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Freezing and Fading a led

K

K `Sleep

Jan 1, 1970
0
If I have a LED driven from a electronic VU meter, is there a way to have
the led remain on (for approx 5 sec) when illuminated, then extinguish
slowly (over approx. a 5 sec.period).
So, in other words...when the led is illuminated by a audio level, it stays
on, then slowly fades off.
Like most of my requests, I know it sounds stupid...but it really does have
a purpose.
Thanks in advance
 
R

Rich Grise

Jan 1, 1970
0
If I have a LED driven from a electronic VU meter, is there a way to have
the led remain on (for approx 5 sec) when illuminated, then extinguish
slowly (over approx. a 5 sec.period).
So, in other words...when the led is illuminated by a audio level, it stays
on, then slowly fades off.
Like most of my requests, I know it sounds stupid...but it really does have
a purpose.
Thanks in advance

Sure - a capacitor and a diode. It would be a rudimentary peak detector -
the diode allows the current that lights the LED to charge the capacitor
as well, and when the signal decreases, the only discharge path for the
cap is the LED and its current-limiting resistor.

Good Luck!
Rich
 
J

John Fields

Jan 1, 1970
0
If I have a LED driven from a electronic VU meter, is there a way to have
the led remain on (for approx 5 sec) when illuminated, then extinguish
slowly (over approx. a 5 sec.period).
So, in other words...when the led is illuminated by a audio level, it stays
on, then slowly fades off.

---
1. From your post, I assume that you want the LED to stay fully
illuminated while the VU meter is indicating audio and then,
when there is no audio, you want the LED to stay illuminated
for 5 seconds and then to fade to black in another 5 seconds.
Is that right?

2. Is one side of the VU meter connected to ground?
 
J

John Fields

Jan 1, 1970
0
Sure - a capacitor and a diode. It would be a rudimentary peak detector -
the diode allows the current that lights the LED to charge the capacitor
as well, and when the signal decreases, the only discharge path for the
cap is the LED and its current-limiting resistor.
 
K

K `Sleep

Jan 1, 1970
0
-You are correct in my assessment of the needs
-Yes it is connected to ground on one side of the displays
-I came across this schematic, although its supposed to fade incandescent
over a VERY long period of time. What do you think?
 
R

Richard Henry

Jan 1, 1970
0
I know! I know! <hand waving in air>

There's no 555 in it.
 
D

default

Jan 1, 1970
0
-I came across this schematic, although its supposed to fade incandescent
over a VERY long period of time. What do you think?

Looks like it is designed to flash a lamp on and off for a period of
time . . . just from looking at the schematic - I could be wrong. Do
you intend to build one of these circuits for each led in the display?

Peak and Hold . . . that sort of thing is usually designed into the
chip - it is a hassle to build it from discrete analog parts.

Peak and Hold is in the books - - - take that circuit and have it
pulse the bargraph display circuit with the peak and hold voltage? 50%
of the time the bargraph display follows the signal, the other 50% it
displays the (current/real time) peak voltage. Continuously switching
between the two levels. Your eyes will see the bargraph moving and
the peaks will stay illuminated longer.

As far as a cheap and dirty cap and diode . . . I don't think so. Each
LED would have the circuit and each led would stay illuminated once it
was turned on.

Peak and Hold - and multiplex the signal input to the bargraph display
circuitry - that could be made to work.
 
T

Tim Williams

Jan 1, 1970
0
John Fields said:
....
As usual, you're full of shit.

Wanna know why?

Easy- he's Rich, but Drunk...
oh wait, it's just plain Rich... well it's all the same. 8oP

Tim
 
J

John Fields

Jan 1, 1970
0
I know! I know! <hand waving in air>

There's no 555 in it.

---
Nuh-uh... It's threefold.

1st fold, you won't be able to get the response the OP wants with a
simple diode-cap intregrator,

2nd fold, there won't be enough power coming into the VU from the
audio signal to make the circuit work.

3rd fold, the circuit will screw up the response of the VU meter.
 
