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sensor and communication method

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Full Member level 2
Nov 21, 2003
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Dear Friends:

i need to connect a temperature sensor to a pic, but i have some problems:

1- it is a battery project so i need to consider how much current i "spend" feeding the sensor and the signal condicioning.

2- need 0.5ºC or 1ºC accuracy.

3- maximum distance 20 meters.

4- minimum vcc = 3 v

Any suggestions how to do this?. Any sensor. I saw a lot of sensors with low current, but the interface is spi and i don't thing that i can use spi with a cable 20 meters long!!.

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1-Wire Parasite-Power Digital Thermometer DS18B20-PAR
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The 1-Wire® protocol was originally designed for communication with nearby devices on a short connection — a way to add auxiliary memory on a single microprocessor port pin. Customers soon devised unique applications that involved extending the bus and moving the slave devices farther and farther from the master

Overview of 1-Wire Technology and Its Use
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Guidelines for Reliable 1-Wire Networks
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DS18B20-PAR/DS18S20-PAR/DS1822-PAR Advantages for Remote Temperature Sensing
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I have used that 1-wire thermometer with a PIC and it works very well.

I have three of them on a single bus as part of a solar heating controller. They have been running for about 6 months taking a reading from each sensor every 5 seconds and I think there have only been about 5 bus errors in that time.
I am actually not using the sensors in parasitic mode as I wanted power avalible for future expandability but as far as I am conserned the only problem with the sensors is the cost.


edit: Forgot to say that the closest sensor is on the pcb, the middle sensor is about 15m away and the furthest sensor is about 25m away


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