Multiple LED voice volume bargraph

Thread Starter

Cyprobe

Joined Mar 5, 2016
7
Hey there everyone!

Been reading AAC website for a while, but recently decided to sign up and join the community :).

Currently I'm trying to combine the non-inverting amplifier experiment:

http://www.allaboutcircuits.com/textbook/experiments/chpt-6/noninverting-amplifier/

with one of your users blog posts (Wendy):
http://forum.allaboutcircuits.com/blog/leds-555s-pwm-flashers-and-light-chasers-index.378/

in order to make an LED bargraph connected to a mic (electet). The volume of the voice input to the mic will determine the quantity of LEDs ON - the louder the sound, the more LEDs turned ON. (I guess it's possible to do it easier with just transistors, but i want to use an op-amp, for fun ;)).

So i was tinkerring a bit and it worked, BUT as i plan to work with a 9V battery max, i can't go beyond 4 leds (voltage drop becomes bigger than Vsupply, as LEDS are in series, as I understand)...

Do you guys think it's possible to redesign the bargraph so a 9V battery could turn ON, say, 10 LEDs and not in the same time?


Thanks a lot in advance and hope I stated my problem clearly! :D
 

shteii01

Joined Feb 19, 2010
4,647
I did not look at schematic... but, you could add batteries. You can have two 9 V batteries in series, that would give you about 18 volts. Since you have 4 led now, with second battery you can have 8-9 led.
 

Thread Starter

Cyprobe

Joined Mar 5, 2016
7
I did not look at schematic... but, you could add batteries. You can have two 9 V batteries in series, that would give you about 18 volts. Since you have 4 led now, with second battery you can have 8-9 led.
Thanks for your reply.

I understand what you mean, but actually I'd like to avoid to add additionnal batteries (if it's possible) and stick with a 9V.
 

shteii01

Joined Feb 19, 2010
4,647
Here's a completely different way.
ok, i am confused. says it can operate from single supply. what is pin 3 connected to? if i use 9v battery, would it go to positive terminal of the battery? also the led, the positive leg of led connected to the positive terminal of the battery too?
 

shteii01

Joined Feb 19, 2010
4,647
Pin 3 is clearly labeled V+
So are the LEDs.
V+ means, "The positive voltage source."
yes, and in the very first schematic in the beginning of the datasheet (page 1) is shows 12 to 20 volts there. i think i saw only one circuit in that datasheet that used 9v battery, everything else was 12 to 20 volt.
 

AnalogKid

Joined Aug 1, 2013
8,259
yes, and in the very first schematic in the beginning of the datasheet (page 1) is shows 12 to 20 volts there. i think i saw only one circuit in that datasheet that used 9v battery, everything else was 12 to 20 volt.
Page 1 of the datasheet says the operating voltage range is 3 to 25 V. Of course, that entire voltage range does not apply to all possible application circuits.

ak
 

#12

Joined Nov 30, 2010
18,182
I was still hoping for a chip-free 'primitive' circuit
Don't worry. This chip is at least 20 years old.:p
And don't forget its brothers, a linear step display and a VU meter.
LM3914, 3915, and 3916 if my brain is working today.
(I can never be sure.:()
 

Thread Starter

Cyprobe

Joined Mar 5, 2016
7
Tough to redesign it for you if you don't show what design you have in place now.
Sure, you'll find an uploaded png image of the circuit diagram (which happens to work) in this reply.
Edit: it's basically the two circuits which i linked in my first post, combined together (and + MIC).

Most of the chip-free designs depend on the LEDs being stacked in series, which raises the operating voltage about 2 V per LED.

ak
Ok then it is set :D.
 

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dannyf

Joined Sep 13, 2015
2,197
Ok. The approach shown above have poor turn on ans turn off chartacters - meaning that the leds turn on and off gradually. Most people don't like that thus it is rarely used.

A very simple approach would be to program a comparator like tl431 to set the on / off charteristics. One tl431 for each led.

For smaller turn on or turn off points, use npn or n CH logic FET.
 

Thread Starter

Cyprobe

Joined Mar 5, 2016
7
...the leds turn on and off gradually...
Yeah I noticed that. Personally i don't mind but a non-gradual turn on would be better.

Could you please specify why chose the tl431? Over any other op-amp?

Edit: I glimpsed on a datasheet, and it seems to be a high-temperature voltage regulator.
 

#12

Joined Nov 30, 2010
18,182
Could you please specify why chose the tl431?
The TL431 is a rather amazing chip. Originally billed as an adjustable zener diode, it can also be viewed as an open collector comparator with internal 2.5V reference. It's good to about 10KHz and can drain 150 ma. Look at the applications and realize how versatile this chip is.
 

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