First time builder here. I’m trying to make an air quality sensor that detects PM2.5 concentration. I’d like to use the Arduino Nano, the air quality sensor SDS011, the Waveshare 1.54-inch E-Ink display, and a 5V fan.
A PDF of the nano’s pinout that I found states that each pin can support a max of 40 mA, recommended 20 mA, and that the total amperage should not exceed 200 mA. I’m still learning about electronics, so I don’t know how to be sure I don’t exceed that current draw, or how to ensure that all my parts are powered properly. My two questions are these:
How can I be sure that any given setup will not exceed a board’s maximum current rating (and, followup, how can I be sure that my specific setup will not exceed the nano’s maximum current rating)?
How should I choose a power supply for a board? Will any supply within a board’s specified range do, or are there cases where I should use a smaller or larger power supply (and, another followup, how should I choose a power supply for my specific setup)?
If weight is not an issue, and 120 VAC is available, I use nothing less than a Mean Well brand switching power supply. it's a quality thing; both physical quality and DC power quality.
do not power anything through the Arduino. it's a microcontroller, not a fuse. power the Arduino with the external power supply through a 5 volt pin.
After looking those up, the range of options is a little overwhelming, and I'm still not certain of which is appropriate for my project. Could you provide an example of which of their products you would use and what kind of project you might use it for?
...do not power anything through the Arduino. it's a microcontroller, not a fuse. power the Arduino with the external power supply through a 5 volt pin.
Noted, thank you. Should any power supply I use output 5V, then?
kronimiciad:
Noted, thank you. Should any power supply I use output 5V, then?
Yes, because that is the voltage the microcontroller requires.
Do not be deceived by the on-board regulator. It is basically useless, so ignore the "Vin" pin! You power the board via the "5V" pin and ground and you connect the same power supply to each of the other devices requiring 5 V.
The devices you have so far described require less than one Amp in total. I don't think you require a "Meanwell" caged power supply for this (though the laser sensor does specify a ripple tolerance - you may need to add a 1 mF - AKA 1000 µF capacitor across it).
USB "phone chargers" with a rating of either 1 or 2.1 Amps are readily and reasonably cheaply available. You just need to split out the connections from a USB "A" cord to get the 5 V output - generally red and black - for this.
aarg:
Please post the current consumption specification of all the devices you will use.
I'm not sure how to find that. That's why I've posted this question. I think that one term which may indicate how much current a part will pull is its rated amperage. In this case, the SDS011 is 70 +/- 20 mA, but I haven't been able to find anything about the e-ink display. There's a rated voltage, and it says that it can either be powered by 3.3 V or 5 V, but the spec sheet is in poorly translated English. Between the bad translation and a shallow understanding of technical language, I can't tell whether there's a tradeoff between supplying the display with 3.3 or 5 V. I think that section 3.4 of the spec sheet, titled "Power Consumption", indicates that the display will draw a max of 8 mA, but the unit they use is confusing (max 8 mAs, mAs=update average current×update time).
If that's so, and considering that the e-ink display will only draw power when it updates, would it be possible to run the display off the nano? Or should I connect it to a 5V supply along with everything else?
EDIT: Correction. I think that the e-ink display's store page says that the refresh power is typically 26.4 mW, so for 3.3 V that would be 8 mA, and for 5 V that would be 5.28 mA.
An appealingly quiet 5V fan I found has a power rating of 180 mW, so about 36 mA.
If I'm correct about what these terms mean, then I think my build would, at max usage, draw 134 mA of current.
Paul__B:
... (though the laser sensor does specify a ripple tolerance - you may need to add a 1 mF - AKA 1000 µF capacitor across it). ...
If I wired everything up without the capacitor, how would I know that it should have been added? Would the sensor not work, or would it just give inaccurate readings?
Paul__B:
USB "phone chargers" with a rating of either 1 or 2.1 Amps are readily and reasonably cheaply available. You just need to split out the connections from a USB "A" cord to get the 5 V output - generally red and black - for this.
So snip off the end of a USB A and wire it up to the 5V and ground pins of the nano, and connect the other components in parallel?
I looked up the laser sensor earlier. Its consumption is minimal and there is no point being concerned about 3.3 V or 5 V. I presumed this would be a small computer fan with similarly minor consumption. As I suggested, an inexpensive "phone charger" should be quite adequate. However using the much heavier Meanwell supply is perfectly appropriate and as suggested, you may well decide to add more stuff later.
kronimiciad:
If I wired everything up without the capacitor, how would I know that it should have been added? Would the sensor not work, or would it just give inaccurate readings?
It may give inaccurate readings.
kronimiciad:
So snip off the end of a USB A and wire it up to the 5V and ground pins of the nano, and connect the other components in parallel?
Paul__B:
...As I suggested, an inexpensive "phone charger" should be quite adequate. However using the much heavier Meanwell supply is perfectly appropriate and as suggested, you may well decide to add more stuff later. ...
At the moment, I'm trying to keep the project as strictly simplified as I can. I want to get my first project finished, because I have a habit of spending so much time planning and considering and experimenting that I never actually get started in earnest.
I'd wanted to be able to plug the build in to a small rechargable battery so that I could carry it just outside the house as well, so between that and trying to avoid mission creep a wall adapter with a USB plug may be the best option at the moment.
Also, I found a few 1 mF capacitors, but I notice that there's a lot of different kinds between rated voltages and materials they're made of. How should I choose? My guess is that higher rated voltages would draw higher currents when they're charging up, so it might be best to choose a rated voltage as close to 5V as possible.
EDIT: I've just found an old AC wall adapter from a phone I had several years ago. It's a Motorola Turbo Charger. The back reads
Could I use this for my power supply? My guess is that the supply will only output higher voltages when connected to a compatible device, but I also don't want to risk frying my board.
kronimiciad:
My guess is that higher rated voltages would draw higher currents when they're charging up, so it might be best to choose a rated voltage as close to 5V as possible.
And that guess is of course nonsense.
How much you need to charge a capacitor is entirely dependent on its capacitance. The voltage rating is merely a value that if you exceed significantly, you will hear a loud noise and experience a very bad smell. And you might get injured if you are close to the detonation.
The voltage rating is merely a value that if you exceed significantly, you will hear a loud noise and experience a very bad smell. And you might get injured if you are close to the detonation.
mushroom clouds and flying capacitor cans have been done. I was there, man.
Paul__B:
And that guess is of course nonsense. ...
Well, that's good to know .
Thank you folks for your help; I'll order a capacitor along with my other parts.
Does anyone know whether that turbo charger wall adapter will work? Getting a new adapter wouldn't be too expensive, but it'd be nice to not need one. I tried checking with Motorola tech support to be sure that it would only put out more than 5 V if connected to a Motorola device, but they couldn't help. Maybe a phone supply store would know
