Re: How to give specific range of resistances?
- From: Tom Bruhns <k7itm@xxxxxxx>
- Date: 7 May 2007 16:17:59 -0700
On May 6, 2:53 pm, Michael <nleah...@xxxxxxxxx> wrote:
Hi there - I need some odd valued potentiometers. I have two different
setups I need:
one that ranges from 178.2 - 207.1 ohms
and
one that ranges from 96.3 to 168.6 ohms
So - my first inclination was to just use a single resistor for the
smaller value and a potentiometer to cover the range. So for the first
I'd need a 178.2 ohm resistor, and a 28.9 ohm pot. However - 28.9 ohm
pots seem to be slightly less common than I would like. Same goes for
the second setup and the desired 72.3 ohm pot. Now - I can fudge
around on these values a bit - but not too much. These values are
setting the output voltage of a light, and if that voltage goes too
high I suspect the magic smoke of the device will be released.
So - any suggestions? I don't need very linear operation from the
potentiometer, if that matters. I don't think many pots have
mechanical stops to stop you from setting the value too high. What do
I do?
Thanks!
-Michael
As an alternative to adding a shunt (parallel) resistor, just put
mechanical stops on the pot.
If your tolerances are 10%, it's a bit silly to be giving resistor
values to 0.1% --
One might suspect there's a better way to do things. Can you tell us
more about the application?
One thing to beware of with potentiometers is that the wipers
sometimes fail to make good contact with the element. In that case,
the resistance goes to "infinity" or at least some large value. It
can be worthwhile when you want a rheostat function (a variable single
resistance) and you have a potentiometer (a resistance with a variable
tap point) to tie the wiper and one end together. Then the resistance
will normally only jump to the end-to-end value if the wiper fails to
make contact properly.
Beware about DC current through the wiper. Some pots handle that
gracefully, and others do not. Wire-wound pots are probably OK.
Cheers,
Tom
.
- References:
- How to give specific range of resistances?
- From: Michael
- How to give specific range of resistances?
- Prev by Date: Re: OT: Dilbert May 7, 2007
- Next by Date: Re: French politics
- Previous by thread: Re: How to give specific range of resistances?
- Next by thread: Instantaneous "on" FET
- Index(es):
Relevant Pages
|
