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I have a Raspberry Pi connected with two ds18b20 temperature sensors. -sensor1 is fixed on the outside of my garage (distance 20m from raspberry Pi) -sensor2 is just connected in a breadboard near the Raspberry Pi. Everything is working well.

I decided to add -sensor3, located outside and 20m from the Raspberry Pi.

Now when I type: cd /sys/bus/w1/devices

If get this: c0-40a000061005 c2-246056869800 c2-247056869000 d0-008000001000 w1_bus_master1

Instead of: 28-..... 28-..... 28-.....

Each sensor ref should be start with 28-.....

What is happening with my sensors? If unplugged the sensor1, then everything is well. If I unplug sensor3 and let only sensor1 and sensor2 everything is well.

What modification do we have to do when sensor are located far from the Raspberry Pi?

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There is a good tutorial called "Guidelines for Reliable Long Line 1-Wire Networks" that you can Google. It recommends using CAT5 Ethernet cable for your connections. You can find info on driving circuits for the 1-Wire bus by Googling "Choosing the Right 1-Wire Master for Embedded Applications".

Your setup should be able work, given that it does not appear to go beyond the limits described in the first document.

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