I'm looking to see if my logic here is correct. I am looking to drive 20 banks of 5 LEDs (100 LEDs in total), each bank will have either all 5 LEDs off or on and wanted to know if I could power these all through a ULN2003 so can use 1 pin on the ULN2003 to turn on all 5.
The plan is to use multiple shift registers (595) in order to give me the 20 pins or so that I will need, then each output on the 595 will connect up to a pin on a ULN2003.
The LEDs I have are 3v 20ma so I know each ULN pin will be looking at potentially 100ma (although I will probably drop the current as don't need the LEDS that bright), so should I be looking at only driving 4 banks of LEDs (20) from each ULN2003 as looks like they can give 500ma, but I take it thats across all PINs?
Anyway hopefully that makes sense and would appreciate any help.
PS: On another note what do people use to draw their schematics as seen lots on here and would like to draw these sorts of thing up as I know a diagram always helps.
Thats good if there is something there that does the job of both, will certainly make life easier.
However is what I suggested still possible? Im not ignoring advice or anything just trying to learn so would be good to know if what I was suggesting will work albeit not the most efficient way?
Yes, ULN2003 (or 2803 for 8 outputs) driven by 74HC595 will work as well.
Can put a PWM signal on the 74HC595 OE/ pin to provide dimming control as well.
analogWrite (Ax, 0); //will be full on, and
analogWrite (Ax, 255); // will be full off
The LEDs I have are 3v 20ma so I know each ULN pin will be looking at potentially 100ma (although I will probably drop the current as don't need the LEDS that bright), so should I be looking at only driving 4 banks of LEDs (20) from each ULN2003 as looks like they can give 500ma, but I take it thats across all PINs?
Your math is about right, you can't drive all 8 outputs with 100 mA each. Edited:Same apply for TPIC6B595. Looks like TPIC6B595 is o'k , 8 channels 150 mA each!
CrossRoads:
Yes, ULN2003 (or 2803 for 8 outputs) driven by 74HC595 will work as well.
Can put a PWM signal on the 74HC595 OE/ pin to provide dimming control as well.
analogWrite (Ax, 0); //will be full on, and
analogWrite (Ax, 255); // will be full off
Output Enable to control it's brightness huh, probably do the same with other ics too using that method, i found this thought fasinating to control the chip.. what if OE is in the state off state? I presume no negative influence? Eg can't bitshift while in a certain state...
If OE/ is high, the outputs go into a high impedance state - that is, act as if the chip is not connected.
You can still shift data into the registers.