best way of dealing with this led bar?

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daArry

Well-known member
Joined
Jun 3, 2004
Messages
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Location
londaaan
Hey all...

Just seen this: http://www.rapidelectronics.co.uk/rkmain.asp?PAGEID=80010&CTL_CAT_CODE=30325&STK_PROD_CODE=M29301&XPAGENO=1 which I was thinking I could use for some level indication on the yammy desk i'm reworkin, i'd have 2 sitting either side of the master fader (which is a p+g belt fader - hoping to use with mcs' relay att brd). They would fit perfectly in the already cut panels but the thing is some of the leds are connected in series (shown on datasheet)... would i just treat these as a single LED when using say one of those LM led driver IC's? Or are the other ways to go about it?

Thanks, and happy nye again!

D
 
> the leds are connected in series (shown on datasheet)... would i just treat these as a single LED when using say one of those LM led driver IC's?

The parallel connection of the LM391x chips is cleverly detailed and basically wasteful.

If you can live with Bar-mode instead of dot-mode, use the connection on page 18 of the LM3915 sheet.

LM3915series.gif
 
Hey PRR

So is bar mode when multiple LEDs light up and dot mode when just a single led lights at a time? What did u mean by the 'basically wasteful' comment?

Thanks!

D
 
Hi daArry,

Yes, dot mode is when only one LED is lit at a time- indicating the level at that moment. Bar is when all the LEDs up to the registered level are lit.

The way PRR describes to run the LEDs puts them in series- the power supply voltage therefore has to be a little more than the total combined forward-voltage drops of the LED's. The standard parallel connection allows a much lower LED supply voltage, but each LED will draw more current individually, and if a larger supply voltage is used, this is quite a wasteful way of driving them.

As PRR points out, when connected in series you can't use "Dot" mode. This is because each LED output from the IC is effectively a current sink. Usually in parallel connected LEDs, each LED is connected to +Ve via its anode. Here, in series-connected "low current" mode, each LED depends on the previous LED being forward biased to recieve its connection to +Ve. So the preceding LED has to be "On" for the next to light!

BTW, how did it go with your A77??

Mark
 
Hey Mark

Thanks for clearing all that up - and more :thumb:

A77 - on simmer atm, still on the lookout for one but need to get a few other projects wrapped up first - this console being top priority...need some i/o bigtime!

Cheers,

D
 

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