Air Sensor box with UNO - Beginner power question

Other Hardware General Electronics
1

Hi there! thanks for reading so far already :slight_smile:

I'm building a air sensor box with the UNO rev3 and several sensors.

  • Winsen MH-Z19B CO2 Sensor ( +/- 150mA peak)
  • DHT22 temp hum sensor (2.5mA)
  • Seeed grove HCHO gas sensor (can't find any current information, Operating Voltage: 5.0V ± 0.3V)
  • 5 neopixels (5x max 60mA = max 300mA)
  • LCD crystal 16x2 display (the standard in the Uno starter kit) , 24mA (if Iremember right
  • Nova SDS011 High Precision Laser Dust Sensor (80 mA peak)
  • Uno itself about 50mA

So total would something like +/- 560 mA for all the components. So 1A supply would be enough.

I started the project with LCD + DHT22 + Co2 sensor (max 175mAh), where the LCD starts flickering when CO2 sensor takes a measurement. The circuit is powered via the 5v pin and the UNO is powered via the USB port.
When I use a 12v 1A power adapter, the lcd is steady.

Some things I don't understand, and like to know:

  1. USB power should be 500mAh, plenty for the current setup (LCD + DHT22 + Co2 ), so why is it unstable (flickering LCD)?

  2. I read a lot on this forum it's better to power the Uno and components seperately, and that the max power via/from the Uno (5v pin) should max 150-200 mA. While the document says it can be 1A. Also powering via the barrel or Vin seems to be not advised for long term setups, because of overheating. But why was is design like this, only for prototyping?

  3. I like to have 1 power supply of 5v and 1A, I already have a adapter I can use.
    If the USB port is the best and most secure way to power the board, how do I also power the circuit? (as Vin is 7-12v and also not the recommended way).
    I read a lot here about buck converters to make 5v stable or to convert 7-12v to 5v, wondering it would be a way to use the 12v adapter, split the supply in 12v for the arduino Vin (which still doesn't seem the best way) and a buck converter to power the components with 5v.
    What's the best and most safe way to power my project?

Am I thinking too complicated? It feels too complicated for the purpose of arduino and easy te learn design.

Sorry, the story became too big. Thanks for reading anyway.

2

To power the Arduino from a 5V supply, connect it to the "5V" pin, not the USB port.

If the Arduino is powered by USB or Vin, you should not use the 5V pin to provide power to motors, servos or gas sensors with heaters, as that can damage the on board regulator (or the USB port).

3

That's strange. When I look up the device, I see the internal heater requires 100mA. So you are exceeding the current rating of your power supply, as indicated by the results you see.

When in doubt about the current requirement, measure the actual current while your project is running.

4

Thank you for your quick answer jremington!
But I also read here on the forums (and the docs) that the 5V pin is not recommended because it's less secure / not regulated. So is there better alternative or did I misunderstood?

5

Thanks for looking up Paul! I couldn't find it in the sheets but was looking at the wrong place maybe.