O

Oppie

Jan 1, 1970
0
The link you pointed to is a basic PWM control.
LM324 sections 1 and 7 generate a triangle wave which is presented to
amplifier section 14 used as a comparator. The 3300uF cap is initially
discharged and will cause a nearly 100% duty cycle to drive the lamps. As
the capacitor charges, its voltage compared against the sawtooth causes the
PWM to decrease to zero (lamps dimmed to black).

May I recommend that when you post a link, don't put it in brackets. Also
leave a space after the link. This allows readers to auto detect a link.

K `Sleep said:
-You are correct in my assessment of the needs
-Yes it is connected to ground on one side of the displays
-I came across this schematic, although its supposed to fade incandescent
over a VERY long period of time. What do you think?
 
R

Rich Grise

Jan 1, 1970
0
As usual, you're full of shit.

Wanna know why?

Because you're John Fields, and have a chip on your shoulder?

Thanks,
Rich
 
J

John Fields

Jan 1, 1970
0
John Fields said:
---
1. From your post, I assume that you want the LED to stay fully
illuminated while the VU meter is indicating audio and then,
when there is no audio, you want the LED to stay illuminated
for 5 seconds and then to fade to black in another 5 seconds.
Is that right?

2. Is one side of the VU meter connected to ground?
-You are correct in my assessment of the needs
-Yes it is connected to ground on one side of the displays
-I came across this schematic, although its supposed to fade incandescent
over a VERY long period of time. What do you think?

---
Please bottom post.

I think this will work for you: (view in Courier)

+12V>---------+--------------+-----+-------+--------------+
| | | | |
| | | | [510]
[10K] [1M] | | |A
| | | | [LED]
| +--[10M]--+ |R2 | |
|R1 | | [10K]<---|-\ E
[10K]<-+-|+\ | | | >-+-[10K]--B 2N3906
| | >----+-----|------|+/ | C
IN>--[100K]---|------|-/U1A | | U1B| |+ |
| LM393 |+ | | [22µF] |
| [10µF] | | |C2 |
| | | | | |
GND>----------+--------------+-----+-------+---+----------+

Adjust R1 to determine at what input voltage the circuit triggers
ON, adjust R2 to set the delay before dimming starts and select C2
to give you the dimming timeout you want. Wth 22µF the LED current
goes from 20mA to 2mA in about 5 seconds.
 
K

K `Sleep

Jan 1, 1970
0
Don't you think that "ripped off' is a bit of a strong statement.
If a circuit is made available for the world to see, and therefore used as
an example (as is the case is here) is that ripping it off?
Kind of a old....and outdated way of thinking of things...isn't it.
By the way....I have to say that Bill Bowdens schematics circuits page is
well designed, and quite useful. I often refer to it.

Bill Bowden said:
I came across this schematic, although its supposed to fade incandescent
over a VERY long period of time. What do you think?
http://images6.theimagehosting.com/eyes6.gif[/IMG][/URL]

I think it was ripped off my website at:

http://ourworld.compuserve.com/homepages/Bill_Bowden/page6.htm#eyes6.gif

You will get more information there with several alernatives using both
LEDs or incandescents.

Thanks,
-Bill
 
B

Bill Bowden

Jan 1, 1970
0
Don't you think that "ripped off' is a bit of a strong statement.

No.
If a circuit is made available for the world to see, and therefore used
as an example (as is the case is here) is that ripping it off?

Yes, and it's not an example. It's a unique work of art that belongs to
the author, and anybody that copies and reposts it somewhere else
without permission is a thief.

-Bill
 
I

IanM

Jan 1, 1970
0
Bill Bowden said:
I came across this schematic, although its supposed to fade
incandescent
over a VERY long period of time. What do you think?
http://images6.theimagehosting.com/eyes6.gif[/IMG][/URL]

I think it was ripped off my website at:

http://ourworld.compuserve.com/homepages/Bill_Bowden/page6.htm#eyes6.gif

You will get more information there with several alernatives using
both
LEDs or incandescents.

Thanks,
-Bill
Hi Bill,

looked at your red eyes fading circuit and was wondering about the
reverse
bias on the electrolytic cap. Is that OK to do indefinitely?

regards

IanM
 
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