap as many turns of magnet wire around the soda straw. Add taps at convenient places. It might work with just a single powdered iron core, moving in and out. However, if it doesn't, break the core into small pieces where the length is about 1/2 the space between taps. The other half, stuff in a plastic insulator. When you move that in and out, you change the inductance of each coil section equally.

I vaguely recall that there was a commercial version of this abomination sold for SSB quadrature phase shift modulator designs. You're right, they were big because they had to work at audio frequencies. I'll see if I can find one, but I'm fairly sure you'll hate it.

Disclaimer: I have't done this for a very long time.

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Jeff Liebermann     jeffl@cruzio.com
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Reply to
Jeff Liebermann

On a sunny day (Wed, 03 Oct 2007 20:50:05 -0700) it happened John Larkin wrote in :

In the olden days *varicaps* (variable capacitance diodes) were used to make a variable analog delay line. And then 2 opposite each other . This was the way to shift couple of nanoseconds to even microseconds in TV. Ampex colortec and amtec time base correctors. So the C in you LC, replace it by varicaps, take signal from end.

Reply to
Jan Panteltje

"Sort of" works, OK, I'll grant you that, but my techie pea-brain is thinking, you can't pick up a fine delay with a pot across a stage of a lumped line - you'd get a signal with two humps - one at point A, the other at point B, with varying amplitude as you go along.

Or am I missing something, as usual?

And anyway, from the hacked trimpots I've seen, it would be almost impossible to construct one without a little dead band on top of each tap, but I'm thinking of wirewound. It could probably be done with cermet or something, but does that circuit _really_ act like an infinitely variable delay line?

Thanks, Rich

Reply to
Rich Grise

Penny & Gile$ may do a custom, or maybe somebody who does those force sensitive resistors may have something.

then I found this

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Martin

Reply to
Martin Griffith

JosephKK joseph snipped-for-privacy@sbcglobal.net posted to sci.electronics.design:

On the other hand if you can tolerate a dip package 10 taps about 1 ns each is perfectly feasible.

Reply to
JosephKK

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