Any cheap small log potmeters <50 ohms?

Joerg · 2006-01-24T22:32:35+00:00

Hello Folks,Are there small and cheap potmeters 50 ohms and lower that are log or audio-taper?Reason I ask is that I want to make an adjustable current source out of just two parts, an LM334 and that potmeter. Well, plus maybe a limit resistor for the upper current range (or a mechanical peg on the pot). The current shall be adjustable from about 1.5mA to 8mA. No big deal but with a linear potmeter the upper part of that range is being squished into the last 20% or so of that potmeter, making it kind of fickle to adjust. The current setting of an LM334 is proportional to 1/R.I am looking for one of those cheap transistor radio type potmeters. The alternative would be a more elaborate voltage control circuit but it's larger and also I am limited to very small voltage drops. Can't waste many battery volts in overhead here.Regards, Joerg

Jan 24, 2006 24 Replies

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Frank Bemelman 20 years ago

"Joerg" schreef in bericht news:7WxBf.14170$ snipped-for-privacy@newssvr13.news.prodigy.com...

Perhaps a cheap low voltage sot-23 opamp will do, howland current source, allows you to use any pot you like. LMV321, 21 cents a piece.

Thanks, Frank. (remove \'q\' and \'.invalid\' when replying by email)

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John Fields 20 years ago

I understand. What would you like the the "open" resistance of the pot to be and, say, its resistance when the shaft was at its halfway point around the arc?

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Joerg 20 years ago

Hello John,

Hmm, one of those cases where I couldn't see my own reply. Guess the news server swallows some posts again.

Ideally full open would be 45ohms and minimum 9ohms. But that's not critical, I could use a mechanical peg. A halfway point around 15ohms would be nice. Or less, since the high current values will still continue to cram themselves into the corner from there.

When using a series resistor of 9ohms to cap the max current the halfway point would need to be well below 10ohms.

Regards, Joerg

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Joerg 20 years ago

Hello Frank,

Thanks. The cost would certainly be ok here but the Howland requires a path to ground, or a Hi-Z load sense. Since there is no power switch here it would drain the battery.

Regards, Joerg

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