While you can power the Uno with 12V into the barrel jack, the on-board regulator has to drop that to 5V. This regulator is not heat-sinked. You can run it this way for a few hours (I have) but if you plan to have this running 24/7 then the Arduino should have its own 5V supply.
the other branch will go into the Arduino using the barrel jack.
What you are saying is if my Arduino will be plugged 24/7 ( that's the case) i need to put a voltage divider on the branch going to the Arduino to drop the voltage to 5V, that way i will not have any issue ?
Not a "voltage divider"; a switchmode "buck" converter feeding the 5 V into the "5V" pin on the Arduino and any other device requiring 5 V.
thank you, but as i said in my first message, with the ongoing crisis, i'm not able to buy any other equipment that i already have. I dont have any buck converter and i've look and i think i dont have all the component to made one by myself.Why cant i use a voltage divider, is that not its purpose to drop voltage ? can i use a potientometer ?And why the arduino can take up to 12V if there is not heat sink that can support it when it dropped voltage to 5V ?
A resistor voltage divider is also a current limiter. It's good for high-impedance inputs, but not for a power supply.Why are you not able to buy a bucking voltage converter? Amazon.com doesn't work where you live?But to your last question.Arduino was designed as an educational tool and expected to be used for brief periods, say a classroom. The voltage regulator was included to give the new user a lot of flexibility to power the board. Most development kits come with a 9V battery to plug into the barrel connector.How brief? I don't know. I have a project that is powered by a 12-V wall-wart into the barrel jack of an Uno that has run for a few hours without a problem.
I understand for the voltage divider thx about the other subject, the arduino uno faq page said:'' The board can operate on an external supply from 6 to 20 volts. If supplied with less than 7V, however, the 5V pin may supply less than five volts and the board may become unstable. If using more than 12V, the voltage regulator may overheat and damage the board. The recommended range is 7 to 12 volts. ''so why can i put into it 5V? the board will not be unstable ? How many hours is ''few hours ? I may need to power it 3-4 hours in the morning after what it will not run till 5PM for 2 hours for every day. Is that too much for the arduino on the long term ?thank you
The stepper motor will use an h-bridge (IC driver L293D) controlled by the arduino
An Uno with no external loads should draw approximately 100mA from the 5 volt supply. As mentioned, you should be able to power the Uno from 12 volts into the barrel jack without difficulties if and only if the 5v supply has no additional loads on the 5 and 3.3 volt outputs. How do you know if 12 volts input is okay? Simple. So long as the large three terminal 5 volt regulator between the usb and barrel jacks is only warm to the touch, everything is fine, carry on. If it gets too hot to touch (>45-50C), you'll need to reduce the 12 volts going into the barrel jack to lower the power being dissipated by the 5 volt regulator. One method that doesn't involve buying a buck regulator is to place about six 1N400x series diodes in series with the supply - as each diode will drop the voltage by approximately 0.6 to 0.7 volts each. 7.5 to 8 volts input to the barrel jack is the ideal voltage for the regulator. If you have an Uno clone, there may be two regulators, a 5 volt and a 3.3. They both should only be warm to the touch, too hot to hold your finger on it requires a fix of some kind.
Another terrible idea.First of all the L298 and family should be retired, there are far better H-bridges out there nowadays. It's from a bygone era, when a 3-4V loss on your H-bridge was simply part of the game and considered normal. Not any more, modern H-bridges do more current in a smaller package without the need of a heat sink. Then the resulting 8-9V your stepper sees may be way too much for it: steppers are supposed to be current driven, not voltage driven.Secondly, a stepper runs much better (easier control, smoother running, higher torque at speed) with a proper stepper driver. Lots of different drivers out there, A4988 comes to mind as a cheap one that will handle a 350 mA stepper just fine. The stepper driver will make sure the stepper gets the current it needs, regardless of input voltage - in fact higher supply voltage is better (subject to the driver's limit).
i may need help about the wiring though. Do i need a common ground for everything? i mean i split the vcc of the wall-wart and put one branch into the L293D pin 8 the other one goes to the barrel jack but what about the ground? do i cut it or the ground only goes to the barrel jack and everything will be fine ?
Check your stepper's specifications as the voltage it gets may simply burn it for giving it too much current.