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.
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.
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