I'd get rid of the 1Ks, and go directly. They are powered, from the same 5V supply ? Unterminated TTL inputs float to ~1.6V, look like an "iffy" logic-1. To drag them down to solid logic-0 (0.8V min) requires a "sink" current of 1.6mA for old standard TTL. A 1K is too big. Unused TTL inputs are almost always terminated high, as the "source" current to a good logic-1 (>2.0V) is much smaller than the sink current. To terminate original TTL low, would require a resistor ~220 ohms.
On Wednesday, January 24, 2018 at 2:26:19 PM UTC-8, Jonathan wrote: > > Hi All, > > I am finally getting around to soldering up a pixie tube thermometer > that I bread boarded quite a while back. It uses a PIC and two > SN7414N's. On the bread board I have 1k resistors in series from the > output pins of the PIC to the input pins of the SN74141Ns. Usually I am > using shift registers but with a two digit thermometer I am coming > directly off of the PIC pins. I can't seem to remember why I put the > series resistors in there. Are they required? > > Forgetfully yours, > > Jonathan > > -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to neonixie-l+unsubscr...@googlegroups.com. To post to this group, send an email to neonixie-l@googlegroups.com. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/8e4644c2-7fe6-4c82-84a1-ec2c990d3456%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
