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DS18B20: Influence of supply voltage on temperature

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Tigs62
(@tigs62)
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Joined: 1 year ago
Posts: 21
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I have a project using an ESP32 board and five in number DS18B20 Temperature sensors.
Most tutorials say to put a 4.7K resistor between the sensors Vcc and Data pins.

I have found that if I use the 3.3v line on the ESP32 board to supply the sensors Vcc, I get a different temperature reading from my five sensors than if I use the 5v line for their Vcc.
The difference is about 1 degree more for ALL five sensors when I increase to 5v.

I found another forum where someone discussed this same problem in 2019:
https://forums.raspberrypi.com/viewtopic.php?t=240536  

Apart from the majority of "genuine" reply's, there were also a number of "unhelpful" responses from people I felt.

To try to offset any of the same comments/questions, let me just highlight a few things in my experiment.

1.   The 4.7k resistor is on the breadboard  (nowhere NEAR any of the sensors)
Therefore the resistor is not heating up the sensors in any way....at all.

2.   Each of the sensors are 1 metre apart, but they are all in the same room.

3.   None of the sensors are sat on a radiator or in a fridge or are "sat on" by any sort of pet.

4.   All of the sensors were bought at the same time from the same supplier and appear to be from the same batch as the serial numbers are concurrent.

5.   Yes, I have looked at the Dallas datasheet and I know that the temperature reading should not be affected by the change in Vcc as long as it is in range.  However, this does not change the fact that they ARE affected by the change in Vcc.

I found one single reply on another site where someone suggested that it was possible that the sensors, which were bought from Banggood like mine were, might possibly be "fake" sensors, not manufactured by DALLAS.  I am beginning to suspect that this may be the case, because there were replies to the post above from people who replicated the experiment and did not have the same issues, suggesting that the sensors themselves were at fault and not the poor person who asked the question.

My questions are:

Q1:  Has anyone else experienced this problem?

Q2:  Can anyone recommend a site where I can buy "genuine" DALLAS DS18B20 sensors?

Thanks

You are never too old to learn.
You are never too old to teach.


   
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