Reverse Color Organ

[Jon Jerpbak]

Using a light organ (Velleman MK114), I want a light to turn off to the music rather than turning on. This means the normal state of the light is on. I've tried using a NOT gate but the voltage coming out of the color organ is quite varied and the NOT gate is just on/off. I do not have access to an oscilloscope.
I'm looking for a device or circuit that will adjust the output voltage depending on the input voltage.
As an example:
Assume that the color organ out put voltage is anywhere between 0v and 9v.
If the input of this 'new' circuit is 0v, i want the output to be 9v.
If the input is 3v, i want the output to be 6v.
if the input is 9v, i want the output to be 0v.
I just need to be pointed in the right direction.
Thanks

 

[AnalogKid]

Please post the Velleman schematic. In the mean time, it sounds like you are asking about an analog inverter. Not the same as a digital not gate because in your case there is no implied reference to invert things about. An inverting opamp with an offset of Vcc/2 or 4.5 V will do what you describe. Whether or not it will work in your application is a different thing.

aka

 

[Jon Jerpbak]

Thanks for your answer, I'll start looking into your suggestions. I have attached the schematic

 

[Colin Mitchell]

Remove R2. Connect Pin4 of the opto coupler to the base of T1.

 

[Alec_t]

....and disconnect pin 4 of the opto coupler from ground.

 

[Jon Jerpbak]

That did the trick, working great.....thanks !!