I just wanted to confirm something with you.
I have read many forum posts that discuss "how to power an Arduino with an External 5V power supply".
There are some comments that suggest to cut a USB cable and power the Arduino via the USB port.
There are other comments that suggest the 5V pin - and the dangers associated with this. Plus the possibility to use a Diode from the 5V to the VIN to protect against reverse voltage.... and I think I understand each of the suggestions from other posts on this forum.
I also read that you must supply the VIN pin with 7-12V - because the onboard 5V voltage regulator needs the input to be at least 2V higher for it to work.
I wanted to power the Arduino and the LEDs with that power supply at the same time, and so I connected the power supply to the VIN pin (and also to GND), and it worked ???
After all of the information that I read, I did not expect it to work, but it did.
So, is there any danger in powering the Arduino with 5V through the VIN pin ?
No danger.
If you feed 5volt into Vin, the Arduino will run on ~4volt (~1volt regulator dropout).
Undervolting is the same as overclocking.
It probably will work.
I would cut an old USB lead, and use that to supply the Arduino with 5volt.
But most people are not comfortable with that, and use the 5volt pin.
The advantage of USB supply is the onboard polyfuse.
Using the wrong USB wires cold harm your Arduino.!
Leo..
There is no actual danger, but I don't think it's a good idea at all. The VIN pin requires 7-12v if you supply power thereto. I understand it is essentially a power output point that is simply connected to the barrel jack to supply power to other shields. The most common of these is the Ethernet shield, which has its own on-board 5v regulators.
After all of the information that I read, I did not expect it to work, but it did.
I believe you were right to to expect it not to work, and it probably won't for long.
If you have a kosher 5v supply, you connect it to the 5v pin, or use a cut USB cable as you suggest..
There should be no damage to the hardware.
If the voltage is on the edge, and it drops a bit more, it may cause your process to reset, or stop working.
Have you checked that voltage with your volt meter? What does it really read?
If you do continue to use that setup, I would suggest some extra caps on the arduino power rails.
It's not a good idea because you intend to feed 5v into a terminal that requires a recommended minimum of 7v. Even if there is no actual regulation required, there will still be some losses and your Arduino will be running at about 4v. If it's just feeding the Uno and doesn't actually do anything more than keep the lights on, it will probably run but, as soon as you give it some work to do, it will probably give up. If you power all of your peripeirals directly with the 5v supply, the Uno may run for ever, but it's still a bad idea and not the sort of thing to to your mother about.
The voltage reading is 5.05V.
I have also used this setup for another similar project (but with less LEDs), and a different power supply (i.e Wall adapter - that has a voltage reading of 5.2V) - both work fine.
I have managed to do many LED animations using this setup, and have not come across any issues yet.. which is why I am asking this question, and wanted to make sure that there wasn't any damage that could be happening without my knowledge.... and then find one day that I have a burnt out Arduino.
You mentioned to use extra caps, and so now I am wondering whether my success with this circuit to date has been due to the 4700uF 16V Capacitor that I am using (as per the diagram in my original post). I had it there to protect the LEDs from any initial onrush of current from damaging the NeoPixels.
If the Arduino is running slower, then I would have thought that I would have problems with the LEDs, because they generally have specific timing requirements for them to work... but they seem to be doing exactly what I want them to do.
How many extra caps (and what size) would you suggest? And if you could - maybe explain the reason for your suggestion...
BTW... I am not ignoring the other suggestions to use an old USB cable, I am just trying to understand what exactly makes this particular working circuit a "bad solution".
Nick_Pyner:
It's not a good idea because you intend to feed 5v into a terminal that requires a recommended minimum of 7v.
I think you misunderstand. There is a Vin pin that needs a minimum of 7V and it goes through the regulator. But there is also a 5V pin that you can supply 5V to if you have a good clean regulated 5V source. That pin goes directly to the Vcc pin on the chip with no regulator or anything. That's the pin we're talking about. Minimum on it is 4.5V IIRC.
Whether or not feeding Arduino 5V through the 5V pin is good or bad depends entirely on the power supply. If it is a good regulated supply it could potentially be even better than the onboard regulator. If it is a noisy supply or the voltage sags on it then you may have problem.
It's not. It's still clocked at 16Mhz.
It might have trouble keeping up with that (fixed) speed.
Just plug the 5volt supply into the 5volt pin of the Arduino.
You don't seem to worry about all the processors inside the LEDs.
They also run on that 5volt supply, and fail if it gets over 6volt.
Leo..
