AVR-Chat

> I need to read an 8 switch dip switch but I only
> have 3 inputs left. 
> I'm using 2 AAA batteries for this project so I
> need to use low voltage/low power parts.
> Anybody have any good ideas?

You can use several approaches:
1) Diode matrix with pull up resistors as a 8 to 3
decoder. Use schottky diodes to keep VL within 0.3V.
2) If ADC lines are available, use a resistor network
to sense several keys from one line while keeping a
respectable noise margin. Will also detect multiple
key presses.
3) I2C or SPI ICs (see maxim site) which have a
working range of 2.5 - 5.5V.
4) If some of the output lines could briefly be
switched without disturbing the circuit (say while the
ENABLE signal is unasserted as in the case of LCD
bus), connect those lines via a (schottky) diode and
the switches to a common input line. The input line
should be pulled to inactive state when the switches
are OFF by a suitable resistor.
5) Are 8 switches *really* required? Will combinations
of switches or a menu based approach not work? Will a
BCD switch work?

Cheers,
Samir.


       
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