Arduino Forum

Using Arduino => Displays => Topic started by: avalon66 on Apr 17, 2019, 11:35 am

Title: MAX7219 problem
Post by: avalon66 on Apr 17, 2019, 11:35 am
I bought a MAX7219 last week and together with a DS1307, I put a project together to give scrolling text.
the MAX7219 will light up, but go off with a usb cable connected, and does the same with a 5v 2.5 amp power supply.

Is the display faulty, and if so where can I get a decent quality one from in the UK.

Thanks
Title: Re: MAX7219 problem
Post by: Paul__B on Apr 17, 2019, 12:13 pm
Are you kidding?  :smiley-roll:
Title: Re: MAX7219 problem
Post by: avalon66 on Apr 17, 2019, 12:32 pm
Are you kidding?  :smiley-roll:
Nope, I'm not, and have tried different jumper wires, crimping the female end onto the pins of the MAX7219, 2 different arduinos and 2 different pcs.
The result is always the same, lights up then goes off. It is the only thing connected to the arduino and won't display a simple 'hello' sketch.
Title: Re: MAX7219 problem
Post by: PerryBebbington on Apr 17, 2019, 01:20 pm
You are asking us to help you without seeing your circuit diagram or your code. There are some very clever people on here but I don't think any of them are mind readers. I would have thought that with 152 posts you would know by now the requirements listed in 'how to use this forum - please read'.
Title: Re: MAX7219 problem
Post by: avalon66 on Apr 17, 2019, 02:04 pm
Basically I was just asking for a more reliable MD7319 display, and that's why no code nor circuit diagram.

Anyway here they are now

Update:

The display finally displayed an 'hello' sketch, so I then uploaded the sketch , which I have attached. Tyhe display sowed some of the text as 1 of the modules of the 4 was still lit up red. I tried it again , a few times , and once or twice it did display the text on all 4 modules.
But now , with a usb lead plugged in the display is flickering..

Title: Re: MAX7219 problem
Post by: PerryBebbington on Apr 17, 2019, 03:30 pm

Quote
Anyway here they are now
Well, sort of. Have you actually read 'how to use this form, please read', or just forgotten what it says?

Title: Re: MAX7219 problem
Post by: avalon66 on Apr 17, 2019, 05:42 pm
Yes I have read 'how to use this forum', and njo I had notvvforgotten what it says.

First I spent hours googling the problem, but nothing came back relating to my problem of going off as soon as it goes on, worked once but not since, and now flickering.

Some times just a mere touch of any wire brings it back to life, but not for long tho'
The code I uploaded is too big , over 600 lines, to post in code tags as I tried it.

One thing I have noticed is that the voltage to the display varies more or less each time it is plugged in to a usb cable, from 2.6v upto 3.8v. Now considering it is a 5v device, the low volatge readings could have something to do with it.
Title: Re: MAX7219 problem
Post by: marco_c on Apr 17, 2019, 11:52 pm
Your wiring is probably faulty.

Check if the display BY ITSELF runs properly with the standard MD_Parola examples
If it does not, then ensure your ground and power wires are well connected. Change the location on the breadboard if needed to make sure this all works.
If it does, then try running your clock on its own with the example from that library, etc.

Basically adopt a structured approach to finding your issue.
Title: Re: MAX7219 problem
Post by: BJHenry on Apr 18, 2019, 12:16 am
As I said in one of your previous threads on this topic, you can't power a display that size from the 5V pin of the Arduino. You should disconnect the 5V wire from the display and connect it straight to an external 5V supply, and then connect the ground of that external supply to the ground of your Arduino or display. The Arduino ground still needs to be connected to the display ground. For the description you've given previously it sounds like you might have been connecting the external supply to the Arduino rather than the display, this isn't the case. You also ran power to the display via a solderless breadboard using a piece of breadboard wire. Don't do this, use a proper piece of wire going straight to the display.
In your other thread you mentioned that the supply voltage was sagging when you were trying to use the display. That shows that there is an issue with the supply so unless you've sorted that out then I'm not surprised that you're still having issues.
Title: Re: MAX7219 problem
Post by: avalon66 on Apr 18, 2019, 12:43 pm
This how I read what you say:

I connected the 5v wire from the display to vcc on a female barrel connector.
The ground from the barrel connector went straight to Arduino gnd.
A gnd from the Arduino goes to the gnd on the display.

The 5v wire from the Arduino to vcc on the breadboard, to power the other devices

All I got was just 1 vertical line of leds lit up on the display at one end. The next time I tried it , there was no lights lit up.

I've either misunderstood you and / or have got something wrong.

I found a 9volt power supply which powers all the devices as well as the dispaly. On checking the voltage to each device I got 4.8 volts + / -

Thanks
Title: Re: MAX7219 problem
Post by: BJHenry on Apr 18, 2019, 02:56 pm
Something isn't adding up there. If you are supplying 9V straight to the display then the voltage at the display should 9V, not 4.8V. It sounds like you either aren't connecting everything the way you describe, you aren't measuring correctly, or there is a short in your wiring that is dragging the supply voltage down. 4.8V is suspiciously close to 5V though.
Can you show us a clear photo of your wiring?
Title: Re: MAX7219 problem
Post by: avalon66 on Apr 18, 2019, 03:38 pm
A picture of the wiring, and hope it is clear enoufgh.

Take no notice of the DHT densor being the wrong round in the photo, it was correcred  after I took the picture, and it working ok now
Title: Re: MAX7219 problem
Post by: BJHenry on Apr 19, 2019, 06:04 am
OP's picture:
(http://forum.arduino.cc/index.php?action=dlattach;topic=610613.0;attach=304467)
Thanks for sharing that.
I don't see any external power supply there. Maybe I'm missing something?
Title: Re: MAX7219 problem
Post by: Paul__B on Apr 19, 2019, 07:12 am
I don't see any external power supply there. Maybe I'm missing something?
Let me re-phrase that.

I don't see any power supply.  So we are none the wiser as to however he is/ was powering it.  :smiley-eek:

Having it on its side does not help either.  :smiley-roll:  Even though it would be the same picture (and comes up the right way if I "view image",) somehow that makes it more difficult to figure out.



How does that happen?  I think he was using the camera on its side and its gravity sensor Exif information is handled differently by different viewers.  :smiley-eek:
Title: Re: MAX7219 problem
Post by: avalon66 on Apr 19, 2019, 10:46 am
Sorry about that, but the reason for no power supply is because the picture was taken outside for better lighting.This was pointed out to me on this site sometime ago now. i.e
Take pictures outside so it is easier to see the parts and wiring.

