Any cheap small log potmeters <50 ohms?

The lowest value audio taper I've ever seen is 5k.

Graahm

"Joerg"

** No.

** To operate in the normal clockwise direction - you need a reverse log pot.

For fine adjustment a 100 ohm, 10 turn WW pot will do.

Or just use a 12 way switch and some fixed resistors.

.......... Phil

Hello Graham,

Well, that's where the market is, unfortunately. The lowest log potmeter I have used was 1K and that was a rather large hi-rel version.

Regards, Joerg

Hello Phil,

:-(

That would not be an issue here. It'll be thumbwheel and just be mounted the other way around.

Both way too expensive and too large.

Regards, Joerg

Fake it.

Hello Jeff,

Thanks, but won't work in this case because it isn't a voltage divider. It's an adjustable series resistor.

But that is a great link, it can save some spreadsheet time. In case others are interested in the 'potmeter curve bending' plots here is the link from the thread:

Regards, Joerg

If you let the moving part of the pot carry that kind of current,it will not live very long.(or work very well).

Ah, my old, undeletable website... this bendy pot page seems to be popular

martin

Yeah, the only problem in this case is that you want the resistance vs shaft angle curve to be concave upward, which means you have to use a negative resistance in parallel.

OTOH, you can do this, e.g. you can linearize a platinum RTD

*beautifully* with a little positive feedback. Not much use to Joerg, but oh well.

Cheers,

Phil Hobbs

Idon't know about 'cheap', but the Bourn's 81/82 ranges are available in log taper, down to 50R value, as are the 85/86 range units, but I'm fairly sure these are more expensive.

Best Wishes

In the old days, CTS would make whatever we wanted. Just pop in and have a word with their engineers, place a reasonable minimum order and the stuff would be ready in a few weeks. You can probably still do that- but not in North America.

Best regards, Spehro Pefhany

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Hello Roger,

I am still waiting for a call back from Bourns Engineering. Hopes aren't high though. I remember 50ohm log taper pots for RF attenuators and still have one here. But these were rather huge. Also, with the advent of chips like the AD603 their market might have shrunk too much by now.

Regards, Joerg

Hello Spehro,

Haven't found anything under 100ohms at CTS. Long term if this goes in series production it will be a custom pot. Probably one of those dual paste screening deals like we use with hybrids.

Regards, Joerg

Hello Martin,

Well, then I'd say thanks for posting it. It ought to be popular with people who can still read graphs ;-)

Graphs are so powerful yet since the advent of laptops and PDAs they do not get the recognition they used to. Same with Smith Charts and slide rules. I recently showed a few engineers who do solve a rather intricate problem with a Smith Chart. "Wow, it's that easy?" The only downside is everytime I do that I have to buy a new compass because of air travel security regs. Luckily someone on this NG mentioned those cheap ones for school kids. Walmart has a plastic compass for $1.09 and there always happens to be a store on the way to a client.

Regards, Joerg

Hello Sjouke,

Yes. It depends on the type of wiper. In this app it's not going to need much precision and would be somewhat of a disposable.

Regards, Joerg

It could be worse! One of the older technicians I worked with at Microdyne had to go on a service call to China because they couldn't get some microwave receivers we had built to work for their first attempt at international satellite video links. He was stopped by customs and grilled by government agents as a spy because the front of the Microdyne manuals all had an image of a huge microwave antenna. He told the me that the only thing he understood was "You Spy?", till they finally turned over to someone who spoke english. It turns out that the government's liaison didn't show up on time to meet him, and had contacted the company to ask where he was. It took a while for word to go up the chain of command about the spy they had arrested, and they recognized the Microdyne name in pictures they had taken of the confiscated tools and books.

After all that, it turns out that the equipment had been disassembled by customs, and not put back together properly.

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Can you use a pot with a resistor in parallel with the wiper and one
of the ends of the pot?:


      +-----+  
      |     |
     [R]    +----->ROUT
      |     | 
      +-->[POT]
            |
            +----->ROUT

have a chat with Omeg, they seem to be a small helpful firm that might have a low MOQ

martin