Thankyou Delta_G & Wawa... yes I have read that using the 5V pin is an option.
Based on all of the comments so far, it appears that supplying the Arduino VIN pin with 5V will mean that the Arduino will be running off 4V - and this could cause problems because it may skip a few beats ... however it will not damage any of the hardware (based on the comments so far)...
So, if I am not experiencing any noticeable beat skips or lack of performance, then I could assume that there is actually nothing wrong with supplying the Arduino with 5V (with a 4700uF 16V Capacitor on the power rails)??
The recommended Voltage input to the VIN pin is 7V... and if my circuit did not work, then I would know WHY it is not working... because the required input needs to be 7V... but my circuit IS working with a 5V input, without any issues or problems, and is reproducible on a number of Arduino UNO boards that I have tried, and a couple of different 5V power supplies.
So if it works, and there are no performance issues, no damage, then I could assume it is safe to carry on with this set up?
Sorry - this is me trying to learn and understand "WHY it is working, and WHY it is not advisable" rather than HOW to do it differently....
The '328P will meet full spec at 16 MHz down to ~3.78V per Figure 29-1, Max Speed vs Vcc.
If you are using the ADC, voltages above Vcc + 0.5V will result in a reading of 1023.
Measure the VCC you are seeing and plan accordingly.
Vin goes through the onboard regulator.
Connect something else to the Arduino that draws power, and the regulator dropout voltage will increase.
You're probably now 0.22volt from the edge of the cliff.
Leo..
Excellent ! Thank you.. This is starting to make sense...
So the Voltage supplying the Arduino is 4V.... that means I only have ~0.22V up my sleeve.
I guess the signal line is not really drawing enough to kill the circuit
Does this mean that if I set a digital Pin to HIGH - that I will only get an output of 4V instead of 5V?
I am guessing that if I chose to use some sensors/INPUTS, that they may not work as expected?
Does this mean that if I set a digital Pin to HIGH - that I will only get an output of 4V instead of 5V?
Yes.
Any inputs should not exceed Vcc + 0.5V, and your high outputs will be no more than Vcc, and could be as low as ~Vcc - 0.8V with 20mA loads (higher for lighter loads).
ScottC:
Does this mean that if I set a digital Pin to HIGH - that I will only get an output of 4V instead of 5V?
I am guessing that if I chose to use some sensors/INPUTS, that they may not work as expected?
Excellent... ok this makes sense... and I can now see how this circuit could cause problems under certain circumstances.
Now... the alternatives.
Option1: old USB Cable
Option2: 5V pin (with a diode from 5V to VIN - to protect against reverse voltage)
I have a couple of different LED strips and 5V power supplies.
As mentioned previously, one has an output of 5.05V (Meanwell 5V 10A power supply), and a Plugpack adapter which has an output of 5.2V (PowerTran 5V 4A)...
I do not trust the PowerTran adapter as much as the MeanWell power supply, but it is much more compact and convenient...
a) What is the maximum voltage for that 5V pin ?
b) Is there any way to protect the Arduino ? Because this is now bypassing the onboard 5V regulator.
c) Does the USB cable option bypass the 5V regulator also ?
d) Which is the safest/best option (1 or 2)?
I guess there is another option (ie. Buy a 7V power supply)... but I am trying to avoid that
ScottC:
Option2: 5V pin (with a diode from 5V to VIN - to protect against reverse voltage)
The diode in question is NOT for Arduino reverse voltage protection, but for regulator protection.
Some people insist on using a diode there, but I don't bother.
If you power the Arduino from USB (= almost the same as the 5volt pin), you also haven't got that diode in circuit.
The only difference between USB 5volt and the 5volt pin is a polyfuse and a conducting mosfet (0.1ohm?).
ScottC:
a) What is the maximum voltage for that 5V pin ?
b) Is there any way to protect the Arduino ? Because this is now bypassing the onboard 5V regulator.
c) Does the USB cable option bypass the 5V regulator also ?
d) Which is the safest/best option (1 or 2)?
Max operating voltage is 5.5volt (absolute max might be slightly more). The RGB LEDs are 5.3volt max...
Make sure your supply is <=5.5volt.
Yes.
Meh.
Leo..
Thank you for your reply Wawa - that was very helpful.
How can I make sure that my supply stays below 5.5V (or 5.3V for the LEDs) ?
Do I need some extra parts?
I have read that zenner diodes can be used to clip the voltage to 5V... but not sure how that works, and whether they could handle the current requirements (of the LEDs).