The picture now shows the power supply plugged at the top right corner, and I have tried to use as many different coloured wires as I could.
Title: Re: MAX7219 problem
Post by: BJHenry on Apr 19, 2019, 02:58 pm
Ok, it is like I thought. That external power supply is connected to the Arduino's onboard regulator, NOT directly to the display like has been suggested several times.
What's happening with your setup there is that the external supply is powering the voltage regulator on the Arduino board which is then trying to supply the display and all the attached devices. The limiting factor there is the Arduino's onboard regulator, which isn't able to supply enough current no matter what size external regulator you plug into it.
What you need to do is disconnect the 5V wire from the display and connect it directly to an external 5V supply. You will still need to connect the ground from the external supply to the Arduino ground.
Title: Re: MAX7219 problem
Post by: Paul__B on Apr 19, 2019, 03:20 pm
Sorry about that, but the reason for no power supply is because the picture was taken outside for better lighting.This was pointed out to me on this site sometime ago now. i.e
Take pictures outside so it is easier to see the parts and wiring.
OK, that would indeed have been my advice on the forum.

(https://forum.arduino.cc/index.php?action=dlattach;topic=610613.0;attach=304557) (https://forum.arduino.cc/index.php?action=dlattach;topic=610613.0;attach=304557)


You clearly would not have wanted to connect a 9 V power supply to the 5 V rail - that would be catastrophic.

Unfortunately, there is a common misunderstanding that the on-board regulator on the UNO/ Nano/ Pro Mini/ Leonardo is actually useful for anything.  It is not.  It is essentially an ornament provided in the very beginning of the Arduino project when "9V" 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.

Nowadays, 5 V regulated switchmode packs are arguably the most readily available in the form of "Phone chargers" and switchmode "buck" regulators are cheap on eBay so these can be fed into the USB connector or 5 V pin to provide adequate power for most applications.  Unfortunately, many tutorials or "instructables" are seriously outdated or misleading and have not been updated to reflect the contemporary situation.

Title: Re: MAX7219 problem
Post by: avalon66 on Apr 20, 2019, 10:39 am
It was sometime last year, that I asked about what power supply I could use for 12v led strip and arduino, and was told anything between 7v and 9v to the arduino.

As I said earlier in this thread, the voltage to the board and devices is 4.92v. As BJHenry said that something is dragging down the voltage, which I suspected when just using a 5v powersupply, which wouldn't power the display and show anything.

I did try to power this project with 9v to the breadboard, but the display screen came on then went off again.

How should I power the whole project, so that everything works

From  this link:

https://arduino.stackexchange.com/questions/4458/what-are-the-5v-and-vin-pins-for

I read this: from the Arduino website:
5V. This pin outputs a regulated 5V from the regulator on the board. The board can be supplied with power either from the DC power jack (7 - 12V), the USB connector (5V), or the VIN pin of the board (7-12V). Supplying voltage via the 5V or 3.3V pins bypasses the regulator, and can damage your board. We don't advise it.

Then someone posted this:
Yet, provided that you do not exceed 5.5 volts on the +5v pin, you can absolutely use it to supply the arduino. You bear the responsibility of ensuring that you do not exceed 6v though. - David Hoelzer
Title: Re: MAX7219 problem
Post by: BJHenry on Apr 20, 2019, 02:33 pm
This is correct:
I read this: from the Arduino website:
5V. This pin outputs a regulated 5V from the regulator on the board. The board can be supplied with power either from the DC power jack (7 - 12V), the USB connector (5V), or the VIN pin of the board (7-12V). Supplying voltage via the 5V or 3.3V pins bypasses the regulator, and can damage your board. We don't advise it.
with the added caveat that the amount of current that the regulator on the board can supply is fairly low. It cannot supply enough current to run your LED display.

How should I power the whole project, so that everything works
What you need to do is disconnect the 5V wire from the display and connect it directly to an external 5V supply. You will still need to connect the ground from the external supply to the Arduino ground.
Title: Re: MAX7219 problem
Post by: Paul__B on Apr 20, 2019, 05:20 pm
Supplying voltage via the 5V or 3.3V pins bypasses the regulator, and can damage your board. We don't advise it.
The first part of this statement is total nonsense.  Now there is never any need to supply 3.3 V to the UNO or Nano because the only device which uses 3.3 V is the USB to serial chip and that always generates its own 3.3 V which is what also comes out to the 3.3 V pin, so not feeding power into that pin is a given.

Supplying 5 V to the "5V" pin certainly does bypass the regulator which is exactly what you want to do as the regulator is essentially useless.  Supplying 5 V to the USB port also bypass the regulator, which makes that part of the statement complete drivel.  Unfortunately, we cannot edit that absurd statement on the Arduino website.

Incidental - there is a concern that powering via the 5 V pin while the USB port is connected to a PC or laptop may "back-feed" the USB port and damage the computer and not the Arduino, but since the majority of powered USB hubs also do precisely that, the risk would seem to be fairly low.

So given your display will require no more than half an Amp, you can feed 5 V from a "Phone charger" into the USB port and take it from the "5V" pin to the display.  If you had a display requiring significantly more than half an Amp, you would connect the 5 V power directly to the display and the "5V" pin as well.
Title: Re: MAX7219 problem
Post by: avalon66 on Apr 20, 2019, 07:36 pm
What you need to do is disconnect the 5V wire from the display and connect it directly to an external 5V supply. You will still need to connect the ground from the external supply to the Arduino ground.
As last time I tried it, the display does not come on

I found this bit of information:

The barrel connector can be supplied an input of 7-12V. This is regulated to 5V by the onboard voltage regulator, and the board is powered on.

On here:
https://www.technobyte.org/2016/07/power-up-the-arduino-uno/
Title: Re: MAX7219 problem
Post by: Paul__B on Apr 21, 2019, 12:45 am
I found this bit of information:
The barrel connector can be supplied an input of 7-12V. This is regulated to 5V by the onboard voltage regulator, and the board is powered on.
Yes indeed, you found that "bit of information", but it is totally useless.  It is only relevant to powering the UNO itself with no other components connected apart from half a dozen LEDs limited to 20 mA each with the appropriate resistors.

