If you want to make this rock-solid, the pulldown resistor can be calculated knowing the max tristate leakage current (usually 10uA) and ensuring that 10uA of leakage does not produce enough base-current to turn on the transistor.
Worst-case, you will have a transistor with infinite current-gain (beta). Then the problem is to prevent voltage at the base to start turning on (0.7V). That works out to 70K. This is approximate, because there is additional leakage current at the transistor itself (collector-base leakage), which is typically much less than 1uA. This is just a quick-and-dirty calculation and in a real circuit the pulldown resistor will have a higher value; if you factor-in transistor beta (lets pick 100) and take a swag at how much current is required before the nixie starts to glow (my experiments with b7971 tubes show 100-150uA is needed), an emitter resistor of about 1.5K, the pulldown resistor works out to 94K, which is pretty close to the quick-and-dirty value. -- 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/047cd617-1d3f-415b-bf97-a0244f1a0e09%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
