--- In Electronics_101@..., "ghidera2000"
<ghidera2000@y...> wrote:
--- In Electronics_101@..., "upand_at_them"
<upand_at_them@y...> wrote:
I want to use a Multimedia Card (3.3V, SPI) in a circuit that's
mostly 5V. Is there a simple IC that does the level shifting?
Mike
I was just playing with that sort of thing. Couple possibilities:
Simple way: Run your 5v signal through a resistor and a 3.3 zener
diode to ground. Go from the zener to your 3.3 device. Resistor size
depends on the current requirements of your 3.3 device. If its just
communications then a 10k resistor should be fine.
The slightly more complicated method was to use a 74hc245/244
powered from the 3.3 volt side. Your 5v inputs to it need to run
through some honkin' resistors (like 1 meg) though. The 244 will
latch up to 5v and push your whole 3.3 circuit to 5v if you dont
massively limit the current on the 5v side.
Seeing the 74hct4245 link in the previous message though, I'd say
forget the 245 - much safer with the other chip or the diode method.
The problem with using resistors on signal lines is speed. The inputs
and the traces are largly capacitive so added resistance on digital
signal lines slows down the rise and fall times dramatically.
