Neon bulb logic elements link?

Tom Jennings wrote: I replied: [matrix drive ideas snipped] I've just looked at the specifications for Chicago Miniature Lamp neon bulbs, and it looks like they don't have anything suitable. The problem is that the specifications for the "maintain" and "breakdown" (start) voltage ranges are too wide, and often there is overlap. So unless you are willing to cherry-pick bulbs that meet tighter specs, 2-D matrix drive doesn't seem practical. For instance, the 4AD and 4AE bulbs do have a nice wide separation between the maximum maintain voltage and minimum breakdown voltage, but the ranges are too wide: rated maintain breakdown current voltage voltage ------- -------- --------- 4AD 0.50 mA 60-80V 105-135V 4AE 0.50 mA 60-80V 120-150V For symmetric drive you need to deal with three voltages (in opposite polarities for X and Y): A - below minimum maintain when applied to both X and Y, within maintain range when applied to just one B - nominal maintain when applied to both X and Y C - above maximum breakdown when applied to both X and Y, within maintain range when applied to just one This results in five inequalies to be satisfied. FOr the 4AD: 2*A < 60 - guarantee turn-off 2*B >= 80 - guarantee maintain 2*C >= 150 - guarantee turn-on A+B > 80 - don't turn off non-selected bulbs B+C < 120 - don't turn on non-selected bulbs Unfortuantely there is no set of numbers for A, B, and C that satisfy all five inequalities. For the asymmetric case, you have six variables, since there are different voltages used for each of three states on X and Y. A+D < 60 B+E >= 80 C+F >= 150 A+E > 80 B+D > 80 B+F < 120 C+E < 120 I haven't tried to find a solution to this. Is there any readily available software (preferrably free) that solves sets of inequalities like this? I also can't find a distributor that stocks the 4AD or 4AE bulbs. The C2A is avaialble for $0.186 each in quantity 5000 from Newark, but the characteristics are even more unsuitable. Eric