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Forum Index : Microcontroller and PC projects : DS18B20 and Hall effect sensor interface

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redrok

Senior Member

Joined: 15/09/2014
Location: United States
Posts: 209
Posted: 03:58pm 20 Nov 2016
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Hi Paul;
If your using an external 5V power on the DS18B20 there is no need to pullup to +5V.
Just pull up to 3.3V, Probably at the micro end.

Figure 5 in the spec shows how.
DS18B20
Technically you can use higher valued pullup resistors but i wouldn't
recommend this when driving many devices.

redrok
 
Paul_L
Guru

Joined: 03/03/2016
Location: United States
Posts: 769
Posted: 10:42pm 20 Nov 2016
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Hi Duane,

I am powering each DS18B20 directly. I now see that the pullup source is determined by the logic family of the processor and that the DQ output of the sensor is and open collector so it can't source any voltage.

The 4.7k resistor will provide a low enough impedance path back to the filter capacitors of the power supply so that noise transients and hum will not be likely to mess up the digital data.

Thanks!

Paul in Poughkeepsie
 
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