piclist 1998\10\07\051425a
>
Thread:
4 digit auto-ranging frequency-meter.
www.piclist.com/techref/index.htm?key=digit+auto+ranging
BY
:
Regulus Berdin email (remove spam text)
Dave VanHorn wrote:
>
> >You can still minimize the parts by having the 7segment common anode,
> >make all the colllectors of the NPN transistors tie to the +5V supply
> >and reverse/invert drive to the LED (to the negative side). This way
> >the base resistors is not needed anymore.
> >
> >Reggie
>
> Are you SURE they will turn off? Look at the pin specs for minimum
> high output voltage, and leakage current. I've got my doubts about the
> current design, but IIRC, they can drive closer to ground than to VCC.
Yes I'm sure, 25 ma for sinking, V(OL) = 0.6V . I had used this
configuration on some of my designs.
In case you misunderstood my point, here is an ascii schematic of what I
meant.
O Vdd
|
O---------------O---------------O---------------O
| | | |
| | | |
|/ |/ |/ |/
RA0 O---B| RA1 O---B| RA2 O---B| RA2 O---B|
|\ |\ |\ |\
V V V V
| | | |
O O O O
digit select 1 digit select 2 digit select 3 digit select 4
RB1 O---/\/\/\-----O Segment A
RB2 O---/\/\/\-----O Segment B
RB3 O---/\/\/\-----O Segment C
RB4 O---/\/\/\-----O Segment D
RB5 O---/\/\/\-----O Segment E
RB6 O---/\/\/\-----O Segment F
RB7 O---/\/\/\-----O Segment G
Reggie
<361B2271.339D259B@skyinet.net> 7bit
See also: www.piclist.com/techref/index.htm?key=digit+auto+ranging
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