Firstly I am a systems engineer by experience, a mechanical engineer by education, my understanding of electronics isn't great. I am building something to help my daughter and a bit confused.
I have a 3.5" Nextion (NX4832K035) running off an arduino nano (not every) which is all on a breadboard and powered via the usb into the nano. The nano is connected to two easydrivers to use multistepper co-ordinating two stepper motors. The adruino is powered via its USB and the easydrivers have a seperate 19V supply.
This all seems to work.
I've printed a box to put the electronics in but conscious that the easydrivers can get quite warm so I am putting a small fan on the side of the box. I was going to power the fan (0.1A) from the 5V out and thought I would check capacity on the 5V out from the nano (adjacent to A7 on the board).
Googling the nano 5V output and looking in this forum shows anything between 50mA and 500mA (I think that 's the output of the regulator for all 5V inc outputs(?). The Nextion Screen data sheet says it draws 145mA, and that is working off the 5V output?
I am basically asking can I put the fan on the same power output as the screen? Would the nano cope powering both in parallel, am I asking for noise trouble on the screen putting them both together?
And finally, am I just getting this all wrong? To my inexperienced mind I should maybe add a separate supply DC-DC from the 19V bar down to 5V and power the fan and the screen; unless someone on here tells me I don't need to?
Some things to consider:
No Arduino should be regarded as a power supply, it is a micro-controller, not a power supply. That said, you can draw modest amounts of current from the 5V pin. The big problems arise when you power an Arduino from more than 5V and rely on the on board regulator to give you 5V. The on board regulators are puny and don't have a big enough heat sink, they get hot, they shut down.
If you are powering through the USB connector then you are limited by what the USB port can supply, but also be aware that long USB cables will introduce some voltage drop, especially for large current (Ohm's Law).
Don't rely on manufacturer's data for current / power consumption, measure it! I have just measured 215mA as the supply current to a 4.3" Nextion, so maybe 145mA is reasonable, but check. Also, when I was first experimenting with Nextion displays I found they generated a lot of interference, I first noticed this when I had a GPS receiver that wouldn't work near one. If you've seen my tutorial you'll see I reduced this with a capacitor across the supply at the Nextion power connector, I suggest you do the same.
Breadboard is great for experimenting, crap for a finished project. You should build your final project on a PCB or strip board or perf-board.
If you have a 19V PSU it makes sense to get a buck converter with a 5V output and power all your 5V kit from that. At the very least include one 0μ1 capacitor across the supply as close physically as possible to the power pins of each device.
Powering things from an Arduino comes up often on here, do some searching for more advice.
The fan current is the average current ? Then it draws more current when it starts.
The Nano has a diode from USB_5V to 5V. That is already a voltage drop.
The odds are against you, so I agree with PerryBebbington.
I checked it all worked on a breadboard and am now rewiring it onto strip boards that look (to me like mini "naked" breadboards?).
I will add a PS board from the 19V, seems like that makes sense and will check my box of capacitors thanks again (is there a tolerance on the capacitance, genuinely no idea what I have sorry) for the screen.
I have a few of the small yellow capacitors with code 104 on I believe these are 0μ1 so I am ok for them thanks.
On your tutorial you showed a 470μF capacitor across the Nextion power in lines, the largest capacitor I have is 100μF sorry to have to ask but should I put the 100μF across or put nothing now and wait until I can get the right component as getting supplies at the moment is very time consuming (or expensive). I've tried reading as much as I can on here about decoupling capacitors but the potential consequences of a substitution of this type very quickly gets beyond me.
Am I also missing a trick as I am using two Easy Driver boards with a 19VDC input, each of them has a 5V output, should I be using this to power the screen/fan/arduino nano rather than add another supply? The Sparkfun website has a slightly confusing statement on the 5V output "5V -Output. This pin can be used to power external circuitry. 70mA max is required for Easy Driver functionality"; at first I thought this meant 70mA was the max output but I now think it means the driver uses very little power so there's lots of spare capacity?
That's it. Thanks again for your time and knowledge and sorry if this is elsewhere and I just can't find or understand it.
That's where I got the information from thanks, and also thanks for confirming not to use the easy driver 5V out as a power supply. I've ordered some buck convertors that I can wire into the 19V input but they won't arrive for a week and I am keen to get on. Temporarily I will be using a 12-5V board I already had to check it all works thanks I don't want two power leads as I have already made the box (sad but true).
On your tutorial you showed a 470μF capacitor across the Nextion power in lines, the largest capacitor I have is 100μF sorry to have to ask but should I put the 100μF across or put nothing now and wait until I can get the right component as getting supplies at the moment is very time consuming (or expensive)
470μF was found by trial and error using a 7" capacitive touch screen Nextion and an oscilloscope to monitor the current spikes, see the traces on the tutorial. 470μF was the lowest value that cut the spikes down to something like acceptable. I would think 100μF would help a lot with a smaller Nextion than I was using. Any capacitor is better than none. Remember there are people out there using these things without capacitors and I guess they are not having problems, or they are having problems but they don't know why. If I'd not happened to be using a GPS receiver at the same time I probably would not have found out just how much electrical noise they generate.
I have a few of the small yellow capacitors with code 104 on I believe these are 0μ1 so I am ok for them thanks.
As a general rule always place them across the supply of any and all devices as close to the power pins as possible. If in doubt, use them. Within reason there is no such thing as too much capacitance across the power supply. Decoupling is a subject on its own though.
Am I also missing a trick as I am using two Easy Driver boards with a 19VDC input, each of them has a 5V output, should I be using this to power the screen/fan/arduino nano rather than add another supply?
See response from Koepel. No, in short. You need a buck converter. A regulator dumps excess voltage as heat, so 19V to 5V means 14/19 of the power going in ends up as heat and only 5/19 does anything useful. A switching converter swaps voltage for current; much less waste.
Get into the habit of collecting power supplies from old equipment that's being thrown away, that way you will always have a power supply for whatever you are making.
Thanks, I have a bag of old power supplies as you're right you never know, finding the 19V from an old HP laptop improved the stepper motors from the 12V supply I was originally using. Ideally I want to use that one supply for everything, 19V straight into the Easy Drivers with a buck supply (eventually) for everything that needs 5V; I have left an aperture in the box I printed for the Nano USB so I could change the sketch or update it if needed but I wanted to stick to one power lead in and a ribbon cable out to the steppers.
Thanks for the capacitor advice, it's a 3.5" screen so I will use the 100 rather than nothing. Everything worked ok when i connected it all on the breadboard but I have no idea what noise was present so better to put something in.