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As part of a Simhub Dash set up I have been trying to get a 8 Digit 7 segment display working on an Arduino Nano. As part of my fault finding process I have gone back to basics and am using the 7CDemo7Segment example script included with the ledcontrol library . The 8x8Matrix Test is performed with the LCDemoMatrix example script. Both displays are powered by the 5v/Gnd pin combination. No other devices are connected.

The following image shows the circuit. Ignore pins (they are as described below) and Uno/Nano are interchangeable.

enter image description here

Completing the following tests I get the described results:

  • Uno and 7Seg with Pins 678 - OK - proof of library and display
  • Nano and 7Seg with Pins 678 - FAILS (nothing lights up and if it does it’s incoherent to what it should be going) - same code and display
  • Nano and 8x8 Matrix with Pins 678 - OK - proof of the Nano and Pins.

I feel the above combinations prove that: the script is correct; the display works; and that the pins are okay.

The only thing I can think is that this is a power/current issue via USB/5V pin?

Would someone be able to confirm. I have looked at How much current can I draw from the Arduino's pins? and feel that there is not a clear answer for the Nano 5V pin.

Byte Insight
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    With out a schematic we can only guess (or ask a lot of questions). The Atmel328 processor can handle up to 40mA per pin. But when you add all the current up you should stay below 200mA. So, lets say your properly current limited LEDs are suppose to draw 5mA each. Then, you should not turn on more than 40 on at the same time. But I suspect you have other problems. You might be trying to run multiple programs which use the same resources. For example, you may have a limited number of timers and one program may overwrite the settings of another. Thereby ruining the other's LED control. – st2000 Mar 14 '22 at 12:40
  • @st2000 I have tried to update the question without (hopefully) adding too much unnecessary detail. – Byte Insight Mar 14 '22 at 13:36
  • So, there is only the 1 display? Can you also identify the software library (or libraries) you are using? From the wording in your question I though you had several different displays that worked independently but not together. – st2000 Mar 14 '22 at 14:11
  • Honestly I don't think power is the issue. When powering via USB you should be able to draw the full 500mA, that the USB port gives you. Thats way enough for a normal 7 Seg display, even with 8 digits. Bit you can test this by connecting both Arduinos via USB and then connecting their ground and 5V. That doubles the available current – chrisl Mar 14 '22 at 14:29
  • Please provide a link to the library that you are using – chrisl Mar 14 '22 at 14:31
  • Power requirements of a 7 Segment Display on Uno vs Nano ... they would be the same – jsotola Mar 14 '22 at 16:18
  • Does the voltage regulator on the Nano get hot? – VE7JRO Mar 14 '22 at 19:51
  • What do you mean by "FAILS"? Please be more specific on the failure, what do you get instead of your expectation? – the busybee Mar 15 '22 at 06:52
  • @st2000 Yes, eventually both should be connected but for the purposes of understanding this problem on a single display is connected – Byte Insight Mar 15 '22 at 10:48
  • Thanks for answering. Know this, loading up more than one library or loading up a library intended for a different processor can lead to difficulties. For example, 2 libraries may try to configure the same timer, interrupt or processor pin. Likely this will lead to unexpected results. Can we assume you are loading up only the led control library? – st2000 Mar 15 '22 at 12:42
  • Yes. I’m using the built in library examples and just changing the pins as appropriate. In my mind it really could not be simpler. – Byte Insight Mar 15 '22 at 22:02

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