I try to Power my nodemcu using a Diode to prevent the onboard Regulator from powering the rest of the Board while programming over usb.
Diode is a 4148, i can measure resistance in one direction so it seems not to be broken to me.
I get 3.3v before the Diode as expected but 0v after the Diode.
What am i doing wrong? think its something stupid 
Thanks in advance for your help
Hi,
That diode has a voltage drop of 0.72V, which would result in a output of 2.58V. Also, it can handle max 300mA before it blows. Depending upon how your'e using your nodemcu (using the WiFi takes a lot of power), that may not be enough. I'm not sure why it's reading 0V though. Try taking the nodemcu off and testing the voltage output from the diode.
Sorry, doesn't make sense at all.
Have another go at explaining what you are trying to do! 
Thanks for mentioning the Voltage Drop, I wasn't aware of it ,should have read the data sheet more carefully.
I was totally confused with getting 0v after the diode. Without the nodemcu the diode shows the same behavior meanwhile I think it is broken after all.
You're right. I should have explained the whole setup from the start. Maybe there is a better solution for my probem.
I have a Nodemcu that drives a servo and gets data from a few sensors. To power everything i use an LD33.
This setup works fine until i use the usb port of the nodemcu to upload a sketch or get serial data. I always cut the Power to the LD33 when doing this because i don't want 2 power sources (thats a bad thing right ?)
if i then connect the USB the nodemcu onboard regulator tries to power everything and fails because it can't handle it (nodemcu doesn't boot properly, cant even upload a sketch ). I fix this by disconneting the nodemcu 3.3v Pin from which i get power when not using usb.
What i hoped to achieve was that power can go to the nodemcu but not from it to the rest of the components.
Hi,
A diode sounds like the best idea, but that means you would have to have a input voltage of roughly 4V. The nodemcu only works down to about 3V. I'm not sure what your circuit is, but if you use the VIN pin, you can use 5V - 10V. Could you either keep it USB powered, or just 3.3V pin, and disconnect that pin for uploading? It does sound like your diode is burnt.
Hi,
Those diodes are glass and bending the leads that close to the glass encapsulation can fracture it.
Try bending at least one hole back from the diode, even clamping the lead at the body and bending the lead, the clamping protecting the glass.
Can you post a picture of the other side of the board please?
Thanks... Tom.. 
Thank you for your answers.
I've thought and believe now the best option for me is to power the nodemcu from the Vin Pin (I supply 9v). This way i can cut the 9v and plug in usb without powering the Sensors/Servo or am I missing something?
Hi,
I would assume this 
is a voltage regulator? That circuit looks correct and should work just fine. Good luck!
Where do you get the idea that it is acceptable to power "Vin" on the NodeMCU with 9 V?
Mostly from the datasheet of the AMS1117 that says 12v is ok. Absolute max is even 15v.
Please explain why im wrong.
Have you examined the datasheet of the CH340 (paragraph 6.1)?
As far as i can see the vin isn't directly fed to the CH340D. VDDUSB is protected by a diode (1.0 version of the Nodemcu).
So this shouldn't be a problem ?
Probably not if you have the CP2102 version you cited. Thanks for the reference which I could not find previously.
I was referring to the CH340 version (0.9) so it depends which one you have. Bedtime for me now, sometime later tomorrow I may find my specimens and see which chip they use. 
You're right! thanks for pointing that out.
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