Model Boat Mayhem

Technical, Techniques, Hints, and Tips => The "Black Arts!" ( Electrics & Electronics ) => Topic started by: david48 on November 07, 2016, 05:02:12 pm

Title: LED Calculator
Post by: david48 on November 07, 2016, 05:02:12 pm

 I found this web site ,some will know it .https://www.kitronik.co.uk/blog/led-resistor-value-calculator      .I am on with trying to make up a fibre optic board  for Fairmount Alpine .  If the long leg is + is the flat on the LED -   I could be wrong but I thought that if the legs are the same length the flat was + . The last batch I bought from Comp Shop ,the long leg is on the opposite side to the flat . Is it me !!!
Thank all for the help
David
Title: Re: LED Calculator
Post by: g6swj on November 07, 2016, 05:07:01 pm
From Sparkfun website...
The longer leg, should indicate the positive, anode pin. Or, if someoneís trimmed the legs, try finding the flat edge on the LEDís outer casing. The pin nearest the flat edge will be the negative, cathode pin.

Regards
Jonathan


Title: Re: LED Calculator
Post by: david48 on November 07, 2016, 05:13:02 pm

It was me ,just set up a warm white with 100ohm all looking good applied power PIFPAFPUF .I will try again 19 left .
thanks Jonathan
David
Title: Re: LED Calculator
Post by: NFMike on November 07, 2016, 05:55:02 pm
My way to remember is:
The long leg is because you need more to make a +
And the flat is a bit missing, or subtracted ... -

I expect there's a clever rhyme somewhere but I can never remember them.
Title: Re: LED Calculator
Post by: TheLongBuild on November 07, 2016, 06:02:27 pm
If using the correct voltage can you blow an led if you reverse the polarity ?, if not just exchange the wires until  it works..
Title: Re: LED Calculator
Post by: cos918 on November 07, 2016, 07:33:43 pm
It was me ,just set up a warm white with 100ohm all looking good applied power PIFPAFPUF .I will try again 19 left .
thanks Jonathan
David


What voltage are you using . for 12v I would go from 700 ohm to 1 k ohm


john
Title: Re: LED Calculator
Post by: Kipper on November 07, 2016, 11:28:36 pm
It was me ,just set up a warm white with 100ohm all looking good applied power PIFPAFPUF .I will try again 19 left .
thanks Jonathan
David

Using the calculator you referenced above, for 1 'warm white' 5mm LED, on a 12v battery, it gives a resistor of 470 ohm as the preferred value, so only using a 100 ohm resistor will cause it to go "PIFPAFPUF"  {-)

If only using 6v, you need a 150 ohm
 
Title: Re: LED Calculator
Post by: malcolmfrary on November 08, 2016, 08:26:21 am
LEDs have their forward voltage drop at a range of currents to give their glow.  They also have a maximum reverse voltage.  Exceeding either the forward current or the reverse voltage will kill them.
If uncertain as to which leg is which, connect two in reverse parallel, connect to a suitable voltage supply through a suitable resistor.  One will light.  That one is how they should be wired.  Since the forward voltage is always lower than the max reverse voltage, the one that didn't light up can be reconnected and reused.
Title: Re: LED Calculator
Post by: RAAArtyGunner on November 08, 2016, 09:14:38 am
LEDs have their forward voltage drop at a range of currents to give their glow.  They also have a maximum reverse voltage.  Exceeding either the forward current or the reverse voltage will kill them.
If uncertain as to which leg is which, connect two in reverse parallel, connect to a suitable voltage supply through a suitable resistor.  One will light.  That one is how they should be wired.  Since the forward voltage is always lower than the max reverse voltage, the one that didn't light up can be reconnected and reused.

Now that is a handy tip  O0  :-))
Title: Re: LED Calculator
Post by: david48 on November 08, 2016, 11:49:59 am

Thanks for the help and input gentlemen , it was me , No 1 I picked up the wrong resistor .No2 I failed to cut the track on the strip board where I had the resistor ,in effect track by passed the resistor ,a obvious over sight , I should have known better . Redid it all this morning all good now .
David