piclist 1998\10\07\011346a >
Thread: 4 digit auto-ranging frequency-meter.
www.piclist.com/techref/index.htm?key=digit+auto+ranging
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face BY : Dave VanHorn email (remove spam text)



>>The base resistors arent' critical, 470 ohm or 1k should work.
>
>Do you really think THAT low? Even if the transistors were completely
>saturated, I would expect the base resistors to be about 10 times the
>segment resistors. If we used 470 ohm resistors on the bases, with a
5V
>supply, we would have a base current of about 8mA. It would work
fine, but
>it would seem to me that for efficiency's sake, a few K would be
better. It
>would still throw the  transistors into saturation and save some
power.


You have to allow for all seven segments to be on, plus worstcase of
the pic output drive..
A higher R will probably work. I'd use high eff red displays then, and
do the math. This is an off-the cuff shot.

<000a01bdf1ac$4c2983e0$0200a8c0@xemu> 7bit

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