[time-nuts] Follow-up question re: microcontroller families
hmurray at megapathdsl.net
Sun May 26 20:17:46 EDT 2013
bownes at gmail.com said:
> For making a blinking LEDs, it is hard to beat a 74LS74. However, a PIC, is
> probably less expensive! :)
I was going to send a wise-ass comment, but then I checked some numbers.
Digikey, one-off DIP pricing:
So technically you are correct, but only because you are picked an ancient
Besides, the '74 needs a clock while the PIC has an internal clock calibrated
I suspect what's going on is that the '74 is pad limited(*) so you are paying
per-pad rather than per gate. The PIC only has 8 pins, so if it's close to
pad limited it will be cheaper.
The PIC10F200 has 3 output pins so it can blink 3 LEDs independently while
the '74 only has 2 FFs.
High volume (whole tape, 2-3K) prices are $0.34, 0.22, and 0.10
*) If you aren't familiar with pad-limited, it's a cool idea. Consider a
chip that has N pins. Each pin needs a pad for the bond wire. Arrange those
in a rectangle around the perimeter of your chip. That leaves a hole in the
middle. Put your logic in there. If it doesn't fit, push the pads out until
there is room. That makes your chip bigger and more expensive. If it fits
with room leftover, you can add more logic for free. That's why low cost
watches have so many features.
These are my opinions. I hate spam.
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