AVR-Chat

--- In AVR-Chat@yahoogroups.com, "kc9dag" <dpboyer@d...> wrote:
> 
> I would like to interface my Butterfly to a PS/2 keyboard and I 
have 
> a question:
>    The Application note on interfacing to a PC keyboard says that 
one 
> of the lines is the +5v line... the Butterfly (mainly it's 
dataflash 
> which I AM using) can't go up to +5v.  Will the keyboard work on 
+3v, 
> or can I power the keyboard from a +5v source and just use a common 
> ground between the keyboard and the butterfly (and if I do it that 
> way, can the AVR's inputs handle the +5v while it is running at 
> +3v)???
> 
> Thanks,
> Daniel

"can the AVR's inputs handle the +5v while it is running at +3v"

While I have not tried it to confirm, I say NO.

A 3VDC supply (2 AA batteries) and 5VDC supply (3 AA batteries) with 
the negative tied together should work.

For the DATA leads going back to the Butterfly do this
In Series: KYBD (2000 ohm resistor) BFly (3000 ohm resistor) Common

The signal comes out of the KYBD at 5VDC, 2V is dropped across the 
2000 ohm resistor leaving 3V across the 3000 ohm resistor for the 
BFly. You can probably see the ratio I'm using 
5000 = 2000 + 3000 (1.8K and 2.7K would work just fine). It could 
just as easily be 
10000 = 4000 + 6000. Just make sure that the total resister value is 
going to be high enough that the output of the keybaord is not loaded 
down. Here a higher resistance is better.