FC-16 Led Matrix Modules and SPI not working when using Power jack

Projects Networking, Protocols, and Devices
1

Using an arduino Mega i can succesfully control two FC-16 modules via SPI interface only if arduino is powered by USB connector. When i try to use the power jack instead of the usb connector , led's modules don't work.

For these modules i use an external power supply that gives 5V. (Ground connected togheter). I tried to add pull-up resistor ( CS pins and MOSI Pin ) but anything changed.

Maybe different Voltage values? I tried to apply 5.5V instead of 5V and they start working, but that's the limit for these kind of modules and i would like to keep the voltage as low as possible.

I just can't understand what's happening!!

Note: No other SPI devices are connected

2

For these modules i use an external power supply that gives 5V.

On the power jack the minimal voltage is 7V. The internal voltage regulator has a minimal voltage drop of about 2V so anything below the 7V results in a too low voltage for the Arduino.

3

Thank you for your reply.

I didn't specify that i use two different power supplies. (grounds connected together)

The first one gives 5V to led's matrices and the second one gives 12V to Arduino. (only when USB cable is not plugged in)

4

Post a complete wiring diagram of the setup when not connected by USB.

5

This is what i did.

If the USB cable is not connected i switch on the Arduino with the lever switch.

diagram.png
diagram.png1600×973 62 KB

6

Did you check the polarity of the power supply connector? If you're running on the power supply, what voltage do you measure from GND to the 5V pin on the Mega?

7

Yes i did. I measure exactly 5 Volt.

What do you think about adding a resistor in series on each wire of the SPI bus, in order to cause a voltage drop? Maybe the voltage coming into the led module is too high compared to their VCC voltage... I could try to do it. Do you know how much current will flow during a communication?

8

What do you think about adding a resistor in series on each wire of the SPI bus, in order to cause a voltage drop?

I doubt that this will change anything.

Are the modules really wired as in the wiring diagram? As far as I know the modules you should connect the MOSI to DIN of the first module and then DOUT of that module to DIN of the next module and so on.

Please upload a blink sketch to the Mega (without connecting the FC-16 modules). Check if it's blinking if powered by USB and if powered by the power supply. Post the results.