| Author |
Message |
Jack Conrad (Jackconrad) (204.193.117.66)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, July 18, 2004 - 11:45 am: | |
Now that I have the LEDs and resistors for my dash and switch indicator lights, I have another question. I know the resisitor can go on either the ground or "hot" side of the LED, but are there any advantages of one position over the other? Thanks in advance, Jack |
Abajaba (12.217.192.62)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, July 18, 2004 - 12:32 pm: | |
The LED will work the same with the resistor in either position as you say. I would say whichever is most convenient for mounting for you.
Trying to visualize the circuit in my head and I can't see a reason for one way or another right now. |
S.M. Heath (66.82.53.77)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, July 18, 2004 - 3:13 pm: | |
It probly dosen't matter in your case but, as a genral rule resisters in one color LED's as I know it, mostly are (unless the LED's are used as a Switching device in a peticular Circuit.) conected to the Negitive side. I think the theory with that is, Current "flows" from NEG. to POS.. But I Don't think it makes any difference in LED's used soley for Ilumination (as lights). S.M H. |
Gary Stadler (Boogiethecat) (68.7.217.217)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, July 18, 2004 - 10:05 pm: | |
Electronics engineer talking here....
**It doesn't matter**
Look at it this way... you have a pipe with water flowing thru it and you want to reduce the amount of water coming out. It's just the same if you put a restriction on the inlet or the outlet of the pipe....
Same with an LED. The resistor limits the current that will flow through it, and it makes absolutely NO difference if it's on the (+) or the (-) side of the LED.
Cheers
Gary |
BrianMCI96A3 (65.173.87.107)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, July 18, 2004 - 10:12 pm: | |
It does not matter where the resistor is placed in the circuit, either at the neg. end of the circuit, the pos. end of the circuit or anywhere in between so long as the circuit is in series (has only one path between negative and positive sides of the battery.)
So, as Aba says, wherever it is convenient.
Brian |
Stan (68.150.152.113)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, July 19, 2004 - 8:53 am: | |
The only potential problem is of an accidental short to the common ground. With the resistor in the hot side, a momentary short on the LED will cause no permanent damage. If the resistor is in the ground side, it will burn out the LED. If you have never caused a spark while playing around in the dash of a vehicle, I congratulate you. |
(199.232.244.122)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, July 19, 2004 - 9:28 am: | |
Authentication ErrorYou must enter something as your username. |
John that newguy (199.232.244.122)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, July 19, 2004 - 9:29 am: | |
Not that this makes a world of difference, but:
http://www.talkingelectronics.com/html/Page01.html
Question 8. Can the current limiting resistor be put on the anode lead?
Ans: Yes. It doesn't matter which lead has the current limiting resistor, providing it is always included.
more here:
http://www.kpsec.freeuk.com/components/led.htm
Keeping the polarity of the LED correct, is important. |
Juan Navarro (Jnavarro) (205.216.149.149)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, July 19, 2004 - 11:45 am: | |
Just thinking out of the box here,
If you have a larger wattage resistor to ground, could you use it as common ground for all the negative leads of the LEDs??
Cheers,
Juan PD 4104-148 "Hound. |
John that newguy (199.232.244.122)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, July 19, 2004 - 11:52 am: | |
No. One of those sites explains why, in great detail. |
Gary Stadler (Boogiethecat) (68.7.217.217)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, July 19, 2004 - 7:50 pm: | |
Actually Juan, you could, and you wouldn't need a larger resistor. That said, it's still not a good idea to try to use one resistor for more than one LED for a bunch of engineering reasons.
For one, a penalty would be that as more LED's came on, the lit ones would get less bright, or maybe not work at all if they were diffferent colors hence different voltage drops than other LED's in the mix.
So technically the answer is "yes" it would be OK to use one resistor to ground from the negative leads of many LED's. It won't hurt anything. I've designed some cheepo 7 segment displays this way, and it sufficed. But it may not give you results you like.... |
Abajaba (12.217.192.62)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, July 19, 2004 - 11:32 pm: | |
Hi Juan:
In answer to the question of using one resistor for multiple LED's, Gart states it quite well. |
John that non-nerd (199.232.240.16)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, July 20, 2004 - 8:28 am: | |
I dunno Gary (or is it Gart?), but the following struck a strange chord:
Why Engineers Don't Write Cook Books
Author Unknown
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Chocolate Chip Cookies:
Ingredients:
1.) 532.35 cm3 gluten
2.) 4.9 cm3 NaHCO3
3.) 4.9 cm3 refined halite
4.) 236.6 cm3 partially hydrogenated tallow triglyceride
5.) 177.45 cm3 crystalline C12H22O11
6.) 177.45 cm3 unrefined C12H22O11
7.) 4.9 cm3 methyl ether of protocatechuic aldehyde
8.) Two calcium carbonate-encapsulated avian albumen-coated protein
9.) 473.2 cm3 theobroma cacao
10.) 236.6 cm3 de-encapsulated legume meats (sieve size #10)
To a 2-L jacketed round reactor vessel (reactor #1) with an overall heat
transfer coefficient of about 100 Btu/F-ft2-hr, add ingredients one, two
and three with constant agitation. In a second 2-L reactor vessel with a
radial flow impeller operating at 100 rpm, add ingredients four, five, six,
and seven until the mixture is homogenous. To reactor #2, add ingredient
eight, followed by three equal volumes of the homogenous mixture in reactor
#1. Additionally, add ingredient nine and ten slowly, with constant
agitation. Care must be taken at this point in the reaction to control any
temperature rise that may be the result of an exothermic reaction.
