Newbie here.

I'm trying to power a 12 V 4-wire fan and a Wemos D1 Mini from the same power source. The aim is to use a Dallas DS18B20 temp sensor and increase/decrease the fan speed as per the temp range.

Everything works fine when I power the Wemos separately (i.e. via the USB connector) and the fan by a 12 V source, but as soon as I try and run the two from the same power source, I start burning the 18B20 temp sensor.

I suspect a ground loop or something like that - here's a diagram of how I've wired things up:


simulate this circuit – Schematic created using CircuitLab

  • \$\begingroup\$ Hi Calvin. Just a note that you can create a schematic right in the question by clicking the schematic button (or pressing Control+M). On the 18B20, can you label your schematic with the GND, DQ, and VDD pins? Is the connection from Wemos D2 to the fan the SIGNAL (tach or RPM output)? Is the resistor shown in the schematic a 4.7k pull-up from DQ to positive? \$\endgroup\$ – JYelton Jul 22 at 20:15
  • \$\begingroup\$ Start with a list of specs for each interface and setpoint for 100% and 0% fan with linear range between. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jul 22 at 21:33
  • 2
    \$\begingroup\$ @Sunny How does that help fixing the problem with destroying his temperature sensors? \$\endgroup\$ – jusaca Jul 23 at 7:50
  • \$\begingroup\$ Why type of buck converter are you using? It seems to have a seperate - pin for the 3.3V output. \$\endgroup\$ – JRE Jul 23 at 10:59
  • \$\begingroup\$ Ok - I think I owe Jay a big thank you for beating me to that schematic! Thanks. \$\endgroup\$ – Calvin Jul 23 at 15:28

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