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From: Grahame Kelly
Subject: Interface Conversion
Date: Sun, 03 Nov 2002 12:18:12 GMT
NNTP-Posting-Date: Sun, 03 Nov 2002 23:18:12 EST
I need to convert 0 to 6.2VDC (measurement) on a board that I am
interfacing a 10 bit ADC too. The max Vin allowable by the
ADC is AVcc-0.4 volts which means 4.94 on the embedded controller
Could someone suggest a circuit that guarantees the Vin to the ADC
will not exceed 4.94VDC, ADC Z impedance is maintained at
50K and the ADC sensitivity/selectivity over the 0 - 4.90vdc range is
I had considered a opto-isolation circuit by a 4N25 but the linear
curve is only about 0.6vdc - too small. Also diode clamping the Vin
to AVcc means that Vin could reach AVcc+0.2VDC - too much.
FET circuit and others again have too small a linear gate voltage
range to satisfy sensitivity/selectivity (10 bit ADC measuring 0-4.9v).
Any assistance greatly appreciated.
Grahame (at) Wildpossum (dot) com
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