I built a project last year using a MAX7219 4 segment display with buttons, a DHT22 and a DS1307. Very recently the display stopped working so I re installed the sketch and the display worked again for about 5 / 10 minutes, then went off again.
At this point I wasn't sure if it was the actual display or the Arduino itself, so I tried 2 other displays, with the same result.
I then stripped down the arduino to just a display which only the first 2 segments work
I have checked the 5v pin on the arduino and it is close enough at 4.95v. When I attach 2 jumper wires to the project board, measuring the voltage on a breadboard only shows 3.3v. And this is from a 9v battery connected to the VIN pin on the arduino, as the project itself runs from a 9v 2amp power supply.
Re-connect it to a proper power supply.
The 9 volt square batteries dont always work too well with Arduino projects as they dont give enough current and dies quickly.
This would be more true with lots of LED's
I was initialy powering everything with a 9v power supply, but something went wrong as the power leads from the display got hot and the plastic ends of the jumper wires melted. Consequently the display stopped working
Now with just a display connected, using a 5v power supply, all 4 segments light up, but when I use a 9v power supply the display comes on, then off again. The vcc line from the display is connected to the 5v pin on the arduino
On the Arduino Uno clone I am presently using, I found that the barrell connecton on the board is wobbly, in that it moves from side to side , and the connection is lost sometimes.
The other original Arduino Uno I was using which suffered the breakdown as it were, is a genuine Arduino Uno, or at least it looks like it is a genuine one. This one does not power up through the barrel connection with either 5v or 9v.
Powering the display from a separate 5v source is a bit impractica as that means 2 power supplies are required.
Do not use the Barrel jack to attempt to power an Arduino for any serious application (which is to say, when connecting anything else to the Arduino board itself).
It is simply not appropriate. Unfortunately, many "tutorials" including the Arduino site references are misleading. If your Barrel jack is loose you might as well remove it and throw it away. You do not need it!
avalon66:
I was initially powering everything with a 9v power supply, but something went wrong as the power leads from the display got hot and the plastic ends of the jumper wires melted. Consequently the display stopped working
Clearly you short-circuited the power connections (or connected them in reverse perhaps). That is an entirely separate blunder to use of the Barrel jack, Whether you have permanently damaged either Arduino or display (perhaps not if it actually lights up) is not clear from your description.
sterretje:
My question is what to do when you want to upload? Leave as is and connect the USB? Or disconnect the 5V and use the USB?
Disconnect the 5 V.
The latch line of the MAX7219 should have a 10k pull-up to 5 V. This will prevent the display showing random data on start-up so the display will draw minimal current.
Frankly, the only concern about havig a 5 V supply conencted when you use the USB is the concept of "fighting" relating to the possibility that the additional power supply may feed current back into the USB power of the PC and this has in some cases been reported to damage the PC or laptop. Clearly you would not want the external power supply to be powered if the PC is not.
How likely this is, is extremely dubious as it turns out that the vast majority of powered USB hubs do precisely this, and without a polyfuse as protection, as all 5 V lines in these hubs connect directly together. There seems to be little report of this ever causing damage.
The latch line of the MAX7219 should have a 10k pull-up to 5 V. This will prevent the display showing random data on start-up so the display will draw minimal current.
Frankly, the only concern about havig a 5 V supply conencted when you use the USB is the concept of "fighting" relating to the possibility that the additional power supply may feed current back into the USB power of the PC and this has in some cases been reported to damage the PC or laptop. Clearly you would not want the external power supply to be powered if the PC is not.
How likely this is, is extremely dubious as it turns out that the vast majority of powered USB hubs do precisely this, and without a polyfuse as protection, as all 5 V lines in these hubs connect directly together. There seems to be little report of this ever causing damage.
Thanks. The worry about feeding into each other is the reason that I use a (powerful enough) 5V supply in led strips projects and use a small DC-DC converter to up-convert that 5V to create 9V for the Arduino. That way I don't have to worry about feeding each other (at least on Uno/Mega).
When I feed the arduino cone with USB power and the project board connected, the MAX7219 4 segment display does not light up.
I have a 10k resistor on the CS line of the display, but without the resistor it does light up and shows the zero digit on the first segment. The remaing 3 segments are lit but no digits are showing.
The same results are true when using a 5v power supply.
Using a 9v power supply with the 10k resistor, the display lights up initially, but then goes just 1 line of leds flashing on/off on the first 3 segments and on on the last segment the flashing leds are moving/scrolling up .
Is the MAX7219 4 segement led display fauty now.
The whole project consists of buttons, RTC DS1307, DHT22 and a MAX7219, and I thought I could use a 9v suppy connected to the Vin pin, as it is a standalone project
avalon66:
The whole project consists of buttons, RTC DS1307, DHT22 and a MAX7219, and I thought I could use a 9v supply connected to the Vin pin, as it is a standalone project
You really need to forget about the "Vin" pin or "barrel jack". Failure after the regulator has had time to heat up is telling you this is the problem.
You need to start with just the Arduino and the display, powered either by an adequate USB supply given that the MAX7219 will not draw more than 360 mA of the USB's available 500 mA, or with an adequate regulated 5 V connected together to the display and the 5 V pin. Once you have that operating reliably with a test routine, you can consider adding the other parts.
The 10k as a pull-up will not hinder anything, it is merely a convenience in initialising. If it appears to do something contrary, you have a wiring mistake.
Sorry, but the experience of most of us here (who are "advising") is that in the vast majority of cases, the displays work just fine if you connect, power and code them correctly.
I have the display working fine now on the project board, and displays all the data from the sketch..
As it presently running from a usb connection from my pc and I need it to be a standalone in a box I made for it, how best shoud I power it; ie from a long usb printer cable plugged into a usb adaptor plug, or use a 5v power supply into the barrel jack.