That is not what you are doing here, so that "information" - such as it is - is not relevant.  Please forget it and stop dredging for nonsensical help elsewhere.  :smiley-eek:

You need a proper 5 V, regulated, power supply and I have described the options for connecting it.  I think you have been confused by BJHenry's quote that you cite suggesting that you "disconnect the 5V wire from the display" and are doing something peculiar.  Please describe - with pictures would be good - exactly what it is you have for a 5 V power supply and what connector it has.
Title: Re: MAX7219 problem
Post by: avalon66 on Apr 21, 2019, 10:32 am
Thanks, and the reason I went googling for information , as I usually do before I post on here , is because I was asked if I had done that when I post questions in a particular section of the forum.

The attached picture shows the whole project and the parts/devices which need 5v.

The 5v power supply I have is an AC/DC Adaptor, MYVOLTS,  model number DD132MU with a barrel connector. I don't know if there is any standard for barrel connectors , but I assume it is standard.

When you say " feed 5 V from a "Phone charger" into the USB port ", I can't do that because the usb type on my phone chargers are all different than the USB type on the arduino. It is what I would call, a 'printer cable' or socket

Thanks

Title: Re: MAX7219 problem
Post by: Paul__B on Apr 21, 2019, 12:36 pm
(https://forum.arduino.cc/index.php?action=dlattach;topic=610613.0;attach=304843) (https://forum.arduino.cc/index.php?action=dlattach;topic=610613.0;attach=304843)


Unfortunately, the "MyVolts Website (https://myvolts.co.uk/)" repudiates the model number DD132MU, so that does not help.

Nevertheless, it is useless plugging it into the "barrel jack" on the "UNO" just because you have a power supply with a barrel connector and a UNO with a barrel jack.  This is not how electronics automatically works, maybe just OK for garden  watering.  :smiley-roll:

If it is a 5 V regulated supply, you need an adapter to connect it to your 5 V wiring.
(https://i.ebayimg.com/images/g/cVkAAOSw6EZbozYN/s-l1600.jpg) (https://www.ebay.com/itm/5x-DC-Power-Adapter-5-5-2-1mm-Female-Socket-to-Screw-Terminal-Block-Adapter/223444782596)


If using a "Phone charger", you would want one with a USB socket on the charger (no shortage of those) so you can connect a USB "A" to "B" printer cable.  I pick these up at "garage sales", so they are not hard to come by.
Title: Re: MAX7219 problem
Post by: avalon66 on Apr 21, 2019, 01:31 pm
When I tried the 5v wire from the display to the 5v side of the power supply, I used one of thos female barrel connectors with a vcc and gnd wire attached the it. The 5v wire  from the diplay was connected  to the 5v side of the connector.

Googling 5v regulated power supplies :

This type:
https://uk.rs-online.com/web/p/ac-dc-adapters/4237931/ (https://uk.rs-online.com/web/p/ac-dc-adapters/4237931/)

Then this type:

https://uk.rs-online.com/web/p/embedded-switch-mode-power-supplies-smps/6802748/?relevancy-data=636F3D3126696E3D4931384E525353746F636B4E756D626572266C753D656E266D6D3D6D61746368616C6C26706D3D5E2828282872737C5253295B205D3F293F285C647B337D5B5C2D5C735D3F5C647B332C347D5B705061415D3F29297C283235285C647B387D7C5C647B317D5C2D5C647B377D2929292426706F3D3126736E3D592673723D2673743D52535F53544F434B5F4E554D4245522677633D4E4F4E45267573743D36383032373438267374613D3638303237343826&searchHistory=%7B%22enabled%22%3Atrue%7D (https://uk.rs-online.com/web/p/embedded-switch-mode-power-supplies-smps/6802748/?relevancy-data=636F3D3126696E3D4931384E525353746F636B4E756D626572266C753D656E266D6D3D6D61746368616C6C26706D3D5E2828282872737C5253295B205D3F293F285C647B337D5B5C2D5C735D3F5C647B332C347D5B705061415D3F29297C283235285C647B387D7C5C647B317D5C2D5C647B377D2929292426706F3D3126736E3D592673723D2673743D52535F53544F434B5F4E554D4245522677633D4E4F4E45267573743D36383032373438267374613D3638303237343826&searchHistory=%7B%22enabled%22%3Atrue%7D)


I would prefer the barrel type on , because of size and space, and as the prioject will be in a place wher it would be seen by other people, then it has to look neat and tydy.
Title: Re: MAX7219 problem
Post by: Paul__B on Apr 21, 2019, 02:43 pm
Well, of those two power supplies, the second is mad overkill - as is the link to it in which you omitted to remove the "?" and all the garbage following, so the proper link is actually https://uk.rs-online.com/web/p/embedded-switch-mode-power-supplies-smps/6802748 (https://uk.rs-online.com/web/p/embedded-switch-mode-power-supplies-smps/6802748).

I do not like the first for two reasons - it is a "linear regulated" supply so it is bulky, heavy and runs hot which means the capacitors tend to dry out after a few years at which point it starts to generate pulsatile DC and makes you wonder why your system fails to work with the most peculiar of symptoms.  A switchmode supply generally runs cooler so despite having more capacitors and components, it is likely to be more reliable (as they generally are in PCs).

The second problem is as pictured, it is supplied not with a fixed "barrel" connector, but a two pin socket and a barrel adapter so that you can use it if you wish with a rogue appliance which uses a centre negative connection.  This results in a substantial risk that at some stage unless you are very effective in gluing the adapter to that two pin connector, someone will accidentally pull it apart and reconnect it the wrong way round.

Now for that very reason, the "barrel jack" input on the UNO has a polarity protection diode - which wastes 0.65 of a Volt and prevents such mishaps.  As I explained before, this was very appropriate for using the UNO as a concept demonstration toy, but not useful for serious applications.  Feeding 5 V directly to the board - the correct way to do it - relies on the guarantee that there is simply no possible way that it will be connected in reverse.  If I encounter such power supplies with  polarity adaptors, I generally cut off the connector and either solder the wires directly to what I need to power, or solder on a proper connector to match the device.

But that's just how I do things.  Behind me is a mini-laptop (can't get them anymore - the usual word was "netbook") which used a quite tiny "barrel" connector which in turn eventually failed mechanically as you would expect.  So I drilled a hole next to the jack, cut the connector off the cable and soldered the adaptor wire directly to the PCB.  No power problems at all after that - but the battery and subsequently the screen failed.
Title: Re: MAX7219 problem
Post by: avalon66 on Apr 21, 2019, 05:10 pm
I linked the 2 power supplies just as example of type, not that I would buy the first one anyway. the second one, I do have, and it is in use.

