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Question about Resistors

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sshook(at)cox.net
Guest

Posted: Tue Mar 25, 2008 12:13 pm Post subject: Question about Resistors

Bob et al,  

I am putting together an annunciator panel using some Stanley LED Light Bars PN# (404-1148-ND).  And if I read correctly on the spec sheet from Digikey, the voltage is 1.7v per LED.    

This being the case, do you have a ‘cheat sheet’ showing what resistors I would need to provide the appropriate voltage drop for our 14v OBAM aircraft?  

                                  

Scott R. Shook  

RV-7A (Building)  

N696JS (Reserved)  

     [quote][b]

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rv-9a-online(at)telus.net
Guest

Posted: Tue Mar 25, 2008 2:51 pm Post subject: Question about Resistors

Hi  Scott:

  

 Here's  the formula:  R = (Vbatt-Vf)/If ohms, where Vf is 1.7 V and If is 20 ma  (from datasheet)

  

 For  the part you chose, R = (14.2-1.7)/0.020 = 625 ohms (use 680 ohm standard  value) -- if you power each segment seperately.

  

 If you  connect all 5 of the LEDs in series, then R = (14.2 - 5*1.7)/0.020 = 285 ohms  (use 330 ohm standard value).

  

 Now,  here's one issue to deal with:  If you are dimming the LEDs, you may want  to power each segment separately so that they dim the same as other displays in  the cockpit.  Only experimentation will give you the answer for  this.

  

 Finally, you may want to try one light bar first before you commit to  using them in a panel.  They may have a tendency to wash out in bright  sunlight.  I used to sell a product line that used similar light bars, and  this was an issue unless you carefully shield the display from ambient light  (such as locating right underneath the glareshield).  I found some 1/8"  LEDs that will dazzle your eyes, but they were very difficult to dim due to  their intensity.  Of course, they were tiny and not easy to  label!.

  

 Good  luck.

  

 Vern  Little.

 [quote]   

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hooverra(at)verizon.net
Guest

Posted: Tue Mar 25, 2008 3:41 pm Post subject: Question about Resistors

Scott,  

            You need to drop 12.3V (14-1.7) while limiting the current to ~20ma R=E/I  (12.3/.02 = 615 Ohms). The power dissipated will be P=I*E (.02*12.3=.246 watts).  A 620 ohm 1/2W resistor would be fine for 1 LED. If you connect several LED’s in series subtract the total voltage drop and do the same calculation. 14-3.4 for 2 and so on. LED’s will work over a fairly broad range of current depending on the type and brightness desired so don’t worry too much about exact resistor values. You can work backwards to find the current I=E/R so if you use 560 ohms (12.3/560=.022) or 22ma. Check your Digikey catalog for standard resistor values.  

            Good luck  

         

  

From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Scott R. Shook

 Sent: Tuesday, March 25, 2008 2:59 PM

 To: aeroelectric-list(at)matronics.com

 Subject: AeroElectric-List: Question about Resistors  

  

   

Bob et al,  

I am putting together an annunciator panel using some Stanley LED Light Bars PN# (404-1148-ND).  And if I read correctly on the spec sheet from Digikey, the voltage is 1.7v per LED.    

This being the case, do you have a ‘cheat sheet’ showing what resistors I would need to provide the appropriate voltage drop for our 14v OBAM aircraft?  

                                  

Scott R. Shook  

RV-7A (Building)  

N696JS (Reserved)   	  Quote: 	
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       [quote][b]

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sshook(at)cox.net
Guest

Posted: Tue Mar 25, 2008 4:08 pm Post subject: Question about Resistors

That is the formula I was looking for.  Thank you.  

   

The light bars themselves, have 5 LED’s so those will go in a series.  My last trick will be mounting them and the wiring of said LED’s.  I am hoping a blank project circuit board will do what I want. The trick with the circuit board will be the spacing requirements (space between light bars).  Once that is figured, I can order the face (reverse engraved acrylic).  

