Thanks, I will try it but I am currently renovating my whole apartment,
including my hobby room, so that will be many months into the future but it
is on my list - maybe I can't keep from checking it before I have finished
renovating, you know how it is when your fingers itch to do something
A lower voltage on the base would work, or an extra diode in series with
the EMITTER to raise the turnon voltage by another 0.6V, or just pullup
resistors on the chip outputs to make sure they go to a righteous 5V.
Remember you still need those emitter resistors, otherwise the B-E diode
will
Yes, it should work perfectly in that application with a CMOS gate. I would
not try it with a TTL gate though, as it relies on the output going to the
5V rail to turn the transistor off and bipolar can't get up there. To use
TTL you would need to add pullup resistors to 5V on the gate outputs.
Pete, will the cascode circuit work properly as a cathode driver if you use
for instance a 74HCT42 or a 74HCT138 to drive the transistor (they both
have inverted outputs going low when selected), using the collector of the
transistor to drive the cathode of a Nixie?
/Martin
--
You received
Thanks Pete -- my design uses the SMT versions of the transistors so I'm
particularly interested in reducing the power dissipation. Please clarify
the placement of the helper resistor -- in the vertical leg of the Q1
collector circuit, or in the horizontal leg of the Q2 base connection?
If I
With the conventional circuit, you have two saturated transistor switches,
each of which needs to turn off to blank the anode. Each may take a few
microseconds, and the second stage doesn't start its time delay until the
first stage turn off is completely finished. With most designs the
Hi Pete,
I like it. I will give this a try.
-joe
On Thu, Feb 26, 2015 at 3:12 AM, petehand peteh...@gmail.com wrote:
One more thing about the cascode. Transistor Q1 is dissipating 170mW with
the values shown. It may get a little warm - you have to watch that. You
can put a helper resistor
Pete, that's a nice application for the cascode circuit... Help me
understand how it eliminates concerns about dead time and ghosting.
Terry
On Thursday, February 26, 2015 at 3:05:55 AM UTC-6, petehand wrote:
One more thing about the cascode. Transistor Q1 is dissipating 170mW with
the values shown. It may get a little warm - you have to watch that. You
can put a helper resistor between Q1 collector and Q2 base. The value is
completely immaterial since the current is set by the R2 emitter resistor,
https://lh5.googleusercontent.com/-_PML27wwc9w/VO7hHsuYRwI/ATA/LVcwCOp5mWw/s1600/IN17.jpg
I did mean to change R22 to 10k, but I can suggest an even better way. This
is a circuit I've used to multiplex IN17s, with no dead period and no
ghosting. It looks terrifyingly unsafe. Let me
Perhaps you can post the code that does the multiplexing - it may shed some
light on this issue. By the way, there's nothing wrong with multiplexing -
and it's not that hard to get it right, just follow a few simple rules like
the dead time, and you also haven't mentioned the frequency yet,
Just move R22 etc to the other end of R21 etc, on the base of the PNPs.
Where they are now, those resistors are are doing nothing but wasting
power. When the NPNs turn on they're going to draw 1.6mA and drop 160V
across the 100k resistors R21 etc. You need no more than 3V to turn on the
PNPs,
I used direct-drive on my first nixie project only because my gut-instinct
was to keep it as simple as possible; I've stuck with that ever since.
Too many postings about 'noisy nixies', choosing the correct
cathode-current, bleeding, flickering, RFI, etc. I've even seen
scary-looking blue arcs
Hi Yall,
I've attached a picture of the display pcb layout and a pdf of the
schematic for it. The cathode drivers are just the MPSA42 with a 100K ohm
base transistor and the collector is tied directly to the cathode and the
emitter is tied to ground.
-joe
On Mon, Feb 23, 2015 at 10:58 AM,
Joe -- the anode driver I borrowed from the open-source clock looks
slightly different than yours.
It uses the same transistors, but the MPSA92 has 100K directly across the
BE junction, and a 470K between the MPSA42 collector and the MPSA92 base.
In other words, imagine moving your R22 to
Does the issue happen more to certain tubes/digits than to others? If so,
it could have something to do with the layout of the traces: i'd be
especially worried about long runs of high voltage lines parallel to the
lines switching the transistors. E.g., in your PCB, the trace at the very
Greg,
I concur that these are fine things to do. I adjsuted my base-emitter resistor
so that it would have about 0.3V across it if the base were disconencted form
the circuit and the driving signal was on.
Also, short wires from the driver to the tubes are helpful to reducing
crosstalk. I
Hi Yall,
Okay, I scoped the board and I have almost 500us of total dead time between
digits. This was measured on the digital outputs from the CPU. My code is
written in a way that I turn off all of the segment and digit signals one
at a time in a for loop so they are not all triggering at once.
Greg -- regarding the resistor size and power dissipation, if there are 6
digits (7 in this case with the neons), can't you figure the resistor duty
cycle is 1/6th, and therefore smaller wattage resistors can be used? The
average dissipation is more like .043 watts, by my back-of-the-napkin
Hi Yall,
Thanks for the inputs, Sadly direct drive is not an option, I just don't
have the I/O pins available nor the space to add the chips needed to
'produce' more.
Terry,
By other pin, I mean the side considered the anode side of the neon bulb.
The side that is positive when the bulb should
Interesting. Can you take some pictures of the problem? And maybe provide
the schematic? (at least of the part driving the nixies).
On Monday, February 23, 2015 at 1:15:08 PM UTC+1, joenixie wrote:
Hi Yall,
Thanks for the inputs, Sadly direct drive is not an option, I just don't
have the
I will try the biasing. would biasing both sides help? This would be sort
of like terminating the lines.
No need to worry about termination at this frequency, as in reflected
waves, unless your PCB traces are several feet long...
I did check the datasheets for the MPSA42/MPSA92 and they
Actually you need to be careful with planes -- they can actually couple the
signal from one switching line to the next. You may have better results
minimizing parallelism between traces, lengths that is, and maximizing
spacing between those traces.
Slowing down the edges, using termination if
Joe, what do you mean by other pin?
Terry
On Sunday, February 22, 2015 at 10:17:23 AM UTC-6, joenixie wrote:
Hi Yall,
I am working on a multiplexed display and am finding that for the lines
that have both of their transistors turned off, there are massive swings of
voltage that are
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