One hundred and one LED''s
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Posts: 46,084
The voltage drop across an LED is typically 1.2 to 1.4 volts, so you may
really need to have 25 parallel connections of 4 LEDs in series (6 volts - 4
*1.4 gives about .4 v headroom). The resistor in series with an LED is used
to reduce the amount of current passing through it to prevent damaging the
LED. Typically 330 ohms is used from a 5 volt source, so you could guess
that an LED is ok in the range of (5-1.4)/330 or around 10 to 15 mA. You can
reverse this and figure the intrinsic resistance of the LED itself is
1.4/0.010 or 100 to 150 ohms. So if you have 4 of these hooked in series
with a 6 volt source, the current through each would be 6/(4*100) or about
10 to 15 mA, just where you started with the resistor/single LED combo. So
you should be just fine hooking the LEDs 4 in a series across a 6 volt power
source with no resistor. But if you look at current requirements, you've got
25 strings of LEDs times 15 mA giving you 375 mA, pretty good draw from the
battery. And some LEDs like a little more current, maybe 25 mA to burn
brighter. Hope ya got a rechargable battery. If you want more in series, use
a higher voltage battery. To get all 100 in series would require a 140 v or
so battery. Simplest method of control might be using a stamp pin to acuate
a relay to simply power on and off the whole thing. Remember the stamp's
current limits.
Original Message
From: "Bruce Bates" <bvbates@u...>
To: <basicstamps@egroups.com>
Sent: Saturday, November 18, 2000 2:32 PM
Subject: Re: [noparse][[/noparse]basicstamps] One hundred and one LED's
> At 03:18 PM 11/18/2000 -0500, you wrote:
>
> > Hello everyone,
> > I've been given a task which requires lighting approx.
> >100 LED's from a large 6V battery. Although the circuit will be
controlled
> >by a micro, I just need to switch them all on and all off. My question
is:
> >Is there some way I can wire them in series (to simplify hand wiring
them)
> >that will avoid the use of current limiting resistors? ie. can I use the
> >LEDs themselves to drop the voltage...I'm trying to avoid a one
> >resistor/LED scenario and I don't want a circuit that has 100 parallel
> >connections...
> >
> >Best regards, Duncan
> Hi Duncan -
>
> Sure, why not - that's how Christmas tree lamps worked in years gone by.
Just remember the voltage drop through each one, and if one dies, they all
die. Today the newer ones are wired in series-parallel or have internal
resistors - least the one's I've seen.
>
> Have fun ! I DON'T envy you : )
>
> Bruce Bates
>
>
>
>
>
>
really need to have 25 parallel connections of 4 LEDs in series (6 volts - 4
*1.4 gives about .4 v headroom). The resistor in series with an LED is used
to reduce the amount of current passing through it to prevent damaging the
LED. Typically 330 ohms is used from a 5 volt source, so you could guess
that an LED is ok in the range of (5-1.4)/330 or around 10 to 15 mA. You can
reverse this and figure the intrinsic resistance of the LED itself is
1.4/0.010 or 100 to 150 ohms. So if you have 4 of these hooked in series
with a 6 volt source, the current through each would be 6/(4*100) or about
10 to 15 mA, just where you started with the resistor/single LED combo. So
you should be just fine hooking the LEDs 4 in a series across a 6 volt power
source with no resistor. But if you look at current requirements, you've got
25 strings of LEDs times 15 mA giving you 375 mA, pretty good draw from the
battery. And some LEDs like a little more current, maybe 25 mA to burn
brighter. Hope ya got a rechargable battery. If you want more in series, use
a higher voltage battery. To get all 100 in series would require a 140 v or
so battery. Simplest method of control might be using a stamp pin to acuate
a relay to simply power on and off the whole thing. Remember the stamp's
current limits.
Original Message
From: "Bruce Bates" <bvbates@u...>
To: <basicstamps@egroups.com>
Sent: Saturday, November 18, 2000 2:32 PM
Subject: Re: [noparse][[/noparse]basicstamps] One hundred and one LED's
> At 03:18 PM 11/18/2000 -0500, you wrote:
>
> > Hello everyone,
> > I've been given a task which requires lighting approx.
> >100 LED's from a large 6V battery. Although the circuit will be
controlled
> >by a micro, I just need to switch them all on and all off. My question
is:
> >Is there some way I can wire them in series (to simplify hand wiring
them)
> >that will avoid the use of current limiting resistors? ie. can I use the
> >LEDs themselves to drop the voltage...I'm trying to avoid a one
> >resistor/LED scenario and I don't want a circuit that has 100 parallel
> >connections...
> >
> >Best regards, Duncan
> Hi Duncan -
>
> Sure, why not - that's how Christmas tree lamps worked in years gone by.
Just remember the voltage drop through each one, and if one dies, they all
die. Today the newer ones are wired in series-parallel or have internal
resistors - least the one's I've seen.
>
> Have fun ! I DON'T envy you : )
>
> Bruce Bates
>
>
>
>
>
>