It was my experience and learning from this list that originally inspired the research in that IN-9 document. Based on some private correspondence, Jan asked me to write something for his site, hence the doc.
I believe John's suggestion of an MPSA42 configured as common-base amplifier will work. I've used a similar common-base circuit with 7400 TTL outputs, which are current-sinking as well. I would add the following additions to John's recommendation (unverified): 1) Consider placing R1 (in John's schematic) between the MPSA42 emitter and the TLC5940 output instead of between the IN-9 and B+. This will limit base current regardless of what the TLC5940 driver tries to do (says person who has blown more than a few MPSA42s by somehow putting base @ 5V and emitter @ GND). 2) The TLC5940's PWM feature will probably not work. PWM of LEDs is "integrated" by the eye to see intensity modulation... while the IN-9 needs true current modulation. Assuming the driver circuit can switch fast enough, PWM would likely just intensity modulate an unchanging bar length on the IN-9. However, it looks like the TLC5940's "dot correction" feature is exactly current modulation of the individual outputs. The big caveat is that it is only 6-bit vs. 12-bit for the PWM (64 instead of 4096 steps). If you can live with only 64-steps in your spectrum analyzer (I probably could), that may not be a big deal. 3) A proposed design approach: - Choose IREF so that the max output current from the TLC5940 is 10mA, the full scale value for the IN-9. This looks like a reference resistor (R-IREF) of about ~3.9k, based Figure 3. - Choose R1, to be placed between MPSA42 emitter and TLC5940 output so that the TLC5940 output voltage will be about ~2.5V (arbitrarily chosen to be the center of the supposed 5V power supply) -> (5V - 0.7V - 2.5V) / 10mA -> 180ohm. This would basically be Figure C from my IN-9 doc, with R1 = 180ohms, Vin hardwired to 5V, but with the TLC5940 connected in place of a fixed GND. - To control, set all TLC5940 channels to 100% PWM, but dynamically set the dot correction (DCx) on each channel to vary output current from 0 to 10mA in 64 steps... hopefully allowing 0 to 100% on the IN-9 in 64 steps. Anyone see any major errors here? Chase, please let me know if any of this doesn't quite make sense... I was a total noob too when I first joined this list 12+ years ago (I've been reading it every day since, but actually post something about once every World Cup or so). Jeff On Tue, Dec 3, 2013 at 6:53 PM, Chill4844 <[email protected]> wrote: > > > On Tuesday, December 3, 2013 12:43:04 AM UTC-5, jrehwin wrote: >> >> > I hope someone out there has some thoughts on this and is willing to >> help out this noob. >> > >> > The senerio is this: >> > >> > I am attempting to use an Arduino in conjunction with a TLC5940 to >> drive an array of IN-9's (And not kill myself or blow anything up) the >> problem being if i understand it right (which I probably don't) is that >> instead of a positive PWM out the arduino the TLC5940 works by sinking the >> current on the cathode side. I don't think i can use this with my standard >> mpsa42 (and I'm not going to attempt anything until i get some advice) I do >> have some mpsa92's available. >> >> That's a somehat peculiar choice for driving an IN-9, but if that's the >> way you're going, you'll want a common-base setup for your transistor, to >> provide voltage gain but not current gain (the current through the IN-9 >> will still be controlled by the TLC5940). You could use your MPSA42 for >> this (note that I'm just scribbling here, this lashup might not work): >> >> http://www.vitriol.com/images/tech/nixies/TLC5940.gif >> >> Have you read Jan's writeup on driving IN-9s? >> >> http://www.die-wuestens.de/iz/IN9-2.pdf >> >> You might also want to look at some other designs used to drive IN-9s, >> such as Brian Stuckey's Nixietherm: >> >> http://www.tubeclockdb.com/forum/Builders-Forum/1280- >> Nixietherm-IN-9-bargraph-based-thermomer.html >> >> - John >> > > Thanks for the quick reply John, the main reason for he 5940 in this case > is that an arduino does not have enough pwm outs to drive the 14x in-9 > array for my "spectrum analyzer" probably actually an audio visualizer. > Yes I have read that write up on driving in-9's and have done a few > projects with that already. After much research I found something very > similar to the lash up you posted. I just have to figure out weather the > 5940 will sink that much current. If you have any other ideas for driving > 14 of them I am all ears I've been thinking on it for months I could use a > fresh mind. I am sure there is a better way to go about all of this. That's > what I get for being a noob. > > Thanks again John > Chase > > -- > You received this message because you are subscribed to the Google Groups > "neonixie-l" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send an email to [email protected]. > To view this discussion on the web, visit > https://groups.google.com/d/msgid/neonixie-l/d2cb8913-648d-46c7-9878-95050569a952%40googlegroups.com > . > > For more options, visit https://groups.google.com/groups/opt_out. > -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. 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