Hey I am doing the shiftOut tutorial with 16 LEDs (Example 2 on this page: http://arduino.cc/en/tutorial/ShiftOut), but both LEDs connected to Q0, aka the first LEDs in each set, are much dimmer than the others, even when they're the only ones lit. Any ideas?
I assume you used the correct resistors and they are all the same?
Try swapping LEDs and see what happens.
Not all LEDs are the same.
Make sure you only have 0.1uF cap from pin 16 to Gnd. No caps on control lines, that is bad for the Arduino outputs.
74HC595 is not really rated for this application.
Assume 220 ohm resistor, and Vf on LEDs of 2.2V (typical for Red).
Then current flow is:
(5V - 2.2V)/220 = 12.7mA
With 8 outputs on, that's 101.8mA. Vcc pin is only rated to 70mA Absolute Max.
When the Vcc internal bond wire goes, the device is dead.
Make some voltage & current measuements, see what you are getting.
steinie44:
I assume you used the correct resistors and they are all the same?
Try swapping LEDs and see what happens.
Not all LEDs are the same.
Resistors are the same, switching LEDs does nothing, it's the current being sent to Q0 that's an issue. I placed a lower value resistor and it's marginally brighter but still not like the rest.
CrossRoads:
Make sure you only have 0.1uF cap from pin 16 to Gnd. No caps on control lines, that is bad for the Arduino outputs.
Where do I put the capacitor? Pin 16 goes to Vcc
Also I modified the code so only 4 are lit at a time (with multiplexing) so it shouldn't be an issue.
Where do I put the capacitor? Pin 16 goes to Vcc
Yes you put it between Vcc and ground not the latch pin as shown in the tutorial.
Also I modified the code so only 4 are lit at a time (with multiplexing) so it shouldn't be an issue.
Yes it will, multiplexing makes the LEDs dimmer.
So you use 2 capacitors?
One is good, but 2 is better. Between pin 8 and 16 of each 74HC595.