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Phil23
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Joined: 27/03/2016
Location: Australia
Posts: 1667

Posted: 09:26pm 06 Jun 2018

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Hi all,

I have a few 8 & 10 DIL Led Bar graphs, or whatever they are called.

Just want to grab some bussed resistor arrays to make life easier.
Only using the for compact status indicators.

Question is what value resistors should I use.

Examples I see are all over the shop.

The manual shows 82Ohms
The E100 has a couple of Leds with 470Ohms,
Think I've also seen 190 elsewhere.

Also does the value vary depending on whether the pin driving it is configured as OC?

I am aware that different colours have slightly different requirements, and some of my bars are multi colour, but assume I can ignore that as long as I'm in the ball park.

Thanks

Phil.

CaptainBoing

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Joined: 07/09/2016
Location: United Kingdom
Posts: 2171

Posted: 10:17pm 06 Jun 2018

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I don't think there is a standard approach - it all depends on how bright you want 'em and what colour they are. Generally, it seems that people tend to drive them at about 20mA but this is way too bright for simple indicators unless they are to work in bright sun. In normal circumstances I would play around at whatever voltage I am after so I get them bright enough coz I often think 5mA will do and they are still way too bright (esp red LEDs).

personally I think there is a trend for over-bright power LEDs... the devices I am building just lately use 1K on a red SMD LED, which gives about 1.5mA. Plenty bright enough to see the indicator but doesn't blind you. I have even taken to smudging over the surface with a black marker on some - the office is lit up like a flippin' Christmas tree otherwise!

I find you only need to "drive" an LED if you want them for lighting, otherwise keep the power low.

my personal opinions & choices.

Grogster

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Joined: 31/12/2012
Location: New Zealand
Posts: 9751

Posted: 10:48pm 06 Jun 2018

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I also tend to stick to 1k on all 3v3 output pins to LED's. Super-bright and SMD LED's usually need about four times that value to prevent opening a wormhole to another dimension.

With super-bright or SMD LED's, I use 4k7 on 3v3 outputs, and they are plenty bright enough. Blue LED's are the easiest for the Human eye to see so they can appear VERY bright, so I tend to use upwards of 10k on those on 3v3 outputs. This means you can still see the blue light easily, but it does not try to blind you.

Standard diffused LED's, I tend to use around 560R or so. I have used LED bar-graphs on things, and I used 1k resistors on those. I would setup on bar-graph on a prototyping board, and play with resistor values on a 3v3 supply. As a general-purpose indicator for something, you don't want them that bright as Captain says, but it does come down to personal preference, really.

Smoke makes things work. When the smoke gets out, it stops!

skyv
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Joined: 14/03/2015
Location: Australia
Posts: 14

Posted: 11:46pm 06 Jun 2018

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Perhaps one should also consider how many leds are to be on at the same time and the maximum current available from the driving device.

erbp
Senior Member

Joined: 03/05/2016
Location: Australia
Posts: 195

Posted: 12:42am 07 Jun 2018

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I am using some of these as status indicators also. I drive them from a 74HC04 inverter powered at 5v using a 1k5 resistor. Plenty bright enough. The 1k5 on a 5v source gives a roughly equivalent current to a 1k on a 3.3v source.

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