smallest 5 led mono vu meter circuit diy?

[Gurner]

The reason the simulation doesn't work at 9V with a TL07x is because the default power supply is +/- 15V bipolar.  Just like the power supplies in op-amp appnotes are usually implied.

The ground reference in that sim is therefore the midpoint of the supplies, not the lowest point.  If you swap all the GND points for 4.5V it works, even with a TL07x.

I'm not sure it would because if you used 4.5V as the bias for the +ve pin, then you'd have 4.5V DC on the ouput pin of the opamp = LEDs on all the time (even in series if yellow LEDs used).

I think the only solution here (ie if wanting to use a single supply opamp), is to use a rail to rail input & ouput opamp & keep the bias arrangement as is (in fact even better, tweak the +ve pin bias up a tad to be just below the fwd voltage of the LEDS in play)

[earthtonesaudio]

ALL the ground points.  Meaning the LED cathodes would go to 4.5V as well.

[Earthscum]

but seriously, cheers merlin, ...but i'm going to wait for my AN6884'S now as they are suited for just 5 leds..it'll be nice and small too...(as suggested by Gurner)

I have a pair of AN6884's... I'll have to keep an eye on this. I was going to use mine for IN/OUT 5-bar graphs (6, with "on" status bottom LED, if the bottom of the 5 doesn't stay lit constant). I need some kind of visual as to what I'm feeding my amp out of my chain compared to the straight signal. If it pegs the OUT, I probably bumped a volume on the BF. 

[deadastronaut]

http://www.techlib.com/electronics/bargraph.htm you could also use a 4049 but be aware of the different pin out.

this is worth considering if you have a 49 or 69 knocking about. the first stage can be treated as a tube sound fuzz - simply add input cap, swap input r from 1m to 100k and feedback 1m r for sensitivity pot. maybe play with feedback caps to tailor sensitvity too. could even take an audio out.

i have a 4049 ..i'll try it when i get time , busy busy busy...changing pups+setting up a les paul (old antoria copy, nice though) .pc fresh install for a mate, decorating, wiring lights...barrelling home brew beer...arghhhhh not enough hours in the @#$%ing day...

[Gurner]

ALL the ground points.  Meaning the LED cathodes would go to 4.5V as well.

the problem then is that the 4.5V 'reference' as connected to the cathodes needs to be low impedance (vs a modest impedance when used as a modest impedance Vref for input biasing for an opamp)....a low impedance 4.5V reference means a slightly higher component count (vs using good 'ole  ground & a rail to rai opamp instead)

[merlinb]

..a low impedance 4.5V reference means a slightly higher component count (vs using good 'ole  ground & a rail to rai opamp instead)

How does a rail-to-rail opamp help? A TL07x can swing its output down to around 1.5 to 2V, so as long as the LEDs threshold voltage is a bit more than that, they'll turn off. You can always increase the threshold voltage further by adding an extra diode/zener in series with the output of the opamp.

[Gurner]

..a low impedance 4.5V reference means a slightly higher component count (vs using good 'ole  ground & a rail to rai opamp instead)

How does a rail-to-rail opamp help? A TL07x can swing its output down to around 1.5 to 2V, so as long as the LEDs threshold voltage is a bit more than that, they'll turn off. You can always increase the threshold voltage further by adding an extra diode/zener in series with the output of the opamp.

For a single supply opamp, we've just seen from Rob's earlier DC voltage readings with the no AC signal present, the TL072 input pin sits quiescently at 0.75V & the output pin only swung down as low as 2.2V ...this isn't low enough if you've a Red or Yellow LED connected to the opamp output. (cos the LED will always be on) a rail to rail opamp helps, becuase with no input the output can swing down to 0V = LED off.

Sure, as you've pointed out, you can work around this with a non 'rail to rail' opamp like a  TL072 by *adding* stuff to compensate for the lack of rail to rail swing ability but remember.....the requirement was low component count!