Regarding the link for the 2nd one, I didn't know anything about removing the ?.

How or what way should I power everything with a 5v power supply, Buy a proper regulated power supply and connect it to a barrel jack, then 5v wire direct to the display and gnd to the arduino.??

As  I'm not an EE, my foray into this world is purely amatuer, and no doubt it shows!

I have tried a printer usb cable from a multi adaptor charger and it lit up the display , then went off.



Title: Re: MAX7219 problem
Post by: Paul__B on Apr 22, 2019, 02:00 am
Regarding the link for the 2nd one, I didn't know anything about removing the ?.
That absolutely ridiculous "tail" string on eBay or Aliexpress or RS is a tracking code for while you were browsing.  No-one else wants it and indeed, you do not want it either!

How or what way should I power everything with a 5v power supply, Buy a proper regulated power supply and connect it to a barrel jack, then 5v wire direct to the display and gnd to the Arduino.??
Well, the "barrel" jack is a very practical way to plug in a power supply so it is removable when needed.  The 5 V supply with a fixed line connector of the correct polarity would be appropriate, and your box can have the corresponding jack fitted.
(https://i.ebayimg.com/images/g/HXgAAMXQKq5R502z/s-l1600.jpg) (https://www.ebay.com/itm/New-5-5-mm-x-2-1mm-DC-Power-Jack-Socket-Female-Panel-Mount-Connector/372642952320)

I have tried a printer USB cable from a multi adaptor charger and it lit up the display , then went off.
So we want to know the voltages when it did so - and what "multi adaptor charger" it was.
Title: Re: MAX7219 problem
Post by: avalon66 on Apr 22, 2019, 10:37 am
The multi adaptor charger is a:
iSmart+ RAVPower, model: RP-PC020, input AC 100-240V 50/60Hz0.8A Max. Output is DC 5V/6A Total (Each 2.4A Max).
There are 3 usb ports on it

Voltages when using a USB lead from the muti charger:

Breadboard 5.03v
RTC 4.92v
DHT 3.1v
Display 3.1v

Title: Re: MAX7219 problem
Post by: Paul__B on Apr 22, 2019, 11:41 am
So you are saying there is a missing connection somewhere between the breadboard and display?

You last posted this "diagram":
(https://forum.arduino.cc/index.php?action=dlattach;topic=610613.0;attach=304843) (https://forum.arduino.cc/index.php?action=dlattach;topic=610613.0;attach=304843)


Let's see.  Is this still your assembly?  And your power supply is plugged into the USB port?

(https://forum.arduino.cc/index.php?action=dlattach;topic=610613.0;attach=304557) (https://forum.arduino.cc/index.php?action=dlattach;topic=610613.0;attach=304557)


So where on this are these voltages?  When you say it worked and then "went off", did the Arduino pilot light dim?
Title: Re: MAX7219 problem
Post by: avalon66 on Apr 22, 2019, 12:16 pm
The only difference now witrh the assembly is that the whole project is in a wooden box, and the display sits in a slot on one side of the box, and the DHT sensor is on extension wires so that it would be outside the box for more accurate reading.

When using the usb lead from multi adaptor the display lights up immediately, then goes off. The Arduino on led does not dim at all, and the voltage across the vcc and gnd of the display is 3.1v nominally.

No, I am not saying that there is a missing connection at all, and the connections are still the same as on the first picture.
Title: Re: MAX7219 problem
Post by: Paul__B on Apr 22, 2019, 04:37 pm
Well, 5 V is going into the USB jack on the Arduino.  Apparently 5 V is coming out of the Arduino "5V" pin and going to the breadboard.  The same 5 V is now supposed to be going to the display module but you are measuring only 3.1 V at this point.  So where is the break in the circuit?
Title: Re: MAX7219 problem
Post by: avalon66 on Apr 22, 2019, 04:47 pm
I'm confused somewhat, because if the project works with 7v and not with 5v , how can there be a break in the circuit.

What I mean by works is that the display shows what it should, and doesn't show anything with 5v.
If there is a break in the circuit, how could I find it and would it be easy to do with a mulimeter.

Thanks
Title: Re: MAX7219 problem
Post by: adwsystems on Apr 22, 2019, 06:11 pm
@Avalon. All of the information provided so far indicates that neither of you power sources you have used have the power (current capacity) to run the display, the Arduino and the rest of the modules.

It is 100% permissible to use multiple power sources so long as they have a common ground. Other than your RAVPower USB powered adapter, do you have another 5V output power supply available? I suggest, at least for testing/proof-of-concept/debugging, you connect power of the display to a separate common-ground power supply.

Additionally, to prove to yourself, the power of the display is causing your issue. Disconnect the display and modify your program to send the display data to the serial port and review it in the serial monitor. This will prove your sketch works without the display. Then connect the display to the power source and see if the serial data stops. Which means you have just overloaded the power supply and the Arduino shut down. That circles back around to the fact that your power source is not large enough. LEDs draw lots of current, need lots of power. If you don't supply it, the will try to get it and cause issues elsewhere.
Title: Re: MAX7219 problem
Post by: avalon66 on Apr 22, 2019, 06:56 pm
Yes I understand that not enough power is provided to run the display as well as the RTC and DHT.

I do have a 5v 6amp power supply with a barrel connector, which I could use.

Working it out how much power would be required for the led display, gives me 256 leds x say60mA per led = roughly 3amp?

I also have a 5v 2.5 amp power supply which I have been trying to get it to power everything before , but didn't.

Now, after days of trying this or trying that, the said 5v 2.5 amp power supply is actually powering the display now. And checking the voltage on the display , it is 3.5v.
I have also just tried the 5v 6 amp power supply and at first the display didn't light up, so I re inserted the barrel connector and the display is now working. **!! Again the voltage on the display is the same 3.5 volts.

I have no ide as to why the 5v 2.5 amp power supply did not power the display before, but it does now. Could the difference in voltage make that difference, ie 3.1v earlier and now 3.5v.

Thanks
Title: Re: MAX7219 problem
Post by: adwsystems on Apr 22, 2019, 07:12 pm
Where EXACTLY are touching each of the probes to the circuit to measure the 3.x volts? It can't be red on power and black on ground or the Arduino would not work. The running assumption is lack of correct use of the voltmeter in some way.

