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Topic: Arduino start up problem (Read 95 times) previous topic - next topic


May 05, 2019, 02:39 pm Last Edit: May 05, 2019, 04:49 pm by BrianL
I have a Uno working a Max 72XX display consisting of 8 blocks (each block 8 x 8 ).
The Uno data is from a pre prepared sketch from Parola_Scanning.  It loads correctly and the Uno/MAX72xx all work as expected, but only once the Uno starts.   The whole lot is powered from a separate power source - Iphone USB charger providing 5 volts. The power is inputted via a separate 2.1mm DC socket which is connected to the underside of the Uno boards DC input jack pins, but as the MAX72xx takes more power than the Uno can provide therefore the positive power (VCC) for the MAX72xx is taken directly from the underside of the Uno by soldering feed wires to the Uno's DC socket pins thereby providing a direct 5volt feed to the displays VCC and to the Uno itself.
The displays GND connection is from the Uno 'Power GND' pin.  The MAX72XX data connections are CLK, CS and DIN and are directly connected from the Uno 13 (CLK), 11 (DIN) and 10 (CS) pins.  Connections on the Uno are all soldered and are not relying on the plug in connections.

On applying DC power the whole display lights sequentially, with all LED segments light. Solid blocks of red LEDs appear one after the other until all 8 blocks are lit and they remain like this.  Pressing the Uno Reset button doesn't do anything.  However and occasionally handling the Uno causes the Uno and display to work correctly! (Perhaps a clue to something possibly?).

Plugging in the USB lead and connecting it to a PC but no programme immediately causes the scrolling text on the MAX72xx to work correctly.  Remove the USB cable and the Uno remains working correctly and continuously as expected. 

Any ideas what may be the cause?

Photos attached are the soldered power input and display connections. The display at power up and the display working correctly once the PC/USB cable has been connected


Found the problem.... Power supply was intermittently faulty.   Phew!

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