LED Display Dimmer Circuit

[Tom Bombadil]

Hi I'm new to this forum (noob) am not at all qualified in the electronics field . I have built a display for my truck (27 volts) containing 307 5mm LEDs (204 Blue, 73 Yellow and 30 Red ) in a logo. I have found the display to be too bright and have been looking for a way to be able to vary the brightness of the whole display. I have seen some truck signs with a seperate box which has a knob which you can vary the brightness with. Does anyone know how I could make a variable dimmer ? I have tried connecting a small variable resistor along the positive supply but it was fried !
I was sent a "dimmer" which didnt do the job very well (not enough variance. I think it was meant for a display with less LEDs) and I have included all the diagrams I have used. If anyone can help me out at all I will be very grateful. Again I am not too electronic so forgive me if I ask for a diagram .Ive been stuck on this for months ! Thanx.

 

[Hero999]

There are several options:

1. Use a big series resistor to reduce the current.
2. Use a voltage regulator like th LM317 to reduce the voltage or limit the current.
3. Use a PWM controller to alter the duty cycle.

 

[ljcox]

The dimmer circuit is hopeless.
The pot is too high - 470 k in parallel with 220 Ohm will make little difference. And both ends should not be connected together.

But if you use a lower value pot, say 1000 Ohm, then it would have to be a high power wire wound type in order to dissipate the power.

Do you want to be able to vary the brightness with a pot or do you just want to reduce it permanently?

If the latter, then you could change all of the resistors for larger values.

If the former, then use either option 2 or 3 suggested by Hero999.