Generally a good rule of thumb is 20mA per LED. 256 * 0.060A = 15A. 256 * 0.020A = 5.1A 3A/256=0.011A (11mA). Not sure how you got 3A there. Which explains your lack of power. You need just the 2.5A power supply to run just the LED display. Then more to run everything else.

Title: Re: MAX7219 problem
Post by: avalon66 on Apr 22, 2019, 07:50 pm
The gnd probe was on the gnd of the motherboard, and the vcc probe was on a vcc wire of the display. To check, I also put the gnd probe on to the gnd pin on the pcb board, then the vcc wire on the display.

The Arduino does or did work ok when I measured the voltage.

To work it out I used this :
60mA per led x256 = 1.54A, But the the figure of 60mA is given for an led strip light, so maybe less for a display Then add another 1A or so for the other devices. 3A was just an exaggeration to be safe.

Strangely enough, the 5v 2.5 Amp power supply did actually run the display, but to be safe I am using the 5v 6amp pwer supply, which I bought for an led strip project, but didn't materailise.

Thanks
Title: Re: MAX7219 problem
Post by: adwsystems on Apr 22, 2019, 07:58 pm
256 x 0.060A still equals 15.4 amps. Not 1.54A. So you are doing 256 * 6mA (0.006). Explains a bunch.

You will need to provide model number of your display and a picture of you testing it. Based on the photo in post #16, it is impossible for Vcc of the display to be different than Vcc of the Arduino, and the Arduino will NOT work at 3.5V. Using one supply, it is impossible for the the 5V pin of the Arduino to be different from the Vcc for the display if they are directly connected together. Therefore the wiring you describe is not what you actually have. A picture is worth 1000 words.
Title: Re: MAX7219 problem
Post by: avalon66 on Apr 22, 2019, 09:08 pm
Yes you are right, 256 x0.060 is indeed 15.36A, so 15.4A then. Blimey, I didn't realise that the project would take over 15amps to run!!!

The display does not have a model number itself, but each mudule has this : 1088AS
The 5v 6A power supply is a Channel Well AC Adaptor , Model PAA030B 30watt.

Not being an EE, but an amateur, I am not sure I understand the part about the vcc of the display and vcc of the Aduino.

One picture is of the display showing scrolling text , and theother is of inside the box showing the wiring.

It has never been changed art anytimesince I put the project together, and I don't see why I would. I work on the ;principle of it's working, leave it alone.
Title: Re: MAX7219 problem
Post by: adwsystems on Apr 22, 2019, 10:14 pm
Chances are the current is 10-20mA per LED, or 3-5 amps total. Either way still WAY more than what you had.

Just follow the wires. Power goes into the connector then a wire on the circuit goes to the pin labelled 5V, then a wire goes from that pin to the display. No matter where you measure along a (short) piece wire, the voltage WILL be the same. The voltage WILL BE the same at both ends of a wire. It doesn't matter if you touch the 5V pin on the Arduino or the Vcc pin on the display. THEY MUST BE THE SAME. If they are different. Then you are either not connecting to the correct place or not telling us the place you are actually touching.
Title: Re: MAX7219 problem
Post by: avalon66 on Apr 22, 2019, 11:39 pm
Well as I said, the project is running fine now with a 5v 6amp power supply.

I put a red wire from my meter onto a vcc pin soldered onto a pcb board, then the gnd wire to any gnd points on the breadboard or gnd pin or gnd of the display, the reading was the same, nominally 3.5v.

I have attached a picture of the wiring I foloowed for the said project. Maybe that will tell you more than I can.

Thanks
Title: Re: MAX7219 problem
Post by: Jobi-Wan on Apr 23, 2019, 12:30 am
Yes you are right, 256 x0.060 is indeed 15.36A, so 15.4A then. Blimey, I didn't realise that the project would take over 15amps to run!!!
How many panels are we talking? Just 1 strip of 4 8x8 blocks?
Those have a duty cycle of 1/8. You have 32 on at a time at most.
With a generous 30 mA per LED, you get close to 1A not accounting for dead time.

I have one of those. I just tried and measured. With all LEDs on at highest brightness, it pulls just under 650mA. You can power it from a phone charger or a laptop USB port.
Title: Re: MAX7219 problem
Post by: Paul__B on Apr 23, 2019, 12:31 am
This is all getting a bit looney here!
(https://forum.arduino.cc/index.php?action=dlattach;topic=610613.0;attach=305102) (https://forum.arduino.cc/index.php?action=dlattach;topic=610613.0;attach=305102)

I keep seeing references to things such as
I have also just tried the 5v 6 amp power supply and at first the display didn't light up, so I re inserted the barrel connector and the display is now working. **!! Again the voltage on the display is the same 3.5 volts.
I cannot see in the photograph above, any "barrel connector" other than the useless one on the UNO.  You cannot power a project by this connector!  You probably can power it through the USB jack, but it would be better to connect a 5 V regulated power supply with whatever connector - I have pictured a couple - to the display and to the 5 V pin on the UNO.

I see two red wires joined passing from the UNO to the soldered breadboard - that join is the point at which a 5 V power supply must be connected (and of course, together with a corresponding "ground" connection).

Now just to assist adwsystems, the display in question is four modules of MAX7219 matrix.  This is a multiplexed display on each module of which only up to eight LEDs are illuminated at any one moment, even if every point on the display was active.  The drive current per LED is set at 40 mA - because they are only ever illuminated for one eighth of the time.

This means a display module could draw 320 MA if all are illuminated which you of course, never require.  So the maximum current draw here is 1.3 Amps.  If powered through the USB connector, if you did illuminate all LEDs, the polyswitch on the UNO would shut it down, but so long as no more than 40% of the LEDs are displayed, it will not shut down on this account.

So to reiterate in no uncertain terms:  Under no circumstances should the "barrel jack" on the UNO be used in an attempt to power the circuit.
Title: Re: MAX7219 problem
Post by: adwsystems on Apr 23, 2019, 02:14 am
Well as I said, the project is running fine now with a 5v 6amp power supply.

I put a red wire from my meter onto a vcc pin soldered onto a pcb board, then the gnd wire to any gnd points on the breadboard or gnd pin or gnd of the display, the reading was the same, nominally 3.5v.

