8x8 LED Matrix

I was following this tutorial:

http://playground.arduino.cc/Main/DirectDriveLEDMatrix

I tried both sets of code, neither work. The second one's error is:

Output:

sketch_apr20a.ino: In function 'void setup()': sketch_apr20a:95: error: 'FrequencyTimer2' has not been declared sketch_apr20a:97: error: 'FrequencyTimer2' has not been declared sketch_apr20a:99: error: 'FrequencyTimer2' has not been declared

Sample code for scrolling messages (needs FrequencyTimer2 library):

Looks like you didn't download the library, or you didn't install it in the first place, or you didn't restart the IDE.

Thanks, I didn't know that. Would you recommend using resistors?

Would you recommend using resistors?

Always. For what?

Definitely with that circuit.

Would you recommend using resistors?

If you are following the tutorial you will have seen

Note: DON'T FORGET CURRENT-LIMITING RESISTORS.

I'm new to electronics. I know what resistors do, what don't understand why they're needed, or how you know if they are. I was running all lights on this thing without resistors and it worked fine? I ran it for at least 45min.

tylerv: I'm new to electronics. I know what resistors do, what don't understand why they're needed, or how you know if they are. I was running all lights on this thing without resistors and it worked fine? I ran it for at least 45min.

The reason you need current limiting resistors is that LEDs have an approximately constant voltage drop across them, of about 1.5-3.5 V (depends on the colour and type), if you apply 5 V directly from your Arduino, then you are forcing the remaining voltage to be dropped by the diode, and so it draws a very high current, if you keep doing this with too high voltages for too long, you will blow your LEDs. If you put a resistor in series with the LED then the remaining voltage is dropped across the resistor, and this voltage drop (about 3.5V) divided by the resistance you use will tell you your current through the LED. It varies between LEDs but it is usually advised to keep this below 15 mA

if you keep doing this with too high voltages for too long, you will blow your LEDs.

But long before that, you are going to blow up your Arduino. It is not intended to provide more than 20 mA of current per pin for very long. And, never more than 40 mA.

I always have my Arduino on 3 volts. Will this prevent damage?

I always have my Arduino on 3 volts. Will this prevent damage?

No.