light organ circuit issues... - Page 1
Forum section: electronics / projects

author: connorwk
author_rank: Contributor
timestamp: April 21, 2013, 03:46:39 am
content: I'm setting up a light organ (making lights flash to music) in my car...I've found these simple circuits online that use tip-31 transistors.There is a very crude diagram in the attachments.Sorry about the crudeness its almost midnight here and I'm a bit lazy...Anyway I noticed right after attaching it and turning on the power in the car I got static and the lights didn't flash they just stayed dim...I'm assuming its because of mixing the car's main ground and the isolated ground of the sound system...I'm wondering if there is a better circuit for my situation...I've looked around the web but I've only overly advance circuits for what I'd like to do or idiots hooking 3v leds directly to a sub-woofer.I have 12v strip leds that I'm using and a DPDT ON-OFF-ON switch.I'd really appreciate help with this.

author: Rerouter
author_rank: Super Contributor
timestamp: April 21, 2013, 03:59:55 am
content: you have probably blown to buggery your transistors,you will want atleast a 100 ohm resistor between right + / left + and your transistor bases, otherwise that transistor acts like a diode shunting your signal to ground the moment it increases more than 0.7V, and as it only required 1A being shunted like that to damage it i would say replace them, add the resistors and see how it goes,

author: connorwk
author_rank: Contributor
timestamp: April 21, 2013, 04:03:41 am
content: You know I was afraid of that...Good thing I have more transistors...Thanks I'll give it a try!

author: connorwk
author_rank: Contributor
timestamp: April 21, 2013, 04:20:20 am
content: Oh also do you think adding that resistor and working transistors will fix the static problems?

author: Rerouter
author_rank: Super Contributor
timestamp: April 21, 2013, 05:04:27 am
content: that static your hearing is likely the output of your raido / amplifier being shunted on positive signals, and possibly also on negative with breakdowns as the base doesnt like negative voltages bigger than say 5V (may want to add a protection diode from ground to each base)another thing i cannot help but notice is that is will likely not give you the effect you desire, this will turn the lights on every time the signal exceeds 0.7V, so for a standard voice / music tone of about 1Khz, your just going to see solid lights at something less than half brightness most of the time, what i presume those other "more complex" circuits use is a peak and hold circuit tied in with a comparator, e.g. thishttp://bit.ly/ZGCsN0

author: connorwk
author_rank: Contributor
timestamp: April 21, 2013, 05:52:02 am
content: Would I place the diode like...base -->|-- groundorbase --|<-- groundI think you'd do it the second way... no?Also yes that is the type of circuit I was previously talking about I understand how they work but I don't think I have the parts and I don't feel like goin through the 30 scrap boards I have lookin for the parts to use...I was hoping to get it working with what I have at the moment, if not I'll have to go order other parts...Sorry for so many questions just don't want to blow another set of transistors or have to remove it again and redo the circuit.I hope adding the resistor and diode will help the static... If not will adding capacitors somewhere help?Thanks for all this help by the way

author: Rerouter
author_rank: Super Contributor
timestamp: April 21, 2013, 06:04:12 am
content: the second,capacitance will not do anything for static, its likely coming from your audio source, try grounding the input if you want your best hope and getting it quiet,

author: connorwk
author_rank: Contributor
timestamp: April 21, 2013, 06:10:03 am
content: Ok thanks I'll make the board up right away and test it asap!

author: jahonen
author_rank: Super Contributor
timestamp: April 21, 2013, 07:35:23 am
content: Also note that you can't connect this kind of circuit to an amplifier with bridged outputs (most car audio stuff has bridged output) as left- and right- are wired together, but they are driven independently by the amplifier. You are risking blowing up your amplifiers output stages.Regards,Janne

author: amyk
author_rank: Super Contributor
timestamp: April 21, 2013, 09:11:31 am
content: Quote from: connorwk on April 21, 2013, 03:46:39 amThe circuit you found isn't any better... if you can go find the author of it, be sure to tell him that he appears to have no understanding of how transistors work.(Actually it would be OK to not have a base resistor when in emitter follower mode, but I doubt whoever made that circuit would know...)

author: connorwk
author_rank: Contributor
timestamp: April 21, 2013, 06:38:51 pm
content: Yea I tried it... Still gave me static to the speakers while it was hooked upI wish I'd have a better understanding of electronics myself but as of now being 16 I'm still learning...If anyone has suggestive circuits for my situation I'd love to see them and I can order the parts from digi-key.I have the positives of the leds hooked up to 12v in the car and the ground going to the center of a DPDT switch one side of the switch goes straight to ground and the other go to two free wires one for left leds one for right I also have the left+ left- and right+ right- coming from the stereo also two free ground wires.So I have these wires available to hook to a circuit: | left+ | left- | right+ | right- | Gnd | Gnd | Led gnd left | Led gnd right |I hope that makes sense...(I'm getting the 12v for the leds and the Gnd from the back side of a cigarette lighter plug so its got a 10-14v range which the leds are tolerant with but I think is was is causing the static on the speakers)Thanks for all the help!