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Author Topic: Bi-direction optocoupler for One-Wire DS18B20 temperature sensors  (Read 1350 times)
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South Africa
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Looking to use a number of DS18B20 temperature sensors all linked on the same data line ( with separate power supply - ie.. not in parasite mode )

Can anyone tell me if it is possible to isolate the data line from the sensor to the boards input pin with a 2 way optocoupler ?

If so, what would be the best part number to use ?
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If I've understood it correctly (*and I stand to be corrected as a noob!) you don't need to isolate the sensors with an external power supply. 

You should be able to happily run multiple sensors (in non-parasite mode) in parallel off three wires - shared 5V external on one wire, shared data on another (going to arduino) and shared GND which is tied between the 5V supply and the arduino. You'll still need a 4k7 ohm resistor at the start of the run between data and 5V.

Is there a reason you want to isolate them?
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You should be able to happily run multiple sensors (in non-parasite mode) in parallel off three wires - shared 5V external on one wire, shared data on another (going to arduino) and shared GND which is tied between the 5V supply and the arduino. You'll still need a 4k7 ohm resistor at the start of the run between data and 5V.

Is there a reason you want to isolate them?

It is the shared data to the Arduino pin that I am looking to isolate.  Everything else to & from the board is to be isolated either with transistors, MOSFETs, relays or optocouplers.

With the length of the wires being used, I thought it would be best to isolate all pins.
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Sussex UK / CT USA
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This question relates to answer in...

http://arduino.cc/forum/index.php/topic,58324.0.html

A "bi-directional opto-isolator" is a difficult concept to grasp in this context
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nr Bundaberg, Australia
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There are bi-directional I2C transceivers, maybe they will work.

Also look at the ADUM1200/1201/1250/1251
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« Last Edit: April 19, 2011, 08:09:15 am by Graynomad » Logged

Rob Gray aka the GRAYnomad www.robgray.com

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