How to build a bi-color led signal meter...

I want to build a simple led signal with a bi-color led (green-red), exactly like the original SSL 4 channel preamp...

The green led have to light up when there is a signal (-60dB ???) and the red when the signal reach 0dB, better -1dB...

Anyone know if there is a simple way to do it ? maybe with a dedicated IC ?

Neeeeeeno

If you want to use an existing circuit, you could just use an LM3916. Then install one bi-colour LED instead of 10 normal LEDs.

Best regards,

Mikkel C. Simonsen

you could do it using Peter C's 4 led meter. Just use trim pots instead of the resistors R7 or R8. You might have to play around to get it to work just right. It uses the LM339.

Vetsen

> simple led signal with a bi-color led (green-red),

http://www.groupdiy.com/index.php?topic=877

> a signal (-60dB ???)

-60 is usually too low. -40 and even -20 have been useful.

(In my main hall, even the -35 will flicker constantly from subsonic rumble.)

double

you will need to convert your signal to a dc voltage. this can be done many ways, i would go with a true rms converter like an analog devices 737 chip and feed that signal to a comparator, which you could either make out of an opamp, or buy form radio shack.

I saw some really cool led meters at the aes show. Dorrough:



Dorrough

Those Dorrough loudness meters have been around for a long time, and they're great. They're used a lot in broadcast facilities.

[quote author="NewYorkDave"]Those Dorrough loudness meters...they're great.[/quote] And they have a price that is "great" too. And i don't mean that in a cheep way...

Price?

You wouldn't believe what good broadcast stuff costs. $300 is nothing!

how about a tri-color instead of bi green/yellow/red

[quote author="NewYorkDave"]You wouldn't believe what good broadcast stuff costs. $300 is nothing![/quote]

That's for the small versions, the full-size meters are more like $450 to $500, depending on the vendor.

Is there a feasible way to DIY a meter with such accuracy? All the LED meters I seem to find plans for are 4 to 10 LEDs. Nothing as large as the Dorrough meters' 40 segments.

Daniel

[quote author="AudioJunkie"]Is there a feasible way to DIY a meter with such accuracy?[/quote]
I guess you could use three LM3915s with "off-set" input signals for a 30dB meter...

There are schematics showing 20-LED meters in the LM3915 and 3916 datasheets as far as I remember.

Best regards,

Mikkel C. Simonsen

Hi Everyone!

Long time lurker here and have learned a TON!! Just so you know, I'm a Noob, like many others out there lurking, but possibly have a solution to this question. This circuit that I'll link to in a sec could help out with this question significantly as it daisychains 3X LM3914's to give a 30 LED readout. I'm using it currently as a lambda meter in my Turbo Fiero and it works incredibly well. Here's the schematic http://www.dohcfiero.com/Images/30led/30led_lambda.gif. It is quite an accurate circuit for what it was designed for but it reads voltages of 1.5v to 3.0v DC. I'm sure it can be tweaked to fit your needs.

There is another 10 segment LED scale using only a single LM3914 located here http://www.dohcfiero.com/Images/diagram.jpg that reads from 0 to 1 volt DC. Once again, I'm quite sure it can be tweaked...

Hopefully this helps you out a bit

If a bi-colour LED meter is something you know and like, then fair enough, but I once prototyped one and decided against it. Seems like the eye is a lot less sensitive to an LED changing colour than it is to a separate signal and clip LED...I personally don't think it works as well as having a separate LED for each. Your call...

Bjorn

[quote author="Bob_Neumann"]This circuit that I'll link to in a sec could help out with this question significantly as it daisychains 3X LM3914's to give a 30 LED readout.[/quote]
Just remember that the 3914 is linear. The 3915 is logarithmic, which is better suited for audio use.

Best regards,

Mikkel C. Simonsen

...and with 3915's, you have to set the ref voltages between the three units (however many you are using) logarithmically as well...I've got a 30 LED one where I got that wrong and simply used the internal refs stacked one on top of the other...makes for a rather odd scale!

Bjorn

check out this link with detailed information on how to build an LED chain based on the LM3915:

http://sound.westhost.com/project60.htm

cheers,


michael

There's a nice bi-led circuit in the Rane MS1-schematic:


http://www.rane.com/pdf/ms1bsch.pdf

Ah well, I saw the Rane-sch was already mentioned in the referenced thread. Well, that's already two people liking it :wink:

I think i will use the 3916, and use it in dot mode.
I'm just wondering if i can connect multiple out at the same led.

For example:
connect togheter pin 1 with pin 14-18. (green led)
and pin 10-14 to the red led.

anyone know if it's possible without damage the IC ?`

Neeeeeeno (aka Noooookie)