Hi, I,m setting up a soundsystem in my room, and I wondering if there
was a way to set up some LED arrays to go with it.
here's the catch: I am limited to materials that can be gotten at any
radio repair place, as online purchases don't ship here. this means no
ICs.
is there any way of doing this?
my electronics skills are rather basic, but I want to fix that.
thanks,
Japa
Hi, Japa. You can make a simple LED driver with just a diode, a cap,
a few resistors and a darlington power transistor, if you've got a
spare DC wall wart that can power your LED array. This also assumes
you have current limiting resistors on the LEDs.
Here's how it would work (view in fixed font or M$ Notepad):
|
| .---o---o---o---o---o---o---o---o-------------.
| | | | | | | | | | |
| | | | | | | | | | |
| V~ V~ V~ V~ V~ V~ V~ V~ V~ |
| -~ -~ -~ -~ -~ -~ -~ -~ -~ |
| | | | | | | | | | |
| .-. .-. .-. .-. .-. .-. .-. .-. .-. |
| | | | | | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | | | | | | |
| '-' '-' '-' '-' '-' '-' '-' '-' '-' |
| | | | | | | | | | |
| | | | | | | | | | |
| | | | | | | | | | |
| '---o---o---o---o---o---o---o---o |
| | |
| |C |
| .---o |
| | | |
| 1N4002 ___ ___ B |/ | 12VDC ---
| o---->|---|___|--o----o-|___|--o-| | Wall -
| 1K | | 1K |> | Wart |
| +| .-. | |/ |
| To 10uF --- | |100K '-| |
| Speakers 25V --- | | |> |
| | '-' o |
| | | |E |
| o----------------o----o----------------o-------------'
|
|
(created by AACircuit v1.28.6 beta 04/19/05
www.tech-chat.de)
Use an NPN power darlington transistor like a TIP120 -- this will
easily switch half an amp or so, which should be more than enough for
a lot of LEDs. If you double (or triple or quadruple) up LEDs with
each current limiting resistor, you could literally drive a hundred
20mA LEDs with this setup.
Here's how it works: The diode keeps speaker voltage from reversing
and destroying the Darlington and cap. The 10uF cap charges up
through the first 1K resistor. When speaker voltage gets over 2V,
base current starts flowing through the second 1K resistor, the
darlington starts to conduct, and turns on the LEDs. The 100K
resistor acts a a bleeder to bring down the base voltage fairly
quickly (1/2 to a couple of seconds, depending on the speaker
voltage). If you feel the LEDs stay on too long or not long enough,
play with the value of the 100K resistor to change the decay time.
Be sure to put a good heatsink (5 watts or more) on the NPN darlington
-- at certain volume levels, it's gonna get hot and smoke unless it
has a way to dissipate the extra heat.
Inexpensive, easy, and all components are available at any radio
repair shop.
Good luck
Chris
This is .basics, where there is no such thing as a dumb
