No. Think about a given pattern you may want to display that turns on all 16 leds of a single level (Row) going to a single output pin driving that row. That could be 16 X 20 milliamos of current which is more then the poor row enable pin can supply, hence the need to use 4 switching transistors to drive the 4 levels (Row). That make sense? Regardless, I am amidst some heady (for me) reading on transistors and hope to understand the use of them for this project if necessary. I have some 2N2222's here and was initially planning on using these on the rows but am having some serious trouble understanding the calculations behind choosing correct resistors to use with the transistors. Any "beginner language" help would be greatly appreciated.A 2N2222A transistor is really not able to switch 16 x 20ma of current, you need a 'bigger' transistor.
I built an indicator out of various 3mm colored LEDs. The red, green, yellow, and blue LEDs were all diffused, but the white was clear. I sanded it with a fine sandpaper and it turned out great. Easy does it though, a little goes a long way. I canned my first attempt because I had sanded several flat spots into it. ;-) (Technically, I didn't can it, I just use it for breadboard projects where I don't care about the visual quality. Why waste a good LED?)At the risk of being a FET pusher, try a small MOSFET instead. This is the perfect sort of application for them. You should use a small (100-200R will do fine) resistor for good measure, but the FET gate (analogous to the base of a BJT) has a high impedance, so there's no need to current limit or calculate gains. You'll need a logic level FET.I use VN10LPs for moderate current (270mA) -- here's a link to Digikey: http://www.digikey.com/product-detail/en/VN10LP/VN10LP-ND/92610If you're driving them all at a full 20mA, you'll need something with more gusto. Here's a ZVN4206A good for 600mA: http://www.digikey.com/product-detail/en/ZVN4206A/ZVN4206A-ND/92604Those are both N-channel, so you'll be switching between the LED and ground. (Same as NPN.)
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