thanks for your help. Indded that semms to be a bigger problem with this 18S20. Nevertheless I´m happy that they wotk fine with the Selfmade-Converter and the digitemp Prg. So I knew tht the things are working well and not dead.
Maybe it could be a solution to have a closer look to this converter and to the digitemp program to find a solution for the arduino toohttp://www.digitemp.com/http://public.rz.fh-wolfenbuettel.de/~hamannm/general/digitempd.html
So it works as long as I use 2 of this with the arduino
Ground ---- Ground
Data ----- Pin 2
VDD ------- +5 V
and also a 4K7 Resistor between Data and +5V
Meanwhile I found this info:Note on resistors: For larger networks, try something smaller. The ATmega328/168 datasheet indicates starting at 1k6 and a number of users have found smaller to work better on larger networks.
which means would be the resistor.
Edit: Sun 07.02.2010
I changed the resistor from 4K7 to 1K0 and only one still makes problems (-127 Degrees C) (The sensor is ok - no prob with digitemp). Maybe 1 K are still to much.