LED rules of thumb

[ian.bird@xxxxxxx]

Web site:- Yes I can, it is just a question of finding the time. I am
currently working on the serial controller for my relay boards and
ideally
will make good progress quickly. If anyone wants to put a skeleton
together
I am more than happy to host it.

Rules of thumb:
Read the specs on the LED particularly regards max current. Most of
these
will be around 20 to 30 ma.
Get a mutlimeter (if you're doing this sort of thing you should have
one
anyway) which can measure current in these low ranges, say 0 to 40 ma or
0
to 400 are typical values.
Connect the LED the correct way round. Usually the long leg is +ve but
not
always so check. Assuming you have a largish resistor there is usually
no
damage if you get this wrong.
Start with a larger resistor, say 1k at 12 volts should be safe. Work
down
till the brightness is correct or the current is max or you are happy.
Somewhere at or around 470 is usually good.

Doing it this way should be safe for the LED and avoid the maths side
of
things. I don't know the formulas off the top of my head so cannot help
with that at the moment.

Ian

Ian Bird
CibaVision UK Ltd.
Direct dial 01489 775570
Fax           01489
779570


                                                                                                                                
                     
"Frank
Mc                                                                                                 
                     
Alinden"                
To:      
<ukha_d@xxxxxxx>                                               
                     
<armagh@xxxxxxx       
cc:                                                                              
                     
om>                     
Subject:  Re: [ukha_d] Well.... we weren't
arrested....                          
                                                                                                                                
                     
17/09/02
13:49                                                                                            
                     
Please respond
to                                                                                         
                     
ukha_d                                                                                                    
                                                                                                                                
                                                                                                                                




Mark
        The Christmas tree light 
thingy correct , one out all out , Im
doing some garden lites (eventually) and im going to use 12v dc , i 
will
put 3 in series and use a resistor around 180 ohm ......  Maybe Ian
can put
something on his site???????

Frank

----- Original Message -----
From: "Mark Harrison" <Mark.Harrison@xxxxxxx>
To: <ukha_d@xxxxxxx>
Sent: Tuesday, September 17, 2002 10:28 PM
Subject: RE: [ukha_d] Well.... we weren't arrested....


> Frank,
>
> I believe you :-) I was asking to increase my own understanding...
>
> OK - next question, probably for Keiran... what value of resistor
and
power supply should I be using with the ones you sold me yesterday?
>
> M.
>
> -----Original Message-----
> From: Frank Mc Alinden [mailto:armagh@xxxxxxx]
> Sent: 17 September 2002 13:26
> To: ukha_d@xxxxxxx
> Subject: Re: [ukha_d] Well.... we weren't arrested....
>
>
> I cant remember the exact theory but one led tends to rob all the
current
> from memory, i think it might have something to do with the
voltage
> characterics of each led being slightly different ,but believe me
Mark
they
> need a seperate resistor .....
>
> Frank
> ----- Original Message -----
> From: "Mark Harrison" <Mark.Harrison@xxxxxxx>
> To: <ukha_d@xxxxxxx>
> Sent: Tuesday, September 17, 2002 10:21 PM
> Subject: RE: [ukha_d] Well.... we weren't arrested....
>
>
> > Frank,
> >
> > Why?
> >
> > Given that the resistor only serves to dump current, I'd assume
that I
> could have several LEDs in parallel with each other, then a
resistor
between
> that array and the -ve rail.
> >
> > Why won't this work?
> >
> > Mark
> >
> > -----Original Message-----
> > From: Frank Mc Alinden [mailto:armagh@xxxxxxx]
> > Sent: 17 September 2002 13:18
> > To: ukha_d@xxxxxxx
> > Subject: Re: [ukha_d] Well.... we weren't arrested....
> >
> >
> > Hi Mark
>
>            
If your wiring in parallel you must use a resistor for each
> led
> > ... remember the led link here it is
> > again............http://www.poptronics.com/interactive/index.html
> >
> > Frank Mc
> > ----- Original Message -----
> > From: "Mark Harrison" <Mark.Harrison@xxxxxxx>
> > To: <ukha_d@xxxxxxx>
> > Sent: Tuesday, September 17, 2002 10:14 PM
> > Subject: RE: [ukha_d] Well.... we weren't arrested....
> >
> >
> > > Funny you should mention that :-)
> > >
> > > I assume, BTW, that LEDs can be wired in parallel, so you
effectively
> > have:
> > >
> > > -----------------------------
> > >
> > > +ve rail
> > >
> > > LED  LED  LED  LED
> > >
> > > Resistor to dump the current
> > >
> > > -ve rail
> > >
> > > ------------------------------
> > >
> > >
> > > Does this sound right?
> > >
> > > M.
> > >
> > >
> > >
> > >
> > > -----Original Message-----
> > > From: Daniel James [mailto:daniel@xxxxxxx]
> > > Sent: 17 September 2002 13:11
> > > To: ukha_d@xxxxxxx
> > > Subject: RE: [ukha_d] Well.... we weren't arrested....
> > >
> > >
> > > Does this mean Mr Harrison is going to pick up a soldering
iron...
> > >
> > > .....only i'd like some notice first.... :-)
> > >
> > > -----Original Message-----
> > > From: Broadfoot, Kieran J
[mailto:Kieran.Broadfoot@xxxxxxx]
> > > Sent: 17 September 2002 13:07
> > > To: 'ukha_d@xxxxxxx'
> > > Subject: RE: [ukha_d] Well.... we weren't arrested....
> > >
> > >
> > >
> > > well it sure wasnt me ;-)
> > >
> > > next time you'll see me ill be standing on a street corner
with a
long
> > rain
> > > coat on saying: "here mate, wanna buy some leds"
;-)
> > >
> > > kieran
> > >
> > > -----Original Message-----
> > > From: Daniel James [mailto:daniel@xxxxxxx]
> > > Sent: Tuesday, September 17, 2002 1:05 PM
> > > To: ukha_d@xxxxxxx
> > > Subject: RE: [ukha_d] Well.... we weren't arrested....
> > >
> > >
> > > Were they your finest Caribbean gold ones then? :-)
> > >
> > > BTW who was the smartly dressed one :-P
> > >
> > > D
> > >
> > >
> > > http://www.automatedhome.co.uk
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