I'm looking for a transistor array IC with a common base to all the transistors, but I'm having some trouble finding what I'm looking for. Essentially, what I want is to take 8 data lines in parallel and be able to (somewhat rapidly) switch them on and off - that is, for 8 lines, switch all of them on and all of them off with one input line. I can do this with 8 individual transistors, splitting the input line itself into 8 parallel bases, but I'm hoping some actual EE out there - i.e., not a dabbler like me - knows of a nice little chip that will do the trick and save me some soldering.
You can imagine what it's like trying to search for "transistor integrated circuit", but that's what I want - an IC with 8 NPN transistors, all of which take their base off of one pin.
I'm attempting to drive quite a few 14 segment dual digit LED displays (like this one - the internal circuit diagram is important to this issue) with a fancy little LED display driver here (details less important. Fancy 16 bit shift register.) The LED driver has some nice features that would be annoying to duplicate, like individually-controllable PWM dimming for each segment, and this would be just fine with a seven segment LCD without multiplexing. Shift in the bits, latch it up, and we're good.
Unfortunately, the 14 segment LCD's only seem to work through multiplexing, as you have 8 input pins that are multiplexed among 4 different "regions" by choosing the anode. You can't just latch the bits you want on the driver and forget it - you need to control the bits as a combination of anodes and cathodes.
What I'm thinking of now is to drive a closed loop shift register with e.g.
0001 in a loop and choose the 8 cathode inputs by
and-ing or switching them 8 at a time out of 32 latched input lines (that is, 2 of the driver chips, but only 8 bits of those chips at any one time). This way I would be able to shift the desired bits into the registers and ignore the whole circuit from the microprocessor's point of view (minus the shift merry-go-round clock pulse, which is minor). Just let it round-robin multiplex itself until I want to come back and display something else.