So I was trying to turn on my project today and the board short circuited. After the short the program would reboot like a restart.So after looking at the circuit for a while I moved two wires around. I tried again and the arduinos shorted again but this time wouldn't turn back on. Now the ON , TX, RX, L LEDs keep blinking fast and I don't know what this means. Here are the details:
I am working on a school project for engineering. Our group was tasked with making a pop-a-shot basketball arcade game. The program counts down from 60 and keeps track of score with a vex limit switch hooked up below the hoop. We have one arduino (Uno) that outputs a 1 or 0 every second on its pin 13 then that goes into pin 10 of the other arduino (mega). Yes, we do have a common ground and the power before I switched the wires was coming from 5v on the Mega to the Vin pin on the Uno. Pins 22-20 are used for large SSDs (Seven segment displays), which require I believe 20 mA for each segment on each SSD (total should be 560 mA(we are not using the decimal on the SSDs)). The problem is that the power is coming from a 15v jack and that is hooked up to a switch. Whenever I turn the switch the arduinos won't power up, but when I power them separately they have those fast blinking lights which I have never encountered before. i tried doing some digging but I couldn't find anything. If you need to know any more information please ask I am on break right now and will most likely be working on it most of the time. If you need to know about the other pins on the Mega 2-8 are regular LEDs and same with 50-54.
Several red lights come on in my mind when I read this story.
So the Mega powers the four displays directly?
One pin can switch 20mA, but that doesn't mean that the package can handle 560mA.
Read chapter 31 of the Atmega 2560 datasheet.
Never directly connect two Arduinos when there is a chance that one will be off.
Always use a 4k7 or 10k resistor between pins.
Phantom powering (powering the one that's off through the input pin protection diodes) can destroy the pin.
The onboard 5volt regulator will have trouble powering the Mega alone with 15volt on the DC socket.
An exta 100mA will overheat the regulator and the Mega will shut down (if you're lucky). Worse for the Uno.
"the power before I switched the wires was coming from 5v on the Mega to the Vin pin on the Uno."
Wrong. The Uno would have had 4volt on the 5volt rail. Vin is before the onboard 5volt regulator.
I would like to see a diagram before going any further.
Leo..
Thank you for your input! it was very helpful. I am working on a diagram right now I was stupid and let my group tape everything down before I got where each wire explicitly goes. I can tell you what wires go to which power and ground but as fore ABCDEFG on the SSDs I would have to spend a little more time on that. It will take me few few minutes before the diagram is don. When it is I'll post on my topic as a reply Thank you!
The Mega can't sink that much current.
Loose the Mega.
The Uno can do all of this with the help of four shift registers, one per 7-segment display.
I would use the Uno and four TPIC6C595 (or TPIC6C596).
Easy to solder four TPIC6C595 on a piece of veroboard, or use these:
There might be other ways.
Maybe someone else will chime in.
What is the forward voltage of one segment of your display, or how many LEDs in series per segment.
12volt regulated might be enough with these shift registers (lower losses).
The Uno will be happier with <=12volt on the DC jack.
Leo..
Sorry I need to make an edit to my original post it si supposed to be pins 22-49 are used for large SSDs not 20-22
Don't PM. Please ask questions here, so we can all learn from it.
A shift register uses three pins of the Uno.
Many can be daisy-chained.
So four big displays still only use three pins (and a 5volt and ground wire).
If you mount the shift register boards near the displays, you only need 5wires between the display and the Uno.
A Cat-5 cable could work.
Leo..
I don't know if you need to see the code right now but in it we coded a display driver. I attached a potion of the driver. It has multiple tabs and is really long since it needs to go to 99 so I only attached 21-30. I am a novice at this so my next question is would I have to change the code? I have barley used shift registers. I have only used one sample programs and I built a partial binary counter with it. Also, the UNO has I believe 13 or 14 input/output pins so I would need more pins because I have 10 regular LEDs and I am working on a radio frequency controlled controller for the game so people can choose between different modes, but anyway, the controller would need one pin so total I/O pins needed would be 16 including the clock. So, could I do what you're suggesting with the MEGA instead?
DisplayDriver2130.ino (1.14 KB)
Also, I know how I would power the large SSDs... I would plug in a 12-15v barrel jack into the arduino then use the Vin pin to get that power to the SSDs, how would you suggest powering them?
Vin is 0.7volt less than the DC jack, because of a reverse protection diode.
That diode also has a limit of 1A
Why not use two supplies. A 12-15volt (regulated) supply, only for the display (LED anodes).
And a small regulated 9volt supply for the Arduino (DC jack).
A 5volt phone charger with USB socket (use USB lead) will also work.
Share supply grounds.
The shift register chips are powered from Arduino's 5volt pin, but only use a few milliamps.
Had a quick look at the Sparkfun example code (post#4).
Not a programmer, but it seems you only have to enter the number to display in this line in void loop()
showNumber(number);
So
showNumber(47); // should display 47
The rest of the code takes care of the shifting.
Leo..
Thank you!!! You have been a huge help! One last question and this is the most important... Are the arduino boards O.K? The ON light keeps blinking so I assume that means it is turning off and on. Are the boards fried? The UNO appears to work when I power it by itself but when I try to power it with the MEGA the ON light on both boards blinks. When I power the MEGA by itself I doesn't do anything except blink.
Test the boards by uploading a simple sketch from the IDE.
"Blink" is sometimes used for that.
That only tells you if uploading to, and the core is working.
Use one that prints something to the serial port.
It doesn't use the regulator untill you run it on external power (DC jack).
And it doesn't tell you if all the outputs are working.
Test a few with a LED/resistor and the blink sketch (change pin number).
If a few a re working, the rest might still be ok.
You didn't stress one port, just the whole package.
Leo..
I may have chimed in a bit late, but I used my UNO with a 4 digit 7 segment display with no shift registers.
Look at this library: GitHub - DeanIsMe/SevSeg: Seven segment display controller library for Arduino
I created a countdown timer with start/stop and timer increment/decrement buttons all with no interrupts and it works great. I based what I did on an example sketch that came with the library.
From what I read about the project, this could very easily be done with just an UNO. I did use all the digital pins for the display, but used the analog pins for my inputs (setting the PIN_MODE appropriately of course 
).
I used that instead of a shift register because I it was a quick project and I had to use a tiny breadboard on a proto shield for a kind of prop for a skit.
But I agree that a shift register driving the display would be better solution if you needed more pins for other things.
Hope that helps!
I think OP mentioned LARGE scoreboard 7-segment displays, 15volt/560mA.
Leo..