Use a FET in series with resistor. Control the FET on/off by PWM so FET + resistor will appear as variable resistance (at average). No need for analog correction.
Vladimir Vassilevsky DSP and Mixed Signal Consultant
a a
Hmmm. Make the RH measurement and translate with a half-DAC switching a resistor tree (or maybe a r/2r ivy).
?-)
Often thermistors for this kind of application are measured by alternately inserting them into an RC oscillator circuit with a single precision reference resistor- and a bit of math is applied which cancels out the supply voltage and capacitor value and linearizes the reading. The oscillator frequency would typically be in the kHz to handle the large dynamic range of the thermistor with reasonable resolution at high temperatures, so not so easy to apply this kind of solution.
Your suggestion might work if it was a simple ratiometric ADC reading.
Best regards, Spehro Pefhany
-- "it's the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
how about a carbon pile resistor tied up with rawhide, catgut, or other hygroscopic material
To meet the resistance target it'll probably need a special composition for the blocks, perhaps 90% cement, 10% carbon
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