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A while ago I have bought NodeMCU board along with few sensors to play with. I have coded everything, and, when powered via USB, works like a charm. Problem begins, when I try to use my contraption as a standalone system. It works for few minutes, then it starts giving me false readings from the sensors (like, luminosity of few thousands in a dark room).

I am powering the system with (pics at the bottom of the post) AC-DC step down module, 230v -> 5v (1A of current), which then I am stepping down with DC-DC step down module, 5v -> 3v (800mA of current). Using only these two modules, I power NodeMCU and all of my sensors - currently luminosity, temp&humid, motion, SSR (I had led matrix too. I thought that maybe it drags too much current, but no luck there - after disconnecting it I have same problems).

My main indicator that something is not right, is SSR module. It has a built-in diode of the same size that NodeMCU has. It lights immediately as I start the system, and it (it's diode) flickers (it's intensity changes). It does not flicker, when I connect everything through USB.

I have also tried to put 50uF capacitor into the wiring, but no luck either, system is still unstable. What am I doing wrong? Why does the light flickers? Is 1A/800mA not enough power for my system?

Edit: I know what is the cause. I just do not know how to fix it. I just kept my multimeter on for 10mins for both of the step down modules. 5V -> 3V step down (2nd item in the pics below) is initially giving me 800mA, but then gradually losing current (right now it's at 350mA after just few minutes of work). Is there anything I can do here? Or just throw the thing away and look for some other power supply? It's a standard AMS 1117 with some capacitors on it.

Below are the pictures, of my step-down modules and SSR module:

230V AC to 5V DC (1A out) 230V AC to 5V DC (1A out) - back 5V DC to 3V DC (800mA out) 5V DC to 3V DC (800mA out) - back SSR

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The VIN pin on the NodeMCU board can take the 5V directly. Had no problem with that way until now.

What is strange to me is that the current from your 5V to 3V regulator is degrading. The regulator on the board it's self is basically the same (maybe another manufacturer). What may be the cause is that the regulator is overheating and somehow that the effects the output current and/or voltage.

What you can also try is a LM2596 step down regulator. Those are pretty cheap as well and have a good output capacitance. They can deliver up to 3A at down to ~1.3V. Input voltage is somewhere between 40V and your output voltage plus 1 or 2 volts to let it properly regulate. You can use that module to transform your 5V down to 3.3V easily - i've done it so often with it, i lost count.

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Take care how you power the nodemcu. the VU pin is 5v from USB and i am not sure it can be powered with this pin. I do think it is safe to power your device with the 3.3v pins.

does that solid state relay want 5v?

it may be best to put 5v (upto 20v max) into the VIN pin (which goes to the on-board voltage regulator).

  • You still ask a question in the second paragraph. I suggest Check to see if the solid state relay really needs 5V. – sa_leinad Nov 16 '17 at 8:21
  • I am powering the NodeMCU with 3.3v (into 3.3v pins), as I plan on running standalone (non-nodeMCU) esp modules, so need 3.3v there. The SSR takes 5v. – ojek Nov 16 '17 at 9:52

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