Tri-Colour LED Level Meter Schematic?

Hi,

A client has asked me to add a simple 3-state level meter to an item, via a tri-colour LED. Does anyone have a schematic for such a device? I've seen it on FX machines and the like.

Thanks in advance.

Hello,
You can deal with attached schema. It's 4 leds level indicator, but you can reduce to 3, and drive a tri-colour led with.
Rgds

Thanks. Is there a way to do it with a lower parts count?

It's been a while since I've built one of these, but you primarily need a buffer for your input, then 3 sets of opamp comparators with an LED. You use the resistors to set the compared voltage for each LED color. Basically follow the right half of his schematic.

Depending on your power supply, it may benefit you to have an LED driver chip which would reduce your parts down from his original schematic.

I've used this two color LED meter in consoles on some secondary signal paths that didn't justify full meters. Signal present (green)/clip (red) indicia was very useful. I also have hold on the peak so it is easier to see.

JR

Circuit uses bicolor LED that changes color with reverse polarity... LED connected between APK+ and APK-

plimousse said:

Hello,
You can deal with attached schema. It's 4 leds level indicator, but you can reduce to 3, and drive a tri-colour led with.
Rgds

Click to expand...

This circuit is not easy to modify for tricolor LED's. To my knowledge, tricolor LED's are 4-pin devices, each pin driving a red, a green and a blue LED, that's why they're also called RGB LED's. They are either common cathode or common anode, so they can't be connected in series.
Colors are produced by additive synthesis (just like the color palette in your favourite word processor). In order to produce the right color, the Led's must be driven by the appropriate amount of current, so the design of such a meter takes a multi-window level detector with 3 logic outputs and a driver for converting a single logic output to the right current distribution (not difficult, just a bunch of resistors).
In most modern applications, this is done by the PWM outputs of a microcontroller.

I have a design like this that can be reprogrammed for either VU meter style, or peak metering etc.

Right now, the design has a rectifier on board. If you don't need it, then this circuit can be significantly reduced.

Cheers

/R



Note - I still need to finish the software for it, and build up a few hardware proto's. The initial proto's were done on an MSP430 Launchpad.

Rochey said:

I have a design like this that can be reprogrammed for either VU meter style, or peak metering etc.

Right now, the design has a rectifier on board. If you don't need it, then this circuit can be significantly reduced.

Cheers

Click to expand...

Can you drive a tricolor LED with that?

yes. it can drive up to 8 LED's.
The microcontroller samples the input over and over again, and runs a simple software comparison ("If Signal is bigger than X, then light up LED A")

Given that the level's we're talking about aren't over a massive dynamic range, it's perfectly possible. The ADC is about 10bits, giving you an effective d-range of ~60dB or so.

I haven't taken this guy to production yet... but my proto works nicely.

Rochey said:

yes. it can drive up to 8 LED's.

Click to expand...

I understand that, but you will access only the three basic colours red, green and blue; if you want to take advantage of the color palette you have to add a resistor matrix or PWM the outputs.
My idea of a proper tricolor level indicator is green, amber and red.

Abbey,

The original poster didnt mention having full access to colors (by resistors or pwm).

Either way, it would be quite easy to add a loop in software that counted to 100, with a instruction to hold red led on for values less than 30 etc...

My next set of products (including this) wil come with the code, so they can be easily reprogrammed if your interested in that kind of thing. (Using the $10 msp430 launchpad Dev kit)

The OP is looking for a simple multi color level indicator. This is a little too modest to throw a computer chip at it.

I though of offering a kit for my micro base peak/vu meter. The got cha for me is that most people are not comfortable with SMD (yet).

If there is interest I may still do something... I lost interest in the kit business a few decades ago, but don't mind sharing. My patents on peak.VU are expired.

JR

... Did I mention I have a pick and places

we already had this topic back in 2004:
http://www.groupdiy.com/index.php?topic=877.msg12305#msg12305

[silent:arts] said:

we already had this topic back in 2004:
http://www.groupdiy.com/index.php?topic=877.msg12305#msg12305

Click to expand...

Thank you for the link.
And I think the most important contribution is this:
http://www.groupdiy.com/index.php?topic=877.msg11321#msg11321

PRR's window comparator tricolor LED meter does work well in the right application -- a simple level meter, especially in places where you don't have room or money for a full LED bar.  a version with a fast time constant is also nice as a supplemental indicator used in conjunction with a mechanical VU or PPM meter, to show transients.

one of the aphex boxes, a "compellor" variant IIRC, used tricolor LEDs to indicate signal level left to right in green and gain reduction right to left in red on the same LED array.  where the two bars overlapped was amber (since both diodes were active in the same lens) -- visually interesting but really not that useful.

ed

edanderson said:

one of the aphex boxes, a "compellor" variant IIRC, used tricolor LEDs to indicate signal level left to right in green and gain reduction right to left in red on the same LED array.  where the two bars overlapped was amber (since both diodes were active in the same lens) -- visually interesting but really not that useful.

Click to expand...

