cmosdigital-logicttl
I've been looking for a 3.3V compatible shift register (SIPO) with latched open-drain outputs. I've settled on a 74xx596 (not a '595!), but of all the 74xx CMOS series I've been looking at omit this one. Any idea on why? and if it's possible to get CMOS variants of these, because of the open-drain outputs?
Correction: I was getting confused between 595 and 596. 595 has tri-state outputs, 596 has open collector outputs.
The 74LCX07 will not clamp the output to \$V_{DD}\$ (the datasheet talks about \$V_{CC}\$), since its particularly targeted at interfacing between different supply voltages. Note that the inputs are 5V tolerant, also with \$V_{DD}\$ = 3.3V.
The datasheet says maximum output voltage is 5.5V (never use the 7V mentioned under Absolute Maximum Ratings), but should have mentioned for what supply voltage, for instance also for 3.3V.
The only characteristic I could find which actually indicates that a higher output voltage is allowed is off state current on page 4, which gives a value of 10\$\mu\$A at \$V_{CC}\$ = 2 to 5.5V and \$V_O\$ = 5.5V.
edit
That could have been clearer. Especially since it contradicts what it says under Absolute Maximum Ratings: "DC Output Diode Current, for \$V_O > V_{CC}\$: 50mA."
The NXP 74LVC1G07 seems to be a solution.
To level shift up from a 3.3V system to drive 5V CMOS input levels, simply connect the LVC output to a 5V termination voltage through a pullup resistor as shown below. The outputs of these devices are 5V tolerant and provide a simple solution to drive 5V CMOS input levels.
From here.
It also only mentions output clamping current for \$V_O < 0\$, so it won't clamp 5V.
You should really use (timer) interrupt driven firmware to ensure your clock ticks accurately. Software delays will cause a gradual drift because of variations in your program flow. Here is a good overview of how to use Timers on the Arduino platform. You can follow something like the pattern described in the section on "Blinking LED with timer overflow interrupt". The Arduino's 16MHz crystal is plenty accurate for a toy clock project if you write the software correctly.
This style of writing software is "event-driven," so you have to get your mind around that first. The hardware tells you something happened (in this case a second has passed) and your software reacts to it. Instead of you telling your software to "wait a second" and then doing something.
Best Answer
I'm playing around with TI's TLC5925, which is functionally very similar to what you're asking for. It is designed for driving LED's at a constant current, and the logic is 3.3/5V CMOS. The output is tolerant of up to 17V, although I don't know how well it would drive the outputs to logic levels. Not sure if this is suitable - just taking a wild guess at your intended application.