I am loving tinkering with my arduino Nano and learning as I go along from my mistakes, but I have come up against something I cannot understand.
I am using a Nano with temp sensor and relay to power a 12v fan for my greenhouse. I have connected all the parts and written the code, and connected a bluetooth module so I can read temp from my phone from outside the greenhouse.
When I have been constructing it and writing the code, the Nano has been connected via usb to my pc, and all works fine. However, when I connect the Nano to a brand new, fully charged 12v 44ah car battery, again everything seems to work fine, except the bluetooth module - which flashes the red LED a few times, then goes off and the phone can't detect it. (I have 3 B/T modules and tried them all)
I have put a meter across the gnd and 5v of the Nano when plugged into the usb and get a steady 4.43v.
When I do the same while connected to the battery, it starts at 4.98, but quickly drops to 3.83 and then fluctuates between 3.83 and 4.10v, which it would seem is below the operating voltage of the bluetooth. At this point the sensor and relay LED are not a constant brightness, but dimming and brightening.
At the Nano GND and VIN, I am still reading 12.9v.
When connected to the battery the 5V is supplied by the on board 5V regulator. The maximum recommended dissipation of the regulator is 1 Watt. So the maximum current is 1W / (12V - 5V) = 143mA. 50 to 60mA of that is used by the Nano. So if the peripherals draw much current, the regulator output can drop. I would suggest that you feed a DC-DC 12-5V converter (buck) with the 12V battery and connect the 5V output to the Nano 5V, bypassing the weak 5V on board regulator.
Your Bluetooth module is pulling too much current from the Arduino's 5V regulator. (When you power via USB you are bypassing the on-board regulator.)
Measure the total current from the battery and then I recommend getting a switching 12-to-5V DC-DC converter with enough current capability to to power the Nano and the Bluetooth module (again bypassing the on-board regulator).
A switching converter/regulator is more efficient than the on-board linear regulator. You'll be pulling less current on the 12V side (for longer battery life) with the same current on the 5V side. Although, the battery life is probably mostly-determined by the fan's power consumption.
The Comparator U5A OUTPUT goes HIGH if Vin Voltage >6.6V because RN1A & RN1B are the same value,
so the threshold trip point is 2x U5A V- input (3.3V).
This means as soon as you apply power >6.6V to Vin, mosfet switch T1 turns OFF, killing USB input power
by switching off that input. If the bluetooth is connected to the Nano 5V, it will draw too much current from
the onboard regulator which is already dissipating 12V-5V = 7V @ ILoad |Where ILoad = 50 to 60mA for the Nano plus whatever the Bluetooth draws , so , for example, if
ILoad = 0.2A, *7V (12-5) = 1.4 Watts. The NCP1117ST50T3G 5V regulator is rated for 1.0 A @5V , but that's without
the 7V excess input voltage. It's probably overheating and that derates the output voltage, or the Bluetooth is just overloading it.
You have things a little mixed up rschammel. Your discussion refers to the Uno.
Nano uses a MBR0520 diode to prevent regulator voltage from backdriving the USB source. If there is no input power from regulator, USB power is used. If there is input power and the voltage is higher than USB, than US power is blocked by the diode.
TIMC1, you are probably seeing the regulator overheating shutting down, restarting etc.[/ltr]
If you are using the 3.3V supply, that is provided by the FTDI chip and is only capable of 50mA.
The UA78M05 regulator can support a couple hundred mA, but the datasheet only shows results with Vin @ 10V.
Your suggestion to look for a 12V to 5V stepdown regulator is a good one.
A very real danger is that the obsolete tutorials on the Arduino site and others misleadingly imply that the largely ornamental "barrel jack" and "Vin" connections to the on-board regulator allow a usable source of 5 V power. This is absolutely not the case. It is essentially only for demonstration use of the bare board back in the very beginning of the Arduino project when "9V" transformer-rectifier-capacitor power packs were common and this was a practical way to power a lone Arduino board for initial demonstration purposes. And even then it was limited because an unloaded 9 V transformer-rectifier-capacitor supply would generally provide over 12 V which the regulator could barely handle.
If you are asking this question, it is highly likely that you will wish to connect something else. In which case, the answer is regulated 5 V.
This is because the on-board regulator is essentially capable of powering only the microcontroller itself and no more than a couple of indicator LEDs. The on-board regulator might be able to power a few other things if it had a heatsink, but on the (older) Arduinos, it does not.
Powering via the "barrel jack" (on a UNO) or "Vin" connections is asking for trouble. The "5V" pin is not by any means an output pin, if anything a "reference" pin but most certainly the preferred pin to which to supply a regulated 5 V.
For use in a car, a switchmode "buck" regulator is the way to go.
I originally used a USB but switched to using
9V dc wall warts in the barrel jack and have
done that for at least 5 or more years and never
had any problems. When I need several breakout
boards I use OKI 5V switching regulators or
5V dc wall warts. Never had any issues using
the barreljack. I've always liked the convenience
of a jack for the Wall wart dc input.
Paul__B:
A very real danger is that the obsolete tutorials on the Arduino site and others misleadingly imply that the largely ornamental "barrel jack" ....
Why are you always railing against the barrel jack? Compared to supplying power through a pair of Dupont connectors, the barrel connector is far, far more robust.
As long as you stay within the specs, you should not have a problem. I have a couple of projects that are an Uno powered with a 12V wall wart through the barrel connector, and a Wemos D1 mini getting its power from the +5V pin on the Uno. They have been running since January and the reglator chip on the Uno is not even warm to the touch.
Because people frequently if not usually want to connect other things.
Now why you would use an Arduino UNO and a WeMOS D1 mini together, that is a puzzle!
You are depending on the WiFi only intermittently drawing power.
My project is a telephone for an escape room. The Arduino handles the Adafruit Wav Shield which supplies audio to the handset. All of the dialing, hook switch, ringer and WiFi logic is done in the Wemos D1. The Wemos tells the Arduino using wire.h which audio file to play.
