I'm working on making a clock (or something) out of some VFD tubes that I got from an old calculator. I've figured out how to make a tube work. The filament get 1.2v, the grid and segments get 12v. Now I want to use a decoder to drive the segments off of a counter. I've got a couple SN74LS47 chips that look like they can do the job. I can figure out how to get the inputs, my confusion is how to get the 12 volts.
I've attached a little schematic, the chip gets 5v, then the 12v is from another supply and needs to get turned on to light the segment. I think that would be called a pull up resistor, but what value should it be?
BTW, the rules of this project require that all (or most) parts come from my boxes of ttl chips, no micro controllers allowed. Thanks for your help.
I've attached a little schematic, the chip gets 5v, then the 12v is from another supply and needs to get turned on to light the segment. I think that would be called a pull up resistor, but what value should it be?
BTW, the rules of this project require that all (or most) parts come from my boxes of ttl chips, no micro controllers allowed. Thanks for your help.
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