I have attached a picture of the wiring I followed for the said project. Maybe that will tell you more than I can.

Thanks
According to the drawing you posted, you are use of the voltmeter is sketchy. Nothing in your system can run on 3.5V.
Title: Re: MAX7219 problem
Post by: avalon66 on Apr 23, 2019, 10:10 am
How many panels are we talking? Just 1 strip of 4 8x8 blocks?
Those have a duty cycle of 1/8. You have 32 on at a time at most.
With a generous 30 mA per LED, you get close to 1A not accounting for dead time.

I have one of those. I just tried and measured. With all LEDs on at highest brightness, it pulls just under 650mA. You can power it from a phone charger or a laptop USB port.
Yes the MAX7219 is 4 blocks or modules at 8x8 leds on each
Title: Re: MAX7219 problem
Post by: avalon66 on Apr 23, 2019, 10:38 am
Ok, apologies for wasting everyone's time with my problem, but I have now finally understood how to power the project.

I have a + wire from a female barrel jack to a vcc pin on the pcb board. This pin is next to the vcc pin and wire from the Arduino Uno. I then connected the gnd wire from the barrel jack to the gnd pin on the pcb board, which is next to the gnd wire to the Arduino Uno.

I am now using a 5v 2.5 amp power supply connected to the female barrel jack to power the project which is working.

When you say :
Under no circumstances should the "barrel jack" on the UNO be used in an attempt to power the circuit.

Do you mean this particular circuit, or any circuit.
Title: Re: MAX7219 problem
Post by: adwsystems on Apr 23, 2019, 11:47 am
There is no Vcc pin on a genuine Arduino. The are 3.3V, 5V, and Vin pins.

You don't have to read the schematics to see what each are for. Just the description of the board tells you
Quote
Vin: The input voltage to the Arduino/Genuino board when it's using an external power source (as opposed to 5 volts from the USB connection or other regulated power source). You can supply voltage through this pin, or, if supplying voltage via the power jack, access it through this pin.

5V: This pin outputs a regulated 5V from the regulator on the board. The board can be supplied with power either from the DC power jack (7 - 12V), the USB connector (5V), or the VIN pin of the board (7-12V). Supplying voltage via the 5V or 3.3V pins bypasses the regulator, and can damage your board. We don't advise it.

3V3: A 3.3 volt supply generated by the on-board regulator. Maximum current draw is 50 mA.

GND: Ground pins.
As you see, using the Vin pin or the barrel jack does the same thing. Both go through the regulator.

You can use the barrel jack to power the Arduino or is you are careful you can use the 5V pin. But if you use the barrel jack for power, your CANNOT use the 5V power to power anything else. The regulator between the barrel jack and the 5V pin has just enough to run the Arduino. Attaching anything to the 5V when using the barrel jack (or Vin in pin) causes the EXACT issues you have described.

If I was standing next to you, I would have reached over and yanked out the red wire connected to the 5V pin, 10 posts back.

Your power supply, which is 5V, should be connected DIRECTLY to both the Arduino and the display. The daisy chain you have, power supply to Arduino and the Arduino to the display, is causing your problem.
Title: Re: MAX7219 problem
Post by: avalon66 on Apr 23, 2019, 02:00 pm
I knew something would be wrong withe way I have it connected and working.

i am not seeing any problems, and I have not had it connected this way before. It was however connected to the vcc pin on the display, Then there was a problem.
 
If I pull out the red wire to the arduino 5v pin and connect the red wire from the power supply to the 5v pin on the arduino, how do I then connect directly to the display, use 2 wires??

Title: Re: MAX7219 problem
Post by: adwsystems on Apr 23, 2019, 02:31 pm
If I pull out the red wire to the arduino 5v pin and connect the red wire from the power supply to the 5v pin on the arduino, how do I then connect directly to the display, use 2 wires??
Yes. You have to.


I knew something would be wrong withe way I have it connected and working.

i am not seeing any problems, and I have not had it connected this way before. It was however connected to the vcc pin on the display, Then there was a problem.
Vin is the input power. I will admit the 5V pin is a bit confusing as it has two purposes. 5V is either 5V output when 7-12V is supplied to Vin or the barrel jack; OR 5V is 5V input to the board. As it is, putting the 5V power supply into the Vin pin is only causing you a voltage drop across the regulator that is between the Vin and 5V pins, that doesn't have enough voltage supplied to operate properly. Essentially, you are using the device (voltage regulator) out of its specified range.

All of the issues you describe point to one thing. The Arduino and display are not correctly connected to the power source. You need to pick one of the three power input points to use:
1. Barrel Jack
2. Vin
3. 5V

You can pick only one of the three to connect to. The other two will be unused.

If you have a 7-12V power supply, you can connect that to either Vin or the barrel jack. But you CANNOT connect the display to the 5V (output) pin, there isn't enough power.

If you have a (good) 5V power supply, you can connect that to both the display and to the Arduino 5V pin. You CANNOT connect that to Vin/barrel pin. Then you can connect the display directly to the power supply. Yes, the connection is a "V" on both the 5V and ground of the power supply.

The power supply 5V should be connected directly to:
1. Arduino 5V
2. Breadboard +
3. LED display Vcc

Ground should follow the same rules. This is the proper way to distribute power in most designs, direct connection of the power/ground pins of the load directly to the power source. This simplifies trouble shooting. You are now 48 posts into fighting a basic design technique.

If you have it working, then good luck on it staying that way. If you want to substitute luck for experience, then open your mind and update your design.

Title: Re: MAX7219 problem
Post by: Paul__B on Apr 23, 2019, 03:25 pm
You can use the barrel jack to power the Arduino or is you are careful you can use the 5V pin. But if you use the barrel jack for power, your CANNOT use the 5V power to power anything else. The regulator between the barrel jack and the 5V pin has just enough to run the Arduino. Attaching anything to the 5V when using the barrel jack (or Vin in pin) causes the EXACT issues you have described.
Which is to say, if you are going to do anything useful with the UNO (or Nano, Leonardo, Mega 2560), because anything useful requires connecting other devices, just forget the "barrel jack" and "Vin" pin exist!  :smiley-roll:

When you say :
Under no circumstances should the "barrel jack" on the UNO be used in an attempt to power the circuit.
Do you mean this particular circuit, or any circuit.
I believe this has been answered.  :smiley-lol:

Quote
5V: This pin outputs a regulated 5V from the regulator on the board. The board can be supplied with power either from the DC power jack (7 - 12V), the USB connector (5V), or the VIN pin of the board (7-12V). Supplying voltage via the 5V or 3.3V pins bypasses the regulator, and can damage your board. We don't advise it.
This from the Arduino literature is terribly misleading.  It is simply nonsense!  :smiley-eek:  But we - the users - are unable to correct it.
Title: Re: MAX7219 problem
Post by: avalon66 on Apr 23, 2019, 04:15 pm
I connect 2 red wires to the female barrel jack, correct or not.
Then connected 1 red wire to the arduino 5v, and the other red wire to the display. If the first one is not correct then this wil be also
I connected the black gnd wire from the female barrel jack to the gnd pin / socket on the arduino
Then I connected the male barrel kack of the 6v power supply and hoped. The display flashed on, then off .

