Ilya

What LEDs do you use for your LED meters?
« on: October 23, 2007, 12:49:59 PM »
I'm going to build my first LED PPM meter and I'm now ordering all the parts needed.
Well, I started browsing through a selection of LEDs available at, say, Farnell and I really don't know where to start. I know, I need leds with around 2V drop (because there are 5V and 12V leds with built in resistors), but the rest makes me scratch my head.
What luminous intensity do I need, angle of light emission, package (well, this is simple but still)?
What do you guys use for your meters? Any advices?

Ilya
PCBs, enclosures and build guides at www.rackneve.com


gswan

What LEDs do you use for your LED meters?
« Reply #1 on: October 24, 2007, 07:27:43 AM »
I use high-efficiency diffused LEDs, since you can run them with lower current which helps keep the power dissipation down for something like the LM3915 in bar graph mode.

Carl_Huff

What LEDs do you use for your LED meters?
« Reply #2 on: October 25, 2007, 12:21:49 AM »
Ilya,

I use LEDTronics Part Number: RL280TWRG4H-3C/05-s tri-color LEDS and drive them with MAXIM 7219 display drivers to keep the brightness up and the current down.  Two MAX7219 chips will drive 64 LEDs and cost you less than $10 US for the pair.  Using tri-color LEDs makes it easy to build the Peak/VU combination displays that are so common these days.  However you need to feed the display drivers with either a MCU, DSP or PIC chip.  A simple LM3915 won't work.

Best Regards,
Carl Huff

Best Regards,
Carl Huff

gswan

What LEDs do you use for your LED meters?
« Reply #3 on: October 25, 2007, 12:50:03 AM »
Very cool. I hadn't seen those drivers before.

AudioJohn

What LEDs do you use for your LED meters?
« Reply #4 on: October 25, 2007, 05:18:04 PM »
It is important to use intensity matched LED's - as a dim one (or bright one) - will stand out when the ladder is fully illuminated.

John G

Ilya

What LEDs do you use for your LED meters?
« Reply #5 on: October 25, 2007, 05:33:19 PM »
Guys, thanks for all your input!
John, how close should those LEDs be matched? I have no idea if intensity of 10 (green LED) will match with let's say 15 (red LED)? And is this intensity sufficient? The spread is really huge - from 3-4 to several thousands....
PCBs, enclosures and build guides at www.rackneve.com

gswan

What LEDs do you use for your LED meters?
« Reply #6 on: October 25, 2007, 05:48:26 PM »
Start by purchasing the different coloured LEDs from the same family, which should have similar quoted intensities for a given current (usually in mCd).

Then you need to match the intensity of each LED you plan to use by hand. I' recommend using a plug-in breadboard to power up the LEDs (with current limiting resistors) and view all the ones for the meter at once. You will see some slightly dimmer/brighter than others in which case you swap them out for others.

Ilya

What LEDs do you use for your LED meters?
« Reply #7 on: October 25, 2007, 06:02:01 PM »
But these numbers are for different colours of LEDs from one family. I just want to know how bright are 30 mCd and 1000 mCd.
Let's take dBx 160. What brightness do those LEDs have? And modern blue ones that are used as a backlit for Focusrite Vocal procesors?
PCBs, enclosures and build guides at www.rackneve.com

gswan

What LEDs do you use for your LED meters?
« Reply #8 on: October 25, 2007, 08:22:52 PM »
30mCd is quite bright on a panel meter - especially if there are many of them on at once. I normally use high-efficiency 3mm LEDs with a quoted range of [email protected] and run them at about 5mA, with a pair at each position. (http://www.us.kingbright.com/kcpartno.asp?txtPartNo=WP934)

Here's a picture of a display running like this so you can see how bright it is (the red LEDs are not lit).




Ilya

What LEDs do you use for your LED meters?
« Reply #9 on: October 26, 2007, 02:58:51 AM »
gswan,
thanks a lot. Now these numbers make sence!
PCBs, enclosures and build guides at www.rackneve.com


 

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