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Topic: MAX7219 problem (Read 1 time) previous topic - next topic

BJHenry

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.

Paul__B

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.



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  Unfortunately, many tutorials or "instructables" are seriously outdated or misleading and have not been updated to reflect the contemporary situation.


avalon66

#17
Apr 20, 2019, 10:39 am Last Edit: Apr 20, 2019, 11:59 am by avalon66
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

BJHenry

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.

Paul__B

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.

avalon66

#20
Apr 20, 2019, 07:36 pm Last Edit: Apr 20, 2019, 09:26 pm by avalon66
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/

Paul__B

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.

avalon66

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


Paul__B



Unfortunately, the "MyVolts Website" 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.


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.

avalon66

#24
Apr 21, 2019, 01:31 pm Last Edit: Apr 21, 2019, 02:05 pm by avalon66
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/

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


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.

Paul__B

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.

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.

avalon66

#26
Apr 21, 2019, 05:10 pm Last Edit: Apr 21, 2019, 06:08 pm by avalon66
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.




Paul__B

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.

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.

avalon66

#28
Apr 22, 2019, 10:37 am Last Edit: Apr 22, 2019, 12:02 pm by avalon66
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


Paul__B

So you are saying there is a missing connection somewhere between the breadboard and display?

You last posted this "diagram":


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



So where on this are these voltages?  When you say it worked and then "went off", did the Arduino pilot light dim?

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