> I am using a PIC16C84 to drive some 7 segment LED displays.  My problem
> is that the LED's are those BIG (3 inch) ones and each segment needs
> 40mA.  I was going to use a 2803 to drive them but with all 7 segments
> on, it looks like the power was too high.

> Can some of you suggest the best (simplest/cheapest) way to drive these
> LED's.

You could use multiple ULN2803's or ULN2003's, keeping the package
dissipation within bounds on each;  (ie: Don't use all channels per pkg).
They're cheap.  {For any reader who is unfamiliar, there are 8/7 channel
DIP packaged darlington low side drivers.)  This may be closest to your
current design (no pun intended) and thereby simple in that way; also
cheap.

You could consider the the MAX7219, which will handle everything for up
to 8 zeven-segment-plus-decimal LED displays.  It has high side drivers,
low side drivers, BCD-7 segment decoders, oscillator, current limiters,
RAM for the BCD, intensity modulation via PWM, shift register input
(fewer pins).  Around $8 in small quantities, US.  I believe that
Harris/Intersil have a similar parallel interfaced chip in the ICL7218.
Being N-way multiplexed (for N digits), this may be less bright than you
wish, tho you can probably up the peak current some to compensate.  This
may be the simplest, in that one chip and a single current setting resistor
handles up to 8 digits; you don't even need current limit resistors per
segment.  (You can also use the MAX7219 in direct undecoded mode, with
individual control of each segment).  Check the Maxim web pages.

Or you could substitute the TI TPIC6B595 8 bit SIPO latched shift register
with low side drivers; I think these can handle your 40ma / segement
continuous current, unlike the ULN2803.  Again, fewer pins needed, but
you need to handle multiplexing the high side, or use one per digit
unmultiplexed.  This is back to your earlier design, but with a shift
register/latch with more drive.  Check the Texas Instruments web pages.
    Zhahai

@ Zhahai Stewart       zhahai@hisys.com
@ A Meme Gardener      http://rainbow.rmii.com/~hisys/zhahai.html
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