Using a screw extrude attached to a #4 nodulizer, place the mixture
piece-meal on a 316SS sheet (300 x 600 mm). Heat in a 460K oven for a
period of time that is in agreement with Frank & Johnston's first order
rate expression (see JACOS, 21, 55), or until golden brown. Once the
reaction is complete, place the sheet on a 25C heat-transfer table,
allowing the product to come to equilibrium.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
BTW, some of my best friends were engineers! In fact, one recited
this to me:
How many engineers does it take to screw in a light bulb?
Who cares. How'd they get in there in the first place?
HAR! |
Juan Navarro (Jnavarro) (205.216.149.149)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, July 20, 2004 - 7:40 pm: | |
Thank you guys,
I'm only a gear head and not a sparks and wires kind of guy,
Here is another from us engineers:
Comprehending Engineers --Take One
*************************************************
A pastor, a doctor and an engineer were waiting one morning for a particularly slow group of golfers.
The engineer fumed, "What's with these guys? We must have been waiting
for 15 minutes!"
The doctor chimed in, "I don't know, but I've never seen such ineptitude!"
The pastor said, "Hey, here comes the greenskeeper. Let's have a word
with him."
[dramatic pause]
"Hi George. Say, what's with that group ahead of us? They're rather slow,
aren't they?"
The greenskeeper replied, "Oh, yes, that's a group of blind firefighters.
They lost their sight saving our clubhouse from a fire last year, so we
always let them play for free anytime."
The group was silent for a moment. The pastor said, "That's so sad. I
think I will say a special prayer for them tonight."
The doctor said, "Good idea. And I'm going to contact my ophthalmologist
buddy and see if there's anything he can do for them."
The engineer thought for a second and said, "Why can't these guys play
at night?"
Juan PD4104-148 |
Abajaba (12.217.192.62)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, July 21, 2004 - 12:19 am: | |
Oops, Sorry Gary. My bad. Fat fingers and tired is a bad combination for trying to spell properly.
I will now go take a time out in the corner,
with a beer.
Abajaba |
Gary Stadler (Boogiethecat) (68.7.217.217)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, July 21, 2004 - 10:03 am: | |
Hey, I've been called worse!!
Beer huh? I thought corners were for punishment!!
;) |
Abajaba (12.217.192.62)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, July 21, 2004 - 8:37 pm: | |
Sssshhhhhhh!!!!!!!! |
Stephen Fessenden (Sffess) (65.154.176.223)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, July 26, 2004 - 8:29 pm: | |
Jack, I would use the resistors on the hot side. Shorts are possible in any system. The sooner you limit the current the better. The resistor does not need to be at the LED. It could be placed at any point, including right at the light switch or at the power terminal for that circuit. If the resistor limits the current to 100 ma for a circuit, that is approximately what a short circuit current would be also. A little higher but close. I have had an electrical fire in instrument wiring in a van that would not have occured with current limitation on the hot side.
If it cannot be placed on the hot side then the ground side is OK, but I prefer the hot side.
It is also better to allow the resistor to be exposed to air for cooling unless you are imbedding it in a heat conducting epoxy or other heat conducting insulation. Short a reisitor and feel the heat to get the worst case scenario of the heat to be dissipated. |
Stephen Fessenden (Sffess) (65.129.241.114)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, July 26, 2004 - 8:54 pm: | |
Resistor should cover multiple LEDs in series. It is more efficient. I set up lighting with the maximum number of LEDs in series that will fit the formula, usually 6 to 7 for 24 volts. In instrument lighting, the only problem is assuring that there is not a complete loss of lighting. LEDs do not burn out like Christmas tree lights. They last forever. (100,000 hrs) so a good series set is not a problem. If you run them with a separate ballast rsistor for each LED you will use much more current, most of it heating the resistors. I have had my aisle night lights, made of 7 LEDs in series and a ballast resistor, on continually for nearly 2 years now. I have plans to rewire the lighting in my RV switch panel, 40 switches plus guages, with LEDs and leave it on permanently. Amber or red works better for full time lighting since it is easier on the eyes when you want to sleep. Amber is more acceptable since a red glow from a window has other meanings. |
Stephen Fessenden (Sffess) (65.129.241.114)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, July 26, 2004 - 9:22 pm: | |
Jack, after the resistor the wire size can be very small, probably even 28 ga., smaller than you would want to use. |
Stephen Fessenden (Sffess) (65.129.241.114)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, July 26, 2004 - 9:30 pm: | |
I am mountin my LEDs in plastic sheet material now. I drill a 1/4" tight hole for each LED and push it into place. I use a piece of plastic with a smaller hole or holes as a pusher so I am pushing on the body of the LED withthe wires sticking through the hole. I prefer this to perfboard. Plastic can be any color, clear or mirror. Drill slowly so the plastic does not melt from friction. Look at the LED itself and learn how to tell polarity. It is easy once you look. |
mrpuppy (66.233.210.210)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, August 01, 2004 - 5:28 pm: | |
You folks never cease to amaze me. Just when i have a concern, you have the answer. THANK YOU |