Hello,
I want to control an automatic shutter with a ESP Wemos D1.
To save one plug I want to use the power adapter (DC 24V 1200mA) of the shutter also for the ESP Wemos D1.
From electronics point of view I am a newbie 
Is that possible to simply reduce the the power by a resistence?
Or is there another simple solution?
Thanks & Regards,
Roger
Is that possible to simply reduce the the power by a resistence?
Or is there another simple solution?
No That's not possible. The reason is slightly complicated but the short version is you need to reduce the voltage
using a regulator or dc to dc converter. the LM2596 is very popular.
I would suggest getting one of those . If you know what the Wemos input voltage is you can adjust it yourself
with a meter or ask someone what is the best way to setup the LM2596 for the Wemos and how to connect it.
I'm not familiar with the Wemos so I'll defer that to someone else. If you want to know the reason you can't
use a resistor just say so but it's probably TMI if all you care about is getting it working.
Tell us more.
You can get a ‘Buck Converter’ to reduce voltage.
What you want is a "voltage regulator". The current (Amps or milliamps) probably isn't significant. Are you "powering" anything else?
The main thing is the voltage regulator should be rated for an input voltage of 24V or more and whatever output voltage you need for the ESP (is that 3.3V?).
A switching (AKA "switchmode") regulator is probably a better choice. Switching regulators are much more efficient than linear regulators so they generate very little heat and are less likely to overheat.
Is that possible to simply reduce the the power by a resistence?
No, you can't use a resistor. There is something called a Voltage Divider that can be used to reduce voltage, but they are only good for "reference" or "signal" voltages, not for "power". ...The problem is, the effective-resistance of an active circuit (like a microcontroller or almost anything with semiconductors) changes depending on what the circuit is doing. Just for example, if you turn-on an LED or a motor the current increases (less resistance) and that messes-up your voltage divider "calculations" and reduces the voltage out of the voltage-divider.
Wow so many answers!
I want to use the power of this one: https://www.amazon.de/dp/B004FDUJF4
Wemos D1 needs 5V.
Cool...
I will read and come back!
Thanks so far,
Roger
OK - here I am back again with the result.
The ordered LM2596 arrived on Saturday and yesterday I tested it.
Works perfect!
Thanks a lot for the support,
Roger
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