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

avalon66

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.

Paul__B

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?

avalon66

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

adwsystems

@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.

avalon66

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

adwsystems

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.


avalon66

#36
Apr 22, 2019, 07:50 pm Last Edit: Apr 22, 2019, 07:53 pm by avalon66
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

adwsystems

#37
Apr 22, 2019, 07:58 pm Last Edit: Apr 22, 2019, 08:06 pm by adwsystems
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.

avalon66

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.

adwsystems

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.

avalon66

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

Jobi-Wan

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.

Paul__B

#42
Apr 23, 2019, 12:31 am Last Edit: Apr 23, 2019, 12:33 am by Paul__B
This is all getting a bit looney here!

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.

adwsystems

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.

avalon66

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

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