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Electronics Forum / Basics / May 2006Freezing and Fading a led
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  SignatureKim..the man with a girls name, and Frankensteins body > 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 [quoted text clipped - 4 lines] > 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 >> 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 [quoted text clipped - 9 lines] >as well, and when the signal decreases, the only discharge path for the >cap is the LED and its current-limiting resistor. --- As usual, you're full of sh.t. Wanna know why? SignatureJohn Fields Professional Circuit Designer > >> 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 [quoted text clipped - 14 lines] > > Wanna know why? I know! I know! <hand waving in air> There's no 555 in it. >> >> If I have a LED driven from a electronic VU meter, is there a way to >have [quoted text clipped - 21 lines] > >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. SignatureJohn Fields Professional Circuit Designer ... > As usual, you're full of sh.t. > > Wanna know why? Easy- he's Rich, but Drunk... oh wait, it's just plain Rich... well it's all the same. 8oP Tim SignatureDeep Fryer: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms > On Wed, 24 May 2006 23:36:10 GMT, Rich Grise <richgrise@example.net> ... >>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 [quoted text clipped - 4 lines] > > Wanna know why? Because you're John Fields, and have a chip on your shoulder? Thanks, Rich >> On Wed, 24 May 2006 23:36:10 GMT, Rich Grise <richgrise@example.net> >... [quoted text clipped - 8 lines] > >Because you're John Fields, and have a chip on your shoulder? --- Nope. Whether I had a chip on my shoulder or not, you'd still be full of sh.t. Guess again? SignatureJohn Fields Professional Circuit Designer >>> On Wed, 24 May 2006 23:36:10 GMT, Rich Grise <richgrise@example.net> >>... [quoted text clipped - 12 lines] > Nope. Whether I had a chip on my shoulder or not, you'd still be > full of sh.t. Guess again? Optical Rectosis? ;-) >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? SignatureJohn Fields Professional Circuit Designer -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? [URL=http://www.theimagehosting.com][IMG]http://images6.theimagehosting.com/eyes6.gif[/IMG][/URL] >>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 [quoted text clipped - 11 lines] > > 2. Is one side of the VU meter connected to ground? >-I came across this schematic, although its supposed to fade incandescent >over a VERY long period of time. What do you think? >[URL=http://www.theimagehosting.com][IMG]http://images6.theimagehosting.com/eyes6.gif[/IMG][/URL] 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. 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. > -You are correct in my assessment of the needs > -Yes it is connected to ground on one side of the displays [quoted text clipped - 17 lines] >> >> 2. Is one side of the VU meter connected to ground? >>>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 [quoted text clipped - 17 lines] >over a VERY long period of time. What do you think? >[URL=http://www.theimagehosting.com][IMG]http://images6.theimagehosting.com/eyes6.gif[/IMG][/URL] --- 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. SignatureJohn Fields Professional Circuit Designer > 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 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. >> I came across this schematic, although its supposed to fade incandescent >> over a VERY long period of time. What do you think? [quoted text clipped - 9 lines] > Thanks, > -Bill > 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 came across this schematic, although its supposed to fade >> incandescent [quoted text clipped - 11 lines] > 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 > looked at your red eyes fading circuit and was wondering about the > reverse bias on the electrolytic cap. Is that OK to do indefinitely? Yes, it should be allright with 1 or 2 volts reverse. That circuit charges the cap backwards to about 1.5 volts. But if you are worried about it, you can use 2 larger caps back to back. Or, you might make it work using a non-polarized 2uF cap and somewhere around 1 meg in place of the 47K. Here's some data on electrolytic caps. http://electrochem.cwru.edu/ed/encycl/misc/c04-appguide.pdf -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? [quoted text clipped - 11 lines] > > -Bill Thanks Bill, I didn't know the back to back configuration. regards IanM Sorry, that's: http://server6.theimagehosting.com/image.php?img=eyes6.849.gif > 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 [quoted text clipped - 4 lines] > have a purpose. > Thanks in advance > Sorry, that's: > http://server6.theimagehosting.com/image.php?img=eyes6.849.gif Yes, it's ripped off from my website. Original is here: http://ourworld.compuserve.com/homepages/Bill_Bowden/page6.htm#eyes6.gif -Bill |
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