ESP8266 Temperature log

[xeorex]

Looking at the project here:
https://www.electronicspoint.com/threads/esp8266-temperature-log.286465/

I took the information scattered a bit everywhere to get to this point.

My first question would be why they'd add a 4.7k resistor between the temperature sensor middle pin (data) and the current (last pin) I see on some similar project. Not all do it.

 

[Harald Kapp]

why they'd add a 4.7k resistor between the temperature sensor middle pin (data) and the current (last pin)

Because the datasheet says so in figure 3 accompanied by the following text:

The control line requires a weak pullup resistor since all devices are linked to the bus via a 3-state or open-drain port (the DQ pin in the case of the DS18B20).

. Withoutthis resistor the data line would be undefined instead of high.