22 Dec
2007
22 Dec
'07
10:58 a.m.
--- Tom Peters <tpeters at mixcom.com> wrote:
At 04:33 AM 12/22/2007 -0800, you wrote:
that
No, you still need the anode resistor. That's a
current limiting resistor. It's purpose is to prevent
too much current from damaging the tubes - you need
that. It's actual value will vary depending on supply
voltage. Since the tubes you have are rather large,
and may draw more current, I'd suggest using at least
a half watt resistor for this purpose. Adjust the
value until you get a good, solid glow from the tubes.
If it looks too bright or has a weird haze, increase
the value of the resistor. If the digit isn't
completely lit, decrease it. Start with the
recommended 1.8k and work from there.
Remember, you don't need any fancy power IC's or DC-DC
converters - you can just rectify line voltage (an
isolation transformer is good if you do this...) and
use a simple voltage doubler circuit (two
electrolytics capable of the voltage, and two 1N4006
diodes). You can get a good 250-300v this way.
-Ian
> > Anyone know a good way to drive these,
four or
six
> of them in an
> > array? I need 170 volts, 21ma all cathodes,
> between 4.0 and 6.0ma
> > any individual cathode. I was thinking of a
pic at
> each tube, sort-
> > of a character generator that would take an
ascii
> code and drive
> > the right segments. Some sort of escape code
would
> let you send 16
> > bits to be interpreted literally, i.e. turn on
the
> literal segments
> > corresponding to the bits set, for more
fanciful
displays.
To actually drive the tubes. you need something can handle the volage/current. Use MPSA42
transistors
- they're cheap, about 8 cents each. One
transistor
per cathode. Tie the anode of the tube to the power
source of 200v or whatever. Connect each cathode to
the collector of a MPSA42, tie the emitters all to
ground. To drive a segment, drive the base high
through a 33k resistor.
Great information, thanks. Someone else suggested
MPSA42's and '92's as
well. The Burroughs spec sheets talk about the
series anode R recommended
for each of three types of tubes; for the B-7971
they say 1.8k. Does your
suggestion eliminate the need for a anode resistor?