So i've got my Arduino nicely interfaced with a 74HC595 shift register, as detailed on the shift-out page. I was even able to connect it to an external power source and have it count up with all 8 LEDs -- Wonderful!
However, for my project I wanted to upgrade some heftier, brighter LEDs, and thought a good substitute for the 74HC595 would be the TPIC9B595.
But for the passed 4 or 5 hours it's been giving me a world of trouble. when i got the first chip connected and interfaced, something horrible went wrong and it was flashing random lights all over the place instead of doing the "hello world" counting routine. After some tinkering i got it to almost work -- but drain 7 on the chip was acting as drain 1, and drain 1 never turned on. Weird.
I replaced the chip with a new one and somehow managed to get the counting routine working. The next step after getting it working while connected to the computer was to get the whole circuit running on battery power like last time. However, when i disconnect the computer cable and plug in a battery to power the two, the shift register won't work.
I even tried keeping the computer plugged in while connecting the battery to see if i could switch them over without shutting off the arduino -- the arduino continues to shiftout data (I connected LEDs directly to the arduino to make sure it was working), but the shift register stops putting out any more data.
Now here's the kicker. All the while i've been powering the shift register with the VIN input/output. When i change from powering the shift register with VIN (4.4ish volts) to the 5volt power line (which read about 4.55 volts), the counter stops counting again, no matter if it's connected to the computer or not.
Now, i have absolutely no explanation for why this is happening, and i need guidance. I've checked all my input/output wiring, the only variable that matter seems to be the power and it's just befuddling!
In short:
TPIC9B595 works when it's powered by my computer, but when i try to take the circuit off of computer power and put it and the shift register onto battery power (Which has the same exact voltage as the computer power as per my voltmeter) the shift register stops changing its outputs, even though the Arduino seems to be sending data. I'm at a loss as to why this happens.
The sketch i'm using is the first example sketch on the Arduino Shift-out page "Hello World"
The only edit i made was changing the latch pin to pin 13 and moving the latch pulse to the end and delaying it by 1 milisecond so i can see it go high.