Thanks
Title: Re: MAX7219 problem
Post by: avalon66 on Apr 23, 2019, 04:44 pm
If I was standing next to you, I would have reached over and yanked out the red wire connected to the 5V pin, 10 posts back.

I wish you were standing next to me then you could see what I w as doing and then correct me.
Title: Re: MAX7219 problem
Post by: adwsystems on Apr 23, 2019, 05:02 pm
I connect 2 red wires to the female barrel jack, correct or not.
Then connected 1 red wire to the arduino 5v, and the other red wire to the display. If the first one is not correct then this wil be also
I connected the black gnd wire from the female barrel jack to the gnd pin / socket on the arduino
Then I connected the male barrel kack of the 6v power supply and hoped. The display flashed on, then off .

Thanks
Where did you get a 6V power supply? Typo? Per you reply in post #48, you are using a 5V 2.5A power supply.

It is no surprise to me that it did not work. The instructions in post #48 have not been followed.

I will summarize.

You can only use one of the three following connections:
1. Barrel Jack (for 7-12V power supplies)
2. Vin (for 7-12V power supplies)
3. 5V (for 5V power supply)

Pick the one that fits.

Per your reply as post #45, you are using a 5V power supply. Therefore you CANNOT use the Barrel Jack and you CANNOT use Vin. You can only connect to 5V pin. That will only power the Arduino.

Now you have to get 5V power from the power supply to the LED display and to the breadboard. Make the connections and send us a picture of your solution.

Title: Re: MAX7219 problem
Post by: avalon66 on Apr 23, 2019, 05:30 pm
It was a typo,. sorry

What is a 5C power supply, as I can't say i've heard of them.

Ok if I use a 5v power supply which has a barrel connector, and plug that into the female jack plug on the arduino,  how do I get a 5v supply to the display
Title: Re: MAX7219 problem
Post by: adwsystems on Apr 23, 2019, 05:46 pm
What is a 5C power supply, as I can't say i've heard of them.
It was a typo,. sorry. Fixed.

Ok if I use a 5v power supply which has a barrel connector, and plug that into the female jack plug on the arduino, which now does not power the display, but did so yesterday, how do I get a 5v supply to the display
What is the voltage requirement for the barrel connector and the Vin pin? I have listed it at least three times. Then return to Paul__B post #23 for your answer.

Per your reply as post #45, you are using a 5V power supply. Therefore you CANNOT use the Barrel Jack and you CANNOT use Vin. You can only connect to the 5V pin. That will only power the Arduino.
Title: Re: MAX7219 problem
Post by: avalon66 on Apr 23, 2019, 06:24 pm
So I can use a 7v to 12v on the barrel socket/connector, and the Vin is the same from what I have read.

Alright then, I will use a 7v power supply, and I have a 5v wire to the display, which gives 5v, well 4.92v , on the display.
Title: Re: MAX7219 problem
Post by: adwsystems on Apr 23, 2019, 06:34 pm
So I can use a 7v to 12v on the barrel socket/connector, and the Vin is the same from what I have read.

Alright then, I will use a 7v power supply, and I have a 5v wire to the display, which gives 5v, well 4.92v , on the display.
You will be working with two powers upplies which means you MUST connect the grounds together (at some point) or you will run into a whole new set of issues.
Title: Re: MAX7219 problem
Post by: avalon66 on Apr 23, 2019, 06:39 pm
You will be working with two powers upplies which means you MUST connect the grounds together (at some point) or you will run into a whole new set of issues.
Two power supplies?
I just said i'll use a 7v power supply, only 1. The 2 grounds are together
Title: Re: MAX7219 problem
Post by: adwsystems on Apr 23, 2019, 06:55 pm
So I can use a 7v to 12v on the barrel socket/connector, and the Vin is the same from what I have read.

Alright then, I will use a 7v power supply, and I have a 5v wire to the display, which gives 5v, well 4.92v , on the display.
When you wrote this I assumed (I know, I made an ass out of me, at least), that you were going to use the 7V in the barrel jack and the 5V for the display.

Based on this

Two power supplies?
I just said i'll use a 7v power supply, only 1. The 2 grounds are together
I was wrong. You actually intend to ignore all the posts go back to what didn't work and have been told won't work.

So I will write this again.

You can only use one of the three following connections:
1. Barrel Jack (for 7-12V power supplies)
2. Vin (for 7-12V power supplies)
3. 5V (for 5V power supply)

PICK ONE and ONLY ONE.

Based on my new understanding of this post
Alright then, I will use a 7v power supply, and I have a 5v wire to the display, which gives 5v, well 4.92v , on the display.
You are going to use two of the three pins. You intend on using both the barrel jack and the 5V pin. THAT WON'T WORK.

You need 7-12V to use the barrel jack. You need 5V to run the display. The 5V pin of the arduino does not provide enough power to run the display. You already figured that out.

Plug the 7V supply into the barrel jack. Plug the 5V supply into the display. Connect the grounds. DONE. PROBLEM SOLVED. Your do-dad works.
Title: Re: MAX7219 problem
Post by: Paul__B on Apr 24, 2019, 12:02 am
I have said it in post after post, most recently in #49.

