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Help needed for parasite mode for temperature sensors

1670 Views - Created 23/04/2016

23/04/2016

Posted by:
tom57

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Hi,

Actually I am connecting a couple of DS18b20 temperature sensors to the 1-Wire Pi with all three pins in external vdd powered mode.

Now I want to connect a new temperature sensor - but I have only a 2-wire cable available. Reading the specs I am not sure how to connect a DS18b20 sensor to the board in parasite mode.

Do I need an additional resistor for this part of line?
Can I mix both operation modes on one 1-wire board?

Thanks
Thomas

 

23/04/2016

Posted by:
andrew

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Location:
United Kingdom

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Hi Thomas

You should be able to run the DS18B20 in parasitic mode on the 1 Wire Pi.  I have just tested a DS18B20 on a 1 Wire Pi with the 5V pin disconnected and the Raspberry Pi detected it and read the temperature.   You just need to connect the DQ pin on the DS18B20 to OW on the 1 Wire Pi and GND to either GND or RT.

The internal pullup resistor on the 1 Wire chip should provide enough power to run a DS18B20 in parasitic mode and I don't think there should be any problems with mixing both operation modes on the same 1 Wire bus.

AB Electronics UK Tech Support

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