   

I am also working on a “push-to test” option.  

   

As far as the intensity, since these will be behind a reverse engraved acrylic (black behind clear) only the letters themselves will light up.  Once I get the mock up completed, the day/night intensity testing will be performed.  

     

                                

 Scott R. Shook 

 RV-7A (Building) 

 N696JS (Reserved)   

        

  

From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Vernon Little

 Sent: Tuesday, 25 March, 2008 15:46

 To: aeroelectric-list(at)matronics.com

 Subject: RE: AeroElectric-List: Question about Resistors  

  

     

Hi Scott:  

    

   

    

Here's the formula:  R = (Vbatt-Vf)/If ohms, where Vf is 1.7 V and If is 20 ma (from datasheet)  

    

   

    

For the part you chose, R = (14.2-1.7)/0.020 = 625 ohms (use 680 ohm standard value) -- if you power each segment seperately.  

    

   

    

If you connect all 5 of the LEDs in series, then R = (14.2 - 5*1.7)/0.020 = 285 ohms (use 330 ohm standard value).  

    

   

    

Now, here's one issue to deal with:  If you are dimming the LEDs, you may want to power each segment separately so that they dim the same as other displays in the cockpit.  Only experimentation will give you the answer for this.  

    

   

    

Finally, you may want to try one light bar first before you commit to using them in a panel.  They may have a tendency to wash out in bright sunlight.  I used to sell a product line that used similar light bars, and this was an issue unless you carefully shield the display from ambient light (such as locating right underneath the glareshield).  I found some 1/8" LEDs that will dazzle your eyes, but they were very difficult to dim due to their intensity.  Of course, they were tiny and not easy to label!.  

    

   

    

Good luck.  

    

   

    

Vern Little.  

  [quote]  

--

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Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

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sshook(at)cox.net
Guest

Posted: Wed Mar 26, 2008 8:33 am Post subject: Question about Resistors

I have lights!  

   

The resistors worked great and my mock up works great.  The pins on the Stanley LED’s are standard to a project board so mounting them will be easier than I first thought.  I am going to do a burn-in and temperature test this weekend to make sure I am not generating heat.  

   

For a low voltage, non-critical application like this, would it be acceptable to use a solder bridge for the pins I need to bridge?  

   

On the 5 LED bars, you have to bridge 2-3, 4.5, 6-7, 8-9.  

     

                                

 Scott R. Shook 

 RV-7A (Building) 

 N696JS (Reserved)   

        

  

From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Scott R. Shook

 Sent: Tuesday, 25 March, 2008 17:01

 To: aeroelectric-list(at)matronics.com

 Subject: RE: AeroElectric-List: Question about Resistors  

  

   

That is the formula I was looking for.  Thank you.  

   

The light bars themselves, have 5 LED’s so those will go in a series.  My last trick will be mounting them and the wiring of said LED’s.  I am hoping a blank project circuit board will do what I want. The trick with the circuit board will be the spacing requirements (space between light bars).  Once that is figured, I can order the face (reverse engraved acrylic).  

   

I am also working on a “push-to test” option.  

   

As far as the intensity, since these will be behind a reverse engraved acrylic (black behind clear) only the letters themselves will light up.  Once I get the mock up completed, the day/night intensity testing will be performed.  

     

                                

 Scott R. Shook 

 RV-7A (Building) 

 N696JS (Reserved)   

        

  

From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Vernon Little

 Sent: Tuesday, 25 March, 2008 15:46

 To: aeroelectric-list(at)matronics.com

 Subject: RE: AeroElectric-List: Question about Resistors  

  

     

Hi Scott:  

    

   

    

Here's the formula:  R = (Vbatt-Vf)/If ohms, where Vf is 1.7 V and If is 20 ma (from datasheet)  

    

   

    

For the part you chose, R = (14.2-1.7)/0.020 = 625 ohms (use 680 ohm standard value) -- if you power each segment seperately.  

