On 7/2/10 7:03 PM, msilv3r wrote:
C - HV PSU -> collector
B - PIC output -> resistor -> base
E - emitter -> resistor -> anode of nixie tube
Now I think this would work. However, I then looked at some of the nixie
tube designs in the Files section. What do you know, he used the MPSA42 also.
So I've got some validity to that decision. However I noticed oz2cpu used
two resistors for each set of on/off switches. I don't quite understand
why. I would guess perhaps to protect the PIC I/O pins from any
faults/leaking current. I know transistors somewhat, but not as much as
I will after next semester. There is a lot I don't know, and this is a
good example. Could someone please explain this to me. Thanks.
Also, whats with the 100n capacitor on the VCC/GNDs?
-Mike
Mike,
The reason to use two transistors is that you need a level translator to isolate the PIC output at 0-5V from the anode of the nixie tube which sees up to 180V. Otherwise you'll find that you either can't turn on the anode or that you can't turn it off or that your PIC blows out.
The standard approach used in most nixie clocks is an NPN transistor driven by the PIC whose collector controls the base of a PNP transistor that gates the tube anode.
Here's my circuit:
You can use an MPSA42 for the NPN and an MPSA92 for the PNP; they cost less than the Zetex transistors I used.
I recommend the resistor values in the above schematic, as it worked flawlessly for me. Others have had good luck with different values.
--
David Forbes, Tucson AZ
