Re: LCD controlling with comparators

From: Danny T (danny_at_nospam.oops)
Date: 01/16/05 

Date: Sun, 16 Jan 2005 15:54:50 +0000

Anthony Fremont wrote:

> I always wanted to put a pic, a lithium battery, a hall sensor (or MEMS
> accelerometer to be really cool) and a column of LEDs into a pendulum
> bob. Then the swinging column of LEDs could strobe out the date/time in
> a format suitable for people that have problems with analog dials and
> hands. ;-) I really have to get this done.

Sounds like fun! Just make sure you're not posessed to get Blue LEDs...
Can we say tacky? :-)

> Yes, you would pick your resistor size so that enough current could be
> supplied to the device being switched on and off.

I believe one resistor would do all the pins.. I'm not sure how that
would work though, given I'd end up with different currents depending on
how many pins where high/low!

> You can do it either way you prefer. Many CMOS parts are better at
> sinking current than sourcing it, but the PICs have the same limit
> either way (usually 25mA per pin)
>
> When the PIC is outputing a 0, then it is actively driving the pin low
> and can sink current. When it is outputing a 1, it is actively driving
> the pin high (except RA4) and can source current. If you hook two PICs
> together and try to have a dualing outputs contest, one of the pins will
> not survive. Always use a current limiting resistor between pins that
> might try to do this.

Do you mean having the output of a pic fed to the input of another? Like
I need for my clock? Should I put resistors between them?

Oh, and each output from my "driver" is connected to 4 inputs (one from
each of the other pics) - anything I should be careful of there - 4
inputs probably draw 4 times as much current - is there a problem here? 

-- 
Danny

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