I've got a 8-bit shift register 74HC595 connected to 8 opto-isolators.
But before arduino boots, the shift register turns on the opto-isolators in a random state. Also, I have a long 5-wire connection from the arduino to the shift register, so if not absolutely necessary, I would prefer to keep only 5 wires.
Instead of putting another wire for the "enable output" pin, can I just plug the shift register's vcc to an arduino pin? This way it all would be turned off, before arduino boots and I set the "vcc" pin to HIGH.
- Is it OK to power up a shift register by a arduino IO pin?
- Do I need resistors for the IO "power" pin?