If you do not believe me, well, we await #99.  :smiley-roll:

So I will write this again.
You can only use one of the three following connections:
1. Barrel Jack (for 7-12V power supplies)
2. Vin (for 7-12V power supplies)
3. 5V (for 5V power supply)
PICK ONE and ONLY ONE.
I really wish you would not confuse the poor fellow with such unhelpful nonsense!  :smiley-eek:
Title: Re: MAX7219 problem
Post by: adwsystems on Apr 24, 2019, 01:55 am
Quote
You can only use one of the three following connections:
1. Barrel Jack (for 7-12V power supplies)
2. Vin (for 7-12V power supplies)
3. 5V (for 5V power supply)
PICK ONE and ONLY ONE.
I really wish you would not confuse the poor fellow with such unhelpful nonsense!  :smiley-eek:
What are you talking about, Paul ? ? ? ? ? ? ? ? ?

What about this is do you not find correct?

Are you saying it is possible to supply power to more than one of these pins at once?

Is the barrel jack and Vin pin not for the input of 7-12V power?

Is the 5V pin not the input for a 5V power source?

If you put power into the first two, 5V will be present on the 5V pin but not with any capacity to do anything. So how is it not correct that only one of the three pins can be used at once?

You have not indicated what you feel is misleading about
Quote
5V: This pin outputs a regulated 5V from the regulator on the board. The board can be supplied with power either from the DC power jack (7 - 12V), the USB connector (5V), or the VIN pin of the board (7-12V). Supplying voltage via the 5V or 3.3V pins bypasses the regulator, and can damage your board. We don't advise it.
Besides the lack of a caveat to indicate the 5V available is not able to power anything of consequence.
Title: Re: MAX7219 problem
Post by: Paul__B on Apr 24, 2019, 10:01 am
Besides the lack of a caveat to indicate the 5V available is not able to power anything of consequence.
Yes, you finally "got it".  That was exactly my complaint.  :smiley-lol:

The fellow appears to be having trouble comprehending that single detail.  Under the circumstances, and in particular that he is wishing to power something "of consequence", I feel that we need to be consistent in advice and not favour recidivism in any form.

Totally forget the "barrel jack" and "Vin" - never even mention them as possible options.

Even if you feel that they might be usable when someone has a UNO (or my preference: Nano) and nothing else beyond a few indicator LEDs and resistors, I think the requirement for a 5 V power supply - and I cannot say this too often; "phone chargers" are by far the most readily available option - should be emphasised as the preliminary basis of any further progress.
Title: Re: MAX7219 problem
Post by: adwsystems on Apr 24, 2019, 12:10 pm
Yes, you finally "got it".  That was exactly my complaint.  :smiley-lol:

The fellow appears to be having trouble comprehending that single detail.  Under the circumstances, and in particular that he is wishing to power something "of consequence", I feel that we need to be consistent in advice and not favour recidivism in any form.
Please reread and dwell on my statement.
Quote
You can only use one of the three following connections:
1. Barrel Jack (for 7-12V power supplies)
2. Vin (for 7-12V power supplies)
3. 5V (for 5V power supply)
PICK ONE and ONLY ONE.
We are talking apples and oranges. I am talking power in. You are talking power out. Your complaint has nothing to do with what I am saying. I am saying to choose one of the three power inputs and you are "confusing" issues by including power output (ie., using power from the 5V pin). I never said to use the 5V power out.

The instructions above are simple and perfectly clear. Choose one of the three and forget the other two exist. No matter what design choice is made, it is not possible to follow the instructions and to use 5V as a power output. To do so means either there is not power applied to the barrel jack or Vin (use only one and you selected 5V to be used as an output) or you have connections to two of the three. Either way you are not following the instructions.

The 5V pin as a power source (out) is useless. On that we agree.

Totally forget the "barrel jack" and "Vin" - never even mention them as possible options.

Even if you feel that they might be usable when someone has a UNO (or my preference: Nano) and nothing else beyond a few indicator LEDs and resistors, I think the requirement for a 5 V power supply - and I cannot say this too often; "phone chargers" are by far the most readily available option - should be emphasised as the preliminary basis of any further progress.
Well, we will have to agree to disagree on this point. The ability to have a flexible voltage input is quite useful.

My complaint is the fact they recommend 9V and built the regulator limit to 12V. I don't like running things (electronics) at there design limit. Who does? Furthermore, what the #!@$ heck runs on 9V? How many devices out there run on 9V? There are tens of magnitudes (10-1000000x) more devices available that run on 12V then on 9V.
Title: Re: MAX7219 problem
Post by: Paul__B on Apr 24, 2019, 02:07 pm
We are talking apples and oranges. I am talking power in. You are talking power out. Your complaint has nothing to do with what I am saying. I am saying to choose one of the three power inputs and you are "confusing" issues by including power output (ie., using power from the 5V pin). I never said to use the 5V power out.
...
The 5V pin as a power source (out) is useless. On that we agree.
Yes, of course I am talking about "power out" if that is the thing that is required to complete a project as in this particular case.  If you need 5 V for a purpose and the Arduino cannot be used as a source of 5 V, then a power source that will not provide that 5 V is simply not relevant; not an option.

Your stance is very peculiar, since you appear to keep criticising the use of two separate power supplies, but powering the Arduino via the regulator at 9 V mandates a second supply for the 5 V yet you are suggesting that it is "possible" to use a 9 V input.

How many devices out there run on 9V?
In my experience, most cordless phones, older telephone modems (when these were a meaningful device) and ADSL boxes, network devices, Ethernet hubs, toys, radios and many others.

These are the things that were contemporaneous with the original Arduinos, so Arduino made use of the available power packs.
Title: Re: MAX7219 problem
Post by: adwsystems on Apr 24, 2019, 07:24 pm
Your stance is very peculiar, since you appear to keep criticizing the use of two separate power supplies, but powering the Arduino via the regulator at 9 V mandates a second supply for the 5 V yet you are suggesting that it is "possible" to use a 9 V input.
Where and what are you talking about? ? ? ? When ever did I mention using multiple power supplies? I don't care how many power supplies you have so long as you follow the instruction. Please tell me how you can connect multiple power supplies to the Arduino and still follow the instruction.

Here is the instruction for your reference
Quote
You can only use one of the three following connections:
1. Barrel Jack (for 7-12V power supplies)
2. Vin (for 7-12V power supplies)
3. 5V (for 5V power supply)
PICK ONE and ONLY ONE.
I don't care how you use the pins so long as you follow the instructions. If you choose to use the barrel jack, you cannot use the 5V pin as power source as that will violate the instruction. If use use the 5V pin as a power source and follow the rule then the board has no power. So the instruction inherently prevents the 5V pin from being used as a power source.

You will have to explain very clearly how this contradicts anything you have said or any good (Arduino) design practices.