[deadastronaut]

righto, ive recieved my AN6884'S today....yay..

@Gurner:  so i can just bread the example on page 4 of the pdf with 9v yes?....with guitar straight in?...

http://pdf1.alldatasheet.com/datasheet-pdf/view/13421/PANASONIC/AN6884.html

[Gurner]

righto, ive recieved my AN6884'S today....yay..

@Gurner:  so i can just bread the example on page 4 of the pdf with 9v yes?....with guitar straight in?...

http://pdf1.alldatasheet.com/datasheet-pdf/view/13421/PANASONIC/AN6884.html

this will be the point where I go oops, I've just gone back to your first post...

i'm looking for a tiny circuit (for use with guitar input)  preferably transistor..no ic, (it needs to be as small as possible..

I'd overlooked the bit in bold imagined this was going to be T'ing off your guitar signal from another circuit.

unfortunately, the datasheet doesn't say what the input impedance is for the AN6884, but the cct  as shown on page 4 (with the 10k pot at the input) will almost certainly load your guitar signal down ....you could try a higher value pot & hope, but if that doesn't work then it will need a simple buffer in front.

[I'll get me coat]

[deadastronaut]

i'll get it for ya....and ya hat....ok i'm breading it now anyways...

[Gurner]

i'll get it for ya....and ya hat....ok i'm breading it now anyways...

Actually, I'm off the hook (so my coat stays on it!)....becuase the AN6884 block diagram on page 1 of the datasheet, shows the 1st stage is a non inverting opamp....that'll be high impedance (therefore no loading of your signal), so all you'll need to do is have a high value input pot (vs their 10k pot...preferably 1M or 500k)

[deadastronaut]

righto....

got a 500k pot on it, its not acting as a vu though, its just raising  and lowering the leds as i turn the pot up/down....no fluctuation with guitar!!!

edit:

ooopppsss...had leads backwards.....

yayyyyyyyyyy it works.....excellent...cheers G  pukka!!!!....

[deadastronaut]

here ya go...works a treat!....

i  rigged up 9 leds (para) to get <<<< o >>>>   looks great.....

[edd29]

hi rob,  where did  you connect the pot? thanks.

 edd

[deadastronaut]

hi edd,  thats a 1M trim pot on there...

just connect a 1m pot there if you don't have a trimmer...


pin 1 means pin1 of the AN6884..   Its a 9pin  SIL...(iirc that terminology is correct)

[Gurner]

In case it's not obvious....the trim is set & forget (for your gutar type)....the trim could therefore easily be substituted with two fixed resistors (thereby making the final pcb a little smaller & cheaper) - i.e. once you've got the leds responding to your liking, just measure between the wiper & each of the outer lugs to get the two resistor values you need in lieu of the trimpot

[deadastronaut]

^...cool...i recommend  breading it for your guitar signal...

a nice little addition to a pedal, board etc.....

note: when it wasn't working properly, it was a good pot level indicator ....just for kicks...

[PRR]

> "led 1 stays on"

It isn't supposed to. Probably if you replace the 500K-1Meg input pot with a 10K, and shield away from all AC or fluorescents, it will go out.

LED 1 is glowing because the "high impedance" internal gain-stage is not so very high impedance. It weeps a DC current, up to 1uA. In a 1Meg pot that would make 1V even without signal! Which would light LEDs 1-4! Obviously your perticular chip does not weep a whole uA, because even at 500K that would light a bunch of LEDs.

Still, the number of lit-on-silence LEDs will vary with chip, temperature, pot value and setting.

This is where a buffer would be good.

OTOH, one on-LED is no big deal.

[Ronan]

An ebay search on KA2284 brings up some prebuilt modules less than $4 shipped. Bargain!

[deadastronaut]

wheres the fun in that!...

that is cheap , i have 9 super brights though..    <<<< o>>>>

@prr i quite like the centre one on anyway...but thanks for the info..