Re: LED's for dummies
- From: ehsjr <ehsjr@xxxxxxxxxxxxxxxx>
- Date: Sun, 20 Aug 2006 05:23:22 GMT
hepstyle@xxxxxxxxx wrote:
I'm apparently an incredible dummy, because I can't wrap my mind around
this concept yet. So I'm sorry to ask such a rudimentary set of
questions.
I have been given a bowling pin. I am supposed to take this bowling
pina dn turn it into a work of art which will be auctioned off for a
local charity. My idea as a budding electronics hobbyist is to
basically decoupage the pin and then install a bunch of LED's driven by
a wall wart.
So I will cut the pin in half at its widest point and hollow out the
inside as much as I can so that the electronics will fit in there, then
I will drill holes or wiring and try to place the LEDs in little
recesses that I will create.
ANYWAY, I will be using 18-24 LEDs of various colors. Here is a list
(i'd be using 3-4 of each color):
Blue - 3.6V, 20mA
Orange - 1.7V, 20mA
Amber - 1.7V, 20mA
Green - 3.3V, 20mA
Red - 2.3V, 20mA
Sea Green - 3.3V, 20mA
My first problem is that I don't know for sure if those voltage specs
are just the voltage required to power the diode or if it is a
measurement of the voltage drop, or even if there is a difference
between the two.
But since the current for all of them is the same, I considered wiring
them in series. The problem there is that I was hoping to use a 9V,
500mA wall wart that I already have, and if those voltages are voltage
drops, I can't wire too many at a time.
So clearly I have to use a combination of parallel and series circuits
in order to control the current while keeping the voltage under, say
7.2 volts. And I know that I will have to incorporate resistors
somewhere along the line. But that's it. I can't make it to the next
step. I'm not sure how I should distribute the LEDs so as to create
the most efficient circuit. I'm not sure where to put the resistors.
I want to draw a wiring diagram, of course, but I can't visualize this
for some reason.
If anyone can point me in the right direction here, I'd really
appreciate it. I'm not looking for someone to bail me out as much as I
need someone to show me what my mental obstacle is, maybe helpe me get
past it. Thanks in advance for any help you can share!
Just to give you another option:
Create 3 or 4 strings of LEDs in series, using
1 of each color led you have. Use a 24 volt
wall wart such as DCTX-2460 from Allelectronics
http://www.allelectronics.com/
Add an LM317 and two resistors (3.6K & 240 ohms)and a
capacitor to provide a regulated 20 volts output, and
use a 56 ohm resistor in series with each string.
Option 2 is probably best:
..------. -----
| +|----+--Vin|LM317|Vout---+----+------+------+
| | | ----- | | | |
| 24V | | Adj | [LEDs] [LEDs] [LEDs]
| DC | | | | | | |
| | [.1uF] +--[240R]--+ | | |
| Wall | | | [56R] [56R] [56R]
| Wart | | [3.6K] | | |
| | | | | | |
| -|----+--------+---------------+------+------+
..------.
Voltage at the Vout pin will be 20.0
Each string of LEDs has a nominal Vf of ~18.9 volts.
The 56 ohm resistor will limit the current through
the string to ~19.6 mA
Ed
.
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