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Topic: temperature sensors and relais (Read 2 times) previous topic - next topic


Dec 18, 2008, 01:11 am Last Edit: Dec 18, 2008, 01:13 am by bi0m3trics Reason: 1
>an idea how long can be the 1-wire bus in parasite mode?
I've run a bus with two sensors (connected to a DS9490R) around 100 feet using one wire in Cat5E, and had no problems in parasitic mode.

>Is it possible to run multiple 1-wire buses with just one sensor per bus?
I've personally never needed more than 4 ds18s20 on a single bus. I've read of other getting like 5-7,8, and I've seen a post of on the OWFS site (http://owfs.sourceforge.net/WRT54G.html) where someone got 10 of them working on one bus.

This article is a good read too... http://hackaday.com/2008/12/10/parts-1-wire-temperature-sensor-ds1822/

>is it possible to run both the Eth shield and the 1-wire bus?
Depends on which ethernet shield you buy... the (official?) arduino shield uses digital pins 10-13 (SPI) to communicate with the W5100 on the ethernet shield. These pins cannot be used for general i/o, but the rest are open for business. Similarly, ladyada's uses digital pins 2-7 to connect to the XPort...


>Is it possible to run multiple 1-wire buses with just one sensor per bus?

I have done this but not on the Arduino but there is no reason why not.

do i need to program reading from serial or from ethernet

If it plugs into the PC as a serial device that's what it is programmed as. The Ethernet just acts as a physical conduit.

Sheldon Stokes

Careful, those DS18S20 chips do not meet your precision requirements.  They are 9 bit devices, and cover a 180 deg range for a precision of about 0.33 deg.  


Rusty in Texas

Dec 18, 2008, 09:21 pm Last Edit: Dec 18, 2008, 09:22 pm by Fe2o3Fish Reason: 1
Careful Sheldon, that's not how the DalSemi part works.  You don't
simply divide 180° temp range by 9-bits (or 512) to get the device's
precision.  To quote the data sheet:
It has an operating temperature range of -55°C to +125°C and
is accurate to ±0.5°C over the range of -10°C to +85°C.

The 18S20 always reads to the nearest 0.5°C -- that's its default
precision.  Outside that range its precision is still 0.5°C but its
ACCURACY is more like 1.0°C or more depending on how far away
you get from the -10°C to +85°C range.

Now, tricks can be done with numbers from the device's scratchpad
memory to get the precision or resolution down to 1/16°C but the
accuracy is still to the closest 0.5°C.

'agent smith's requirement for 0.1°C precision can be met BUT... does
s/he want precision or accuracy???  There is a substantial difference!
Getting that level of accuracy can be costly and is not obtainable with
DalSemi's current list of temperature sensors.


i have an ethernet shield associated to a freeduino board ,i want to read temperature over the internet , can anyone help me how to connect the three pin of the sensor DALLAS 18B20 directly to the board, is it correct to connect the first pin GND to GND, second pin DQ to analog 0, third pin VDD to 5 VOLT.and what about the full code that i must write in the Arduino Software to get access to the ip and read the temp.

Thank you very much in advance!

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