    

   

    

If you connect all 5 of the LEDs in series, then R = (14.2 - 5*1.7)/0.020 = 285 ohms (use 330 ohm standard value).  

    

   

    

Now, here's one issue to deal with:  If you are dimming the LEDs, you may want to power each segment separately so that they dim the same as other displays in the cockpit.  Only experimentation will give you the answer for this.  

    

   

    

Finally, you may want to try one light bar first before you commit to using them in a panel.  They may have a tendency to wash out in bright sunlight.  I used to sell a product line that used similar light bars, and this was an issue unless you carefully shield the display from ambient light (such as locating right underneath the glareshield).  I found some 1/8" LEDs that will dazzle your eyes, but they were very difficult to dim due to their intensity.  Of course, they were tiny and not easy to label!.  

    

   

    

Good luck.  

    

   

    

Vern Little.  

  [quote]  

--

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Mark Phillips in TN

Joined: 10 Jan 2006
Posts: 431
Location: Columbia, TN

Posted: Wed Mar 26, 2008 4:39 pm Post subject: Question about Resistors

In a message dated 03/25/2008 3:15:23 PM Central Daylight Time, sshook(at)cox.net writes:

  	  Quote: 	
		  I am putting together an annunciator panel using some Stanley LED Light Bars PN# (404-1148-ND).  And if I read correctly on the spec sheet from Digikey, the voltage is 1.7v per LED.  	


  Hi Scott-

  

 I used the same LEDs and they've worked quite nicely for 4 years/almost 500 hours.  Here's the arrangement I cobbled together:

  

 http://websites.expercraft.com/n51pw/index.php?q=log_entry&log_id=7604

  

 click on foto for larger view.  Drawing available in AutoCAD if you'd like a copy...

  

 From The PossumWorks in TN

 Mark Phillips, RV-6A "Mojo"

 http://websites.expercraft.com/n51pw/



Create a Home Theater Like the Pros. Watch the video on AOL Home.

  [quote][b]

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Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

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_________________
From The PossumWorks...

Mark Phillips in TN

Joined: 10 Jan 2006
Posts: 431
Location: Columbia, TN

Posted: Wed Mar 26, 2008 6:47 pm Post subject: Question about Resistors

In a message dated 03/26/2008 11:37:31 AM Central Daylight Time, sshook(at)cox.net writes:

  	  Quote: 	
		  For a low voltage, non-critical application like this, would it be acceptable to use a solder bridge for the pins I need to bridge? 	


 >>>

 That's exactly what I did, on a standard project board like you mentioned- bend the prongs over and nail 'em with a touch of solder. Only difference is I used the 3-LED blocks instead of the 5...

  

 see: http://websites.expercraft.com/n51pw/index.php?q=log_entry&log_id=5135

  

 I'll also mention that I chose slightly smaller resistors than would normally be called for to brighten them up a bit.  Consider that these annunciators are typically illuminated for relatively short periods of time and even if overdriven, they will likely outlast your airplane.  I tested this by intentionally overdriving sample blocks well over their limit for about two weeks continuous with no failures.  I would also recommend buying several spares of each specific block you use- they are really cheap, and you never know how long an identical item will be available for replacement, if ever needed.  Neat stuff...

  

 Mark



Create a Home Theater Like the Pros. Watch the video on AOL Home.

  [quote][b]

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Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

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_________________
From The PossumWorks...

rv-9a-online(at)telus.net
Guest

Posted: Wed Mar 26, 2008 7:47 pm Post subject: Question about Resistors

Scott:  surf to aircraftextras.com here: http://aircraftextras.com/VxAviation.htm[url=http://www.vx-aviation.com/page_2.html#IL-4A,%20IL-12A_more][/url]

  

 The  IL-4A controller can be used to drive lamps, and support various polarities of  input signals.  It also allows you to connect to your dimmer and supports  push-to-test.

  

 Vern

 [quote]   

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