nixie VU meter

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5 years 6 months ago #3462 by gideon
i love my nixie clock from PV-electronics and while i'm waiting for the parts to build a nice headphone amplifier i was thinking that it would be nice to make a VU meter with IN-9 or IN-13 tubes. does anyone have a design (preferably without micro controllers) that works. i'm not looking for exact measurements, it's more for the visual effect.

i heard some things about using the LM3915 to do this but i have no idea how to use this with these tubes as the LM3015 is made for LED displays.

preferably it would be something with an OPAMP and a transistor like the MPSA42. just plain and simple :)

any hints or suggestions?

p.s. i know about the "that2252" but it's hard to come by and i prefer to use common parts so that if something breaks i don't have to search everywhere for obsolete parts.

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5 years 6 months ago #3465 by gideon
vicsys.hu/files/pop_p0141_000.html i stubled upon this schematic, what is the general opinion about it?

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5 years 6 months ago #3467 by Ty_Eeberfest
Looks like it should work. However, I don't see anything in that circuit that performs linear - logarithmic conversion function, so it's not gonna be accurate.

I also don't understand why OP2 and OP4 are needed (though they don't cost anything since they're part of the LM324 already). They look like they are functioning as unity gain non-inverting amplifiers, so what is the point? Maybe somebody here can help me out for my own education?

Look into it later when the dust is clearing off the crater.

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5 years 6 months ago #3468 by gideon
yes it looks like a unity gain buffer, you "could" make that a lin to log converter with a simple diode in the feedback path. i don't really see why it can't be done and it would be a nice addition.

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5 years 6 months ago #3473 by gideon
nobody has done this or has a nice idea?

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5 years 6 months ago - 5 years 6 months ago #3474 by Mr.Nixie
Why not using simple 2 x 24V 40mA bulbs as series resisitor for the IN-9.
Due to their filament temperature depending resistance it is possible to create a simple (but not fully exact) lin to log conversion



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Last Edit: 5 years 6 months ago by Mr.Nixie.

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5 years 6 months ago - 5 years 6 months ago #3475 by keaster

gideon wrote: vicsys.hu/files/pop_p0141_000.html i stubled upon this schematic, what is the general opinion about it?


I'm currently working on this right now. It seems straight forward to build with easy to find parts but I am having a couple of problems, I can only get the tube to light up half way with about 2v at the RCA input even with more voltage it just stops but 2v still seems too high even for an audio input. Any one with any ideas?

Solved my own problem. You have to play around with the 2 trimmers. I know the original site was not in english Chrome does a good job on translating it but I could not find anything on the trimmers
Last Edit: 5 years 6 months ago by keaster.

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5 years 6 months ago #3476 by Mr.Nixie
Most of the IN-9 / IN-13 need a "burn-in" procedure as they are not able to display the complete lenght right out of the box. They need to be powered for a short time (until the glow reaches the upper making) with overcurrent.
So simply remove OP2 and OP4. Than short circuit C-E on T3 / T5 to feed the maximum current into the IN-13 (set P3 / P4 for this procedure to its 0 ohms position).
Than wait until the glow reaches the upper red marking on the tube's bulb.

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5 years 6 months ago #3487 by gideon
very interesting idea about those bulbs, is that the actual schematic from your own VU meter kit?

but why are people desperatly avoding the use of a linear to log OPAMP. it seems a lot easier to just stick a diode into the feedback path of your OPAMP than to use lighbulbs or expensive chips like the THAT chips

keaster, so you got it to work :D show us the pictures :cheer:

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5 years 6 months ago #3489 by Ty_Eeberfest
Lin-Log by use of opamp + diode: I got interested in this idea after you first mentioned it here, and made a pretty good effort at researching it (though I did not actually breadboard any test circuits). What I found is that all the lin-log circuits in app notes and in other peoples' designs 1) invert the signal, and 2) require a "split" (+12 and -12) power supply.

Do you have a design that is non-inverting and uses a single supply voltage? If so, I'd be interested in seeing it. Or were you just going to deal with the "complications"?

Look into it later when the dust is clearing off the crater.

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