the obvious next step from my led clock was
of course, a nixie clock. i became quite enraptured with the idea of
designing and building my own nixie clock once i realized what nixie
tubes were, so i bought some IN-8 (ИН-8) nixie tubes from
ebay and went to work on a clock design.
at first, my design was crude. using eagle, i put together a clock
which used cd4016 decade counters, mpsa42 cathode drivers, and an avr,
as well as an integrated boost controller. my mistakes were numerous,
and they resulted in the frying of an atmega8535 and an stk500. :/
my second design used a max1771 boost converter and an avr which drove
six 74141 nixie drivers through sn74hc595 shift registers. this design
was too expensive to even try, so i scrapped it. (i used an autorouter
to route the traces on the board anyways, so it's a good thing it never
went anywhere... never trust the autorouter! :P)
the nixer mainboard:
finally, i decided to rectify the (120vac) mains to 170vdc for the tube
voltage and use a multiplexed setup: ten mpsa42 cathode drivers and six
mpsa92+mpsa42 anode drivers. the atmega16 receives a pulse-per-second
interrupt by prescaling the signal from a 32.768khz watch crystal. a
second timer/counter is used to multiplex the nixie tubes at 31.25khz.
of course, there are switches to increment the hour and minute.
nixer mainboard pics:
here are the designs for the main controller board of nixer:
the code for nixer is C linked against the avr-libc open-source library
for avr micros. avrdude commands are already available through the
makefile included. the gerber zipfile is ready for sending to batchpcb,
if you were interested.
testing the driver circuitry with the 170vdc from the wall, while it
proved the driver circuits worked, fried a few switches and diodes along
the way... so, as a quick fix to ensure the safe operation of the device
for years to come (and in other countries) i designed a simple
attiny13a-controlled boost converter to step up 12vdc from a wall-wort
into the 170vdc required by the IN-8.
the avr (attiny13a) runs a simple C program that monitors the voltage
at the output of a resistor-divider and adjusts the duty cycle of its
internal 31.25khz pulse-width modulation peripheral. the RAM size of
the attiny13a is a tiny (pun?) 1kB, so no fancy PID controls here.
boost converter pics:
here are the designs for the power supply board of nixer:
