Re: 4 digit auto-ranging frequency-meter. by Regulus Berdin .

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