Hi Kev,  in the datasheet I see that DS1820 has a conversion time of 500ms (max) while DS18S20 has 750 (max): this seems the real difference on timing (another is the bit resolution).
 
But 200ms is "typical" also on the DS18S20:  I suspect that these different values (200 to 500ms on DS1820) are also related to the resolution needed.  If you use only 9bit  (0.5C res.) probably 200ms are enough and 750ms are necessary only for the higher resolution (13bit DS1820 - 12bit 18S20).
I'm not totally sure of this, but in other digital Dallas Sensor (1721 - 1775 - 18B20..) the conversion time is proportional to the needed resolution.

regards
MarcoG
  



---------- Initial Header -----------

>From      : piclist-bounces@mit.edu
To          : "PICLIST@MIT.EDU" piclist@mit.edu
Cc          : 
Date      : Mon, 8 Nov 2004 16:38:25 -0000
Subject : [EE] [PIC] Multiple temp sensors hanging of a PIC

> Hi all,
> 
> I've now built a prototype of an 8 channel datalogger I'm designing (albiet with only three channels) and was wondering...
> The datasheet on the DS1820 says typ 200 ms to do the temp to digital converstion but the datasheet on the DS18S20 says max 750 ms. A bit of a difference!!
> 
> I was planning on having 8 channels all with their own 1-wire bus off a PIC pin. (I think this is know as single legged?) I then tell each in turn to start their conversions, I then go back to the first and keep checking it until it is ready to send me data, then check each of the rest in turn, each should have had time to do their conversion and I get all my data back.
> 
> However with the DS18S20 it looks like I might struggle to get a 1Hz sampling rate of all 8 channels!
> If I were to go down the route of analogue temp sensors and then A2D them on an appropriate PIC, would I achieve higher samples rates. 
> 
> I guess in the real work the sensor isn't going to change temp that quickly but even 5Hz would be nice... the digital route has the advantage of noise protection over the analogue method and I'm not even sure of an anlogue sensor and the const comparison.
> 
> Any help appriciated,
> 
> Cheers
> 
> Kev/.
> 
> _______________________________________________
> http://www.piclist.com PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
> 



____________________________________________________________
Libero ADSL: navighi gratis a 1.2 Mega, senza canone e costi di attivazione. 
Abbonati subito su http://www.libero.it 



_______________________________________________
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist