Olin Lathrop wrote:
> Jinx wrote:
>   
>>> Why can't the PIC run from the 3V supply too ?
>>>       
>> IMHO 3V is just too low for that circuit. If the high- and low-side
>> drivers each drop a volt (the 2003 at least has Darlington outputs),
>> after the current-limiting resistor that leaves crumbs for the LEDs.
>> And the LEDs are an important part of this project
>>     
>
> I agree the LEDs need a reliable higher voltage, which is why I suggested to
> use a step up converter for the LED supply.
>
> Since most of the battery power will go into LEDs, I also think the LED
> drive circuit should be designed for efficiency.  Dropping a volt in either
> high or low side drivers is way too much, and totally unnecessary.  Off the
> shelf darlington drivers are definitely not the way to go in this case.
>
>
> ********************************************************************
> Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
> (978) 742-9014.  Gold level PIC consultants since 2000.
>   
Please correct me id I am wrong, but, with a 5v supply for the LED's, 
won't most of the battery power be going to the current limiting 
resistors rather than the LED's (with 3.3V drop over the resistor, but 
1.7 of the (red) LED. OK, there's also the 1V drop in the drivers or 
something too.... but, the point is that with only 1.7V drop on the LED, 
the other 3.3V drop is the bulk of where your battery power goes... (2/3 
of your battery power goes to everything other than the LED's).

My 'novice' instinct is to boost the power to as low a value as possible 
to drive the LED's thus keeping the device more efficient....

Rolf

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