I have a project that uses a Nextion (NX4024T032011) display and an Arduino Mega using a 12.47VDC power supply to Vin on the Mega. The total draw is 320Ma which makes the board reset after about 15 seconds. Oddly, it does not reset if I use the USB port connected to the computer even though it draws the same amount of current.
The Nextion is drawing 103.3Ma by itself so I want to take it off the 5V supply on the Mega. On another note, the datasheet states it should be drawing 85Ma at 5V.
Since the Nextion voltage spec is 4.75-7V, I obviously need to drop the voltage. I've found I can drop to 5.64V using a 66 Ohm resistor. However, when the display goes to sleep, the voltage rises to 11V at 21Ma.
It will never be awake for more than 1 hour and often 15 minutes or less. I've run it in this condition for 2 hours and there's no apparent overheating and the display wakes up and performs nominally when touched awake.
Does anyone know if this will harm the display long term? I'd really like to avoid installing an additional 5V supply. There's not a lot of room in the enclosure.
Any advice will be greatly appreciated.
Thank you in advance
Powering a Nextion (or any display) through a resistor is not a good idea. I can't say if it will be damaged long term but you are exposing it to higher voltages than it is designed for. The voltage becomes dependent on the current drawn by the Nextion, which varies a lot more than you have measured. Have a look at Unsing Nextion displays with Arduino reply #68, there are oscilloscope traces showing how the current drawn varies rapidly. This variation will not have shown on your multimeter, which will have given you an average. Equally, the voltages you measured will have been averages, there are probably spikes well outside the Nextion's maximum input voltage.
Gadgetman9:
Should I solder a 470pf capacitor across the Nextion supply terminals even with a buck converter?
Certainly NOT 470pF!!! 470pF won't do any harm, it won't do any good either.
470μF is what you need. It's not essential however you power it, I recommend it because the Nextion displays generate so much noise, so my answer is I recommend you put one on but it will be fine without. Note that 470μF was found by experimentation, the exact value is not important.
One more question regarding the capacitor. While it may not be necessary, I would like to take your advice and install it. You are far more experienced than myself and I respect that.
Does it need to be right at the nextion power connections, or can I put it on the output of the buck converter? The components are a little tight. I should have bought a larger enclosure, but that's where I'm at. I wanted it to me metal because there are 20A 240V components in the box, too. There will also be two 5V relay modules on the same output.
The idea of the capacitor is to take out the noise from the Nextion as close to the display as possible, which is at the connector. Ideally that's where it needs to be, then the noise does not get into the connecting wires. If you put it further away it will be less effective. However, as it's not essential don't worry too much about it.
I wanted it to me metal because there are 20A 240V components in the box
Do you know that you MUST earth the box for safety?
So you have learned that the on-board regulator on the UNO/ Nano/ Mega 2560/ Pro Mini etc., powering via "Vin" or the "barrel jack" is essentially useless and should not be used for serious projects.
