Hi Dennis,

In the past I've shared keyboards and LCDs (never in quite as clever a
way). I found that the diode drops and resistances make it marginal
when you have pullup resistors. Using pulldown resistors, swapping the
diodes end-for-end and changing the code to suit makes for a more
reliable system. The input logic thresholds work more to your
advantage that way, since 1.2 volts is about the threshold.

Cheerful regards,

Bob


On 26 Mar 2003 at 2:40, Dennis Crawley wrote:

> Bob Blick
> > I looked at the schematic and description and it looks to me like it will
> > work, however I would suggest the addition of 4 resistors (one in series
> > with each keyboard row)
>
> Hi, Bob
>
> I have done what you've suggested. If the row resistance grow beyond
> 220ohms, no current sinks through the low-out so the weak pull up remains
> with a logic 1...
> The keypad already has almost 90ohms and the diodes drop some tension.
> Besides, we can add a 330omhs or more in series with LCD data lines.
> It was tested with this configuration and works fine, but some calculations
> must be done to prevent what you have said.
>
>
> Regards,
> Dennis.
>
> Ps:
> I didn't care about it because I was focused on relocatable code. I did it!
> But it gonna take extra time to make that blocks of code a useful thing. I
> fought against a message on Value column "Out of Scope"... and the
> temptation was "ok, back to absolute!", but the spirit of Olin showed off
> anD told me: "You will never understand this,... but you can try". So, now
> I have the relocatable workable version of the lcd-keypad...
> (RTFM+TRY$ERROR+COFFE,a lot of coffe). 8p

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