Greg,
Your circuit works, but there may be a better way to get both electrodes
lit on the neon lamps, one that costs less and doesn't put AC mains
power in your circuit boards.
It's possible to use a standard NPN transistor with a pullup resistor to
+90VDC to turn the neon bulb on and off. It's also possible to put such
a circuit on both ends of the neon bulb and drive the two transistors
with combinations of binary 00, 01, or 10 to allow you to alternate the
glowing electrode at whatever rate you like. You can increase the duty
cycle to 100% using this method to get a brighter display.
The transistors can be TI SN75468 chips or similar to save wiring
effort. They also make SIP resistor networks to consolidate the pullup
resistors.
On 2/15/15 12:23 AM, gregebert wrote:
I attached a jpg of my neon-bulb driver, but it wont be much help
because it's just a way to drive neon-bulbs from a CMOS/TTL level. Note
that I use an opto-triac; this is for isolation as well as for AC
operation. Operating a neon bulb with DC only illuminates 1 electrode
(the cathode), rather than both. Ignore the diode; it's not applicable
for your circuit. Funny thing is, I had considered using regular triacs
(not isolated), and keeping the digital circuitry on the AC line, but
the discrete triacs were larger and more expensive than the opto-triacs.
--
David Forbes, Tucson AZ
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