That's often the case. Designers tend to get carried away and add "features" that look good only in the brochures.

abbey road d enfer said:

edanderson said:

one of the aphex boxes, a "compellor" variant IIRC, used tricolor LEDs to indicate signal level left to right in green and gain reduction right to left in red on the same LED array.  where the two bars overlapped was amber (since both diodes were active in the same lens) -- visually interesting but really not that useful.

Click to expand...

That's often the case. Designers tend to get carried away and add "features" that look good only in the brochures.

Click to expand...

That's what engineers do...  ;D

This brings us full circle... Back when I developed my bi-coler LED indicator (decades ago)  I tried to figure out something useful from the "both on" mode and it just wasn't logical or didn't look right.  Green for signal present and red for over load was useful, and adding a 3rd mode would have IMO not improved the utility of the indicator. Perhaps if green and red both on actually made a different third color, but to my eyeballs, it just looked like both green and red. 
=======
FWIW back in the '80s I did a simple threshold meter using a bi-color LED that did use all three modes effectively. The kit for a record playback system from CBS that was mostly dead on arrival in the marketplace was a CX record playback expander.  The system was threshold sensitive so i needed to provide an easy facility for the customer to calibrate playback level for proper decoding.  My solution was a simple long tail pair comparing a rectified DC level from the audio path to a fixed DC threshold. When the audio level was low the LTP would steer all the current to the green below threshold LED. When above threshold only the red LED was lit.  Only when the audio was adjusted precisely at the threshold level would both colors on the LED light up. When not calibrating level it added a nice light show.  8)
======
Over the decades I have killed many brain cells trying to perfect simultaneous display of Peak and VU signal levels. I have seen attempts to overlay bicolor bar graphs or do side-by-side same color displays.  IMO they aren't that easy to read. Think consoles with tens of meters spread across a meter bridge. FWIW mechanical VU meters aren't very good for scanning either.

My favorite is solid bar for VU with floating dot for peak. The natural characteristics of peak always being higher than average (ASSuming similar release times) provides a nice gap between them to make reading independently easier. Different colored LEDs can suggest level making that easier to discern from quick scanning. 

JR

JohnRoberts said:

abbey road d enfer said:

Designers tend to get carried away and add "features" that look good only in the brochures.

Click to expand...

That's what engineers do...  ;D

Click to expand...

[OT] I notice you use the word engineer where I would say designer. Is it really interchangeable? My former british associates used designer for those who actually create things and engineer for those who fix things. [/OT]

My favorite is solid bar for VU with floating dot for peak. The natural characteristics of peak always being higher than average (ASSuming similar release times) provides a nice gap between them to make reading independently easier. Different colored LEDs can suggest level making that easier to discern from quick scanning. 

JR

Click to expand...

Yes, I spent some time too trying to make the best of the limited front panel real estate, but it's all in the past for me.
IMO, VU's are not relevant anymore. All the audio equipment I use, whether live or in the studio, is peak.  Even when I recorded on tape, I didn't like VU's. My first mixer, in '76, was equipped with LED peak-meters (primarily because it was much cheaper than the SIFAM meters).
I dare say that VU-meters are inadequate (except for calibration). I know there are people who swear by mechanical VU-meters for tape recording, based on the assumption that tape saturation behaves more or less like a VU-meter, but it just doesn't work for me. I won't start a debate...
Anyone who's recorded a set of claves knows what I mean. And I can't think of any application where a VU-meter would be more useful than a peak-meter.

abbey road d enfer said:

JohnRoberts said:

abbey road d enfer said:

Designers tend to get carried away and add "features" that look good only in the brochures.

Click to expand...

That's what engineers do...  ;D

Click to expand...

[OT] I notice you use the word engineer where I would say designer. Is it really interchangeable? My former british associates used designer for those who actually create things and engineer for those who fix things. [/OT]

Click to expand...

I didn't infer anything with my choice of words... Engineers also drive things but the association implies that they understand the technology so can fix and keep stuff (like the train) running. You need to understand how stuff works to design with it, or at least we used to.  8)  Way back when recording engineers were much more involved with the equipment often rolling their own.

My favorite is solid bar for VU with floating dot for peak. The natural characteristics of peak always being higher than average (ASSuming similar release times) provides a nice gap between them to make reading independently easier. Different colored LEDs can suggest level making that easier to discern from quick scanning. 

JR

Click to expand...

Yes, I spent some time too trying to make the best of the limited front panel real estate, but it's all in the past for me.
IMO, VU's are not relevant anymore. All the audio equipment I use, whether live or in the studio, is peak.  Even when I recorded on tape, I didn't like VU's. My first mixer, in '76, was equipped with LED peak-meters (primarily because it was much cheaper than the SIFAM meters).
I dare say that VU-meters are inadequate (except for calibration). I know there are people who swear by mechanical VU-meters for tape recording, based on the assumption that tape saturation behaves more or less like a VU-meter, but it just doesn't work for me. I won't start a debate...
Anyone who's recorded a set of claves knows what I mean. And I can't think of any application where a VU-meter would be more useful than a peak-meter.

Click to expand...

The love for mechanical VU meters was mainly from experienced recordist who had already earned how to apply appropriate windage for different crest factor sources. This is learning how to record "despite" the VU meters.  ;D

The extra apparent resolution around 0VU with mechanical meters is of limited utility IMO.

JR