AVR-Chat

You all have given me a bunch of valid options - thank you.  I think
the best fit for my application will be the 8-to-3 priority encoder. 
It's not too expensive and it works down to 2 volts.

Richard Cooke

--- In AVR-Chat@yahoogroups.com, Samir Lohani <slohani90182@...> wrote:
>
> > 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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