room temperature (300 K). If that's correct, I'd go with a 2k
resistor fed from 5 volts and a 0.1 uF cap for noise filtering:
+5V----2k---+---LM335----gnd
|
+---0.1uF----gnd
|
|
A/D input
Use a ten bit A/D object and see how that works. If it's OK, we can
ramp up the accuracy next.
At 05:00 AM 9/14/2007, dickydodds wrote:
>Guys,
>
>I am having a bit of trouble interfacing an LM335 to the Ooopic ADC
>lines and wondered if someone has already been here and got a circuit
>which works.
>
>I cant seem to get a reliable reading or a precise enough measurement.
>Even if I try to use the extvref line with a voltage as low as 4 volts
>(which deosnt seem to make a difference) - I just cant seem to get a
>correct reading. It deosnt help that the oopic cant do floating point
>math.
>
>Deos anyone have a suitable circuit that would allow me to read up to
>5 lm335 temp chips but with some sort of op amp subtractor, say, to
>remove 2 volts so I can more or less read the true temperature
>directly, or at least make a eeprom lookup table to get the correct
>values?
>
>Any help, thought appreciated.
>
>I have tried both firmware Version 1 and 2.2+ on Oopic 2's.
>
>Cheers,
>dicky
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