Hi there!
I started this new topic because I have questions which are related to two different arguments which I always found discussed separately but after I merged them into my project I found an annoying problem.
My arduino is contolling three max7219 and is reading inputs from two 4021. So I used three digital pins for the three chained 7219 and three pins to read inputs from the two 4021 which are chained as well.
I'm controlling everything with maxMsp and booth inputs and outputs work perfectly, so there are no wiring mistakes. I added all the capacitors needed for the three 7219 but I didn't use any transistor because since they work fine even without it.
The problem is the following:
If I open my max patch and I press the 16 buttons on my hardware, on the patch I see that everything works perfectly. But, If I ligth up some led (from the patch) or even just one the patch does not get the status of my 16 inputs any more.
I also tryed to have the leds controlled just by the code inside the board which makes some led blinking. Even in that case the max patch doesn't get the signals from the shiftin.
At this point I thought that, since arduino needs to comunicate fast with the 7219, there could be some speed problem in receiving inputs from the 4021, but only from them becouse other inputs works fine. This seems strange to me because TX data generally doesn't create problem to RX data.
My question is: does anyone of you knows if arduino have this kind of problem in managing inputs and outputs?! Or is it just a problem of code and I'am so dumb?