> Ruben J=F6nsson wrote::
> > Hi,
>> I managed to find the Dallas DS18S20 sensor (on the web,
>> it says DS1820, but I can't find that and somewhere I
>> read that DS1820 =3D DS18S20, is this right?) and also
>> =

>> The DS18S20 is functionally equivalent to the DS1820 except for one poin=
t: The =

> > DS18S20 has a conversion time of max 750ms and the DS1820 has a maximum =

> > conversion time of 500ms. If I remember correctly the DS18S20 is a newe=
r design =

> > with improved performances and it is backward compatible with the DS182=
0 =

> > (except for the conversion time).



I used DS1820 and DS18S20 on a small PIC16F84A logger, years time ago.
Ruben says OK, the main difference between the two sensors is conversion ti=
me (500ms vs 750ms).

However I observed a (subtle) difference on temp. resolution, not so clearl=
y explained in the datasheet..
Both the sensor have a default resolution of 0.5C, but in high resolution D=
S1820 has 13bit, DS18S20 12bit.
I discovered that the COUNT_PER_C register on 18S20 had always the same val=
ue (16), so max. resolution was 0.06 C. and not 0.03 as 1820. =


A (strange?) problem I found was related to the pullup resitor.  A value of=
 4.7K was good enough for 1820 but absolutely bad for 18S20: the result on =
the registers was always 170 000  012  016 (ERROR).
OK, maybe this was due to a problem on my environment test, as I was workin=
g on a breadboard.
I used a lower value (2.2K) and the readings was aways OK and (VERY)steady:=
 I tested n.5 DS18S20 and the max. difference on accuracy was 0.3 C., that =
wasn't bad..

regards
Marco





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