[Recoder2]Need a power LED? This post is for you

[Le Djé]

Hi,

I found this solution to indicate if the recorder is on or off.
Just find one bicolore led (3 pins) and have a look at the pictures!

- no 5v power off : off
- 5V present but power off : Green
- Power on : Orange

I use only one resistor (470 ohm - yellow/violet/brauwn)

You must be logged to view the pictures.

Jérôme (French)

[mdp]

These are common cathode?

[Le Djé]

Yes it is.
Jerome

[mastrand9]

Great & clever solution to annoying problem.  I'm trying to use the Recorder2 for mobile video recording, without active monitor once the rig is set up for a/v capture.  Having separate confirmation of power and unit operation is a big help! Thanks for sharing the idea.

[biking_brian]

Does anyone have a Radio Shack part number for such an LED?

[mdp]

There are 2 types of bicolor LEDs; 2-terminal and 3-terminal.  The design above requires a 3-terminal common cathode bicolor LED.  The only part number I could find at Radio Shack was a 2-terminal LED, 276-012.  You can find the 3-terminal LEDs a lot of places:

Here on eBay you can buy 10 for $5:

http://cgi.ebay.com/3MM-Red-Green-Bi-color-3-lead-LED-Pack-of-10-L303RGD_W0QQitemZ190124487582QQihZ009QQcategoryZ11644QQrdZ1QQcmdZViewItem


More technical data can be found here but it looks like you have to buy 15 for $25 to get any:

http://www.lc-led.com/View/itemNumber/304

[biking_brian]

The Ebay link above was for a 3mm LED, not a 5mm.

Here's a link to some 5MM LEDs.  Would these work, and what resistor would I use with these?  Also, how do you know which terminal is for which color?

http://cgi.ebay.com/5-MM-RED-GREEN-LEDs-3-Lead-Package-of-10_W0QQitemZ5991774971QQihZ009QQcategoryZ19142QQtcZphotoQQcmdZViewItem

Edit:  I checked with the seller and these are common cathode.

[mdp]

The seller doesn't say whether these are common cathode or common anode.  The 3mm LEDs from the same seller are described as common cathode which is what you need.  They come both ways.  I'd ask him.  If they are common cathode, then they'll work.   

The resistor serves two functions; 1) to prevent the LED from burning out and 2) to adjust the brightness to something you will find appealing.  The size of the resistor may be different for Red than Green for the same brightness. If you want the brightest, 50 ohms will probably be adequate for both Red and Green.  The higher the resistor, the lower the brightness.  Some LEDs are very bright at their maximum rated current which is 20 milliamps for most LEDs.  Could be a distraction depending on where your unit is located.   A typcial resistor range to consider is 50 to 500 ohms.

Regarding which lead is which, for the 3mm LEDs the seller shows the shortest lead (anode) is Green, the next shortest lead (anode) is Red, and the longest lead is the cathode which is connected to ground.

If you plan to use this LED in the design posted by Le Djé, note that you won't get Green and Red.  You'll get Green and the combination of Green+Red.  That's why he states the Power On color is Orange.  You can also hook it up so you get Red and the combination of Green+ Red (i.e. Orange).  To get a feel for different color combinations, try the site below. Turn Blue off and the mixture of Red and Green at the same brightness yields Yellow.  Now vary the intensity of Red and Green.  You'll see Orange occurs if Red is brighter than Green, something you can do with the resistors. 

http://www.omsi.edu/visit/tech/colormix.cfm

Here is another option.  Get one of these 4-terminal common cathode LEDs, then choose which two colors (terminals) to use; Blue and Green, Blue and Red, or Green and Red.  Simply ground the unused terminal with the longest lead.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=270120275173

These have a clear lens which can sometimes look awkward in the case.  A diffused look can be obtained with lens cap, here's one from Jameco: part number 14277.

http://www.jameco.com/Jameco/catalogs/c272/P60.pdf

For an RGB LED with a diffused lens, your local electronic store might carry a popular part from Linrose, part number: B4368D1/5/6.  These go for around $5 each.  Personally I prefer the 'smoother' diffused lens look than a clear lens LED with a diffused lens cap however both look good enough in the case.

Here's a diffused 3-terminal common cathode LED already in a PCB mount.  Downside is you have to buy 40.  The seller might sell just one if asked.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=280126933521

[biking_brian]

I finally got around to making the modification as originally posted by Le Djé.  Since my use is in outdoor applications, I wanted the LED bright, so I went with a 47 ohm resistor.  Thanks for all the advice.

[mdp]

The pad to get Power-On indication shown in the last two pictures posted by Le Djé delivers +3.3V.  A red LED will consume around 15mA but other colors like green, blue, etc only consume ~5mA.  Brightness, therefore, is mostly limited by the +3.3V on the board, not the LED.  I'm almost finished with a circuit that takes advantage of the +5V from the adapter and delivers more than 20mA for most any LED.  I've tested red as high as 35mA.  Of course, an LED is required that can handle the current but most LEDs are pretty bright at 20mA, the most common rating.

[biking_brian]

Uh oh, with 3.3V and my 47 ohm resistor, wouldn't that get me 70mA, exceeding the rating of the LED?

[mdp]

Current is computed according to (Supply - Vf)/R where Vf is the forward turn-on voltage of the LED.  Red LEDs are in the range of 1.5V - 2.0V or so.  I've seen some at 2.5V but not often.  Blue and Green LEDs, however, are usually in the 2.5V range.  Assuming a Red LED, taking the pessimistic case current consumption would be (3.3-1.5)/49=.037 or 37mA.  Very high for an average LED.  If it's a 2V LED, the current = 27mA, still higher than the normally recommended limit of 20mA in which case the LED will likely burn out prematurely.  Apparently that's why it's so bright.   Another potential issue is the affect this current load has on the place you tapped it from on the Neuros board.  Hard to evaluate without a schematic.  You could check to see if any components are unreasonably hot.

There are LEDs designed for brightness.  It's the mcd rating to compare.  I couldn't find any bi-color, 3-terminal, common cathode.  These are 4-terminal.  Just ground the unused color by connecting it to the cathode.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=270120275173

And for really bright, and a lot more expensive:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=250076048550

[biking_brian]

With the Neuros turned on, I'm measuring 1.18V across the 47 ohm resistor I added.  That's giving me 1.18/47 = 0.025, or 25mA of current.

In retrospect, maybe I should have gone with a 100 ohm resistor.  But if we're talking about my 25mA versus a rated of 20mA, then I'll be lazy and live with the (slightly?) premature life of the LED.  After all, since LEDs have a long life, slightly less than a long time is still a long time.    If the red LED burns out, then it just reverts back to the original Neuros hardware configuration.   

I left the Neuros powered on for about 15 minutes, and it's a little warm (but not hot) on the bottom side of the board next to the DC jack.  The rest of the board was cool.  I could let the Neuros cool down, then plug in the power but leaving the unit off, but that's not going to tell me anything because the current draw would be less.

Now I see why you've been working on a more sophisticated scheme for a power on LED. 

[mdp]

Second design is complete.  Please follow this post:

http://forums.neurostechnology.com/index.php?topic=8108.0