hi all!
I soldered the diodes in and assumed the dark band on the diodes meant ‘-’. and soldered the board on . and soldered the switch on…but it doesn’t seem to be reading keypresses. I’ve followed all the directions. loaded the arduino ide. made the led blink. but i’m wondering how to tell if i soldered the diodes wrong or something else. i just don’t know how to tell what i did wrong.
Hi Lesley.
It looks like you’ve put the diodes where optional LEDs go. Since the LED pads are not connected to anything it’s safe to leave them there but you’re going to need to get some more diodes and populate them in the correct places on the board. If you look beside each switch there’s a spot for a rectangular component with a line on one side of it. That’s where you need to put the diodes and the black band goes on the side that has the line on it. (see photo)
I’d recommend not trying to desolder the diodes you have now unless you have the tools and skill to get them out. (Even then you could overheat them and cause damage.) It would be a lot easier for you to just to get 14 more diodes part number [COM-08588 and solder them in place beside the switches. 
The diodes are just intended to prevent “ghost keys” (ref: https://github.com/nickgammon/Keypad_Matrix).
If you bridge a wire across where each diode is supposed to go, the keys will work. However, with wires instead of diodes, pressing 3 keys in a square pattern at the same time will result in an extra “ghost” key press. So for example if you press top/left, bottom/left, and top/right at the same time, the bottom/right key would also act as if it is pressed (ghost key!).
