Dallas One Wire Driver circuit

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Hi Guyzz

Im going to put 3 DS1820 on approx 30 meter of PDS Wire

I have read in

Dallas Application Note 148
Guidelines for Reliable 1-Wire Networks
http://pdfserv.maxim-ic.com/arpd...

And it seems that they think the "just a pullup to +5v" is for Short Network diameters (Cable lengths).

I was thinking about building the example with the FET , but wanted to hear if anyone here has experience in running 30 mtr (100 feet) using just the pullup.

Btw i am wondering why there is no termination in the "far end" , but guess that Dallas knows best.

/Bingo

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Btw Just stumbled across this Table..

Quote:
1-wire commands vs devices:

http://owfs.sf.net/commands.html

and a simpler version (excludes weird devices like the DS2436):

http://owfs.sf.net/simple_comman...

Hmm a knowm problem with some DS18B20
http://lists.dalsemi.com/maillis...

/bingo

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Hmm could this work ??

Water Depth Sensor
This operates on the principle of measuring the capacitance of a bunch of capacitors, some of which are under water (and hence are [effectively] shorted out). The capacitors form the C part of a 555 timer circuit. This oscillates at a frequency proportional to the number of capacitors out of the water.
The frequency is measured by a DS2423 (counter). Actually, the pulses are counted and the host determines the frequency.

The capacitor chain is connected from two holes in the board. A CMOS 555 is used so that the circuit can run on parasite power. This uses channel A of the counter.