Eye bulb enlightner LED

Question

Hi to every body!

I'm new of this website and I have a favor to ask. I need to build a sort of table lamp with only 2 LED, a potentiometer to adjust the intensity of the light and a swich to turn on and off, everything powered by a 9V battery.

The only problem I don't know how calculate all the parts to built it and off course what kind of other material I need to made it, I have some basics in elettronis (really basic XD) I know how recognize the component I know how soldering, but thats it

Please if there is somebody that can help me I will be really happy

Ps sorry for my bad english....

shabaz · Answer

Hi Giuseppe, Check out this link: I Want to Do Electronics! Where do I start? Also there are circuits at talkingelectronics , if you hit ctrl-F and search for 'dimmer' you'll find an example. Its not as simple as just a potentiometer and an LED, it implements 'PWM' (which can be googled). But, you could (should) also experiment with LEDs and a pack of resistors, a 9V battery and a potentiometer, to see how things behave, it might suit your needs. You'll need these parts anyway even if you later decide you want to improve the circuit. For the formula, the LED wikipedia page is not bad, it will send you to a link with an LED circuit, which has some calculations.

D_Hersey · Answer

The problem with that, Guiseppe, is that the delta impedance of your LED around threshold is low and temperature dependent. So, a driver as you describe it would either not turn the LED on very well, or risk turning it on too much. Typically, only signal LEDs are energized through a resistor, because it is easy to waste lotsa power through the ballast resistor. So, the designers of high-power LED drivers with chopping schemes, much of the ballast R being replaced by L, which powers the LED during the no-supply-current interval. You can order dimmable LED drivers that are chopping and current-mode output. These will do what you want efficiently. Weber-Fechner states that for the perception of a stimulus to a biological system to seem to double in power, it must actually be squared. This is why volume pots on audio amps tend to be non-linear.

Eye bulb enlightner LED

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