Input level indicator

[Beo]

Is it advisable to use a zener diode and led configuration below to add an indicator for tune-able input level? The idea would be to strum a chord at max guitar volume and adjust trim or input level pot until a strong led response is seen. R value could be tailored for desired or ideal input level. The boosted input signal could be put through a separate buffer before going to this indicator circuit if necessary.

Or is this really only good for DC voltage?

[boogietone]

I think that you would want this driven by a buffer.

[R.G.]

It is quite difficult to make discrete schemes like this work well with guitar levels. Guitar level is around 100mV, and there are no 100mV zeners. You'll have to ampliify the signal - a lot - to make the signal big enough to start zeners conducting.

As an alternate, look up the LM3915 and/or LM3916 chips which take an input voltage, which can be set up to be AC, and convert it to a 10-LED "meter" of the signal level. You'll save yourself a lot of time and effort.

[Beo]

Thanks RG, that makes sense. Those chips are 18 pins, so that's some serious real estate on the pcb.

[waltk]

Doesn't have to be big.  You could do something like this off-board.  It's an AN6884 set up as a 5-led meter.  Glue the thin PCB to the chip, fold the pins over, and solder.

[armdnrdy]

Meter craziness  

http://www.diystompboxes.com/smfforum/index.php?topic=98118.60


Same animal for 28 cents.

http://www.taydaelectronics.com/an6884-5-dot-led-driver-ic.html

[Beo]

thanks for the ideas and links.

[deadastronaut]

@walt:

remember we had 'ripple' issues with the AN6884's..(gutted as i bought a few of those)

it works fine, but at the very , very end of a dying note/led it had a little 'flutter' on it as reported by another membe QUAD , and tested by myself...same result. faint, but its there.....  
http://www.diystompboxes.com/smfforum/index.php?topic=103564.20


there is this which i haven't tried yet...but stallik (kevin) briefly did. its for fretboard lights ( 9 leds apparently)



@travis: might be worth sticking on a breadboard to try..

[GibsonGM]

I can confirm Astronaut's TL072 solution above. Tried it out, works GREAT for this kind of application.  It may be sensitive to different LEDs....worked best for me using small the 3mm super bright jobs.    With just a tad of tweaking, I believe this could easily do what the OP wants.

It would also work well to drive an LDR - kind of a "poor man's envelope"....

[tca]

Or... just look for old amateur radio schematics and use a analog meter. I have a schem somewhere that I can post if you like (have to look for it). It has a JFET and BJT and a couple of resistors and capacitors.

[tca]

Here it is:



Cheers.

[PRR]

> Here it is:

That's a DC Voltmeter.

An "audio level meter" is not only an _AC_ meter, it needs attack/decay filtering appropriate to audio.

But the "big problem" is: analog needle-meters have become hard to find. Digitals have taken over. Yes, some cheap needle-meters are available. Few are the 50uA rating in that plan, 1mA is more common. In part because needle-meters are sensitive to shock, and cheap 50uA meters won't take any abuse (not even shipping??).

Four LEDs can be danced with an LM339, adjustable thresholds, low-low loading. The simple form lacks attack/decay filtering so may be hard to read. A full audio levelindicator is more than a couple parts.

[tca]

^ One just need to add boost, a full wave rectifier and a cap.

[duck_arse]

mpf105? good luck finding those.