# PCB Heaven

## General Category => Your projects => Topic started by: Alex Robson on October 15, 2010, 07:12:53 AM

Title: another LED Dimmer type project
Post by: Alex Robson on October 15, 2010, 07:12:53 AM
Hi Everyone
I would like HELP in designing a circuit to dim each array of led  I have 10 white and 15 green and I have a 12VDC power  supply if that is suitable  White led rated 10000 m c d  20 m a
Green 12000 m c d  20 ma
I will be most grateful for your help with my project
Have a great day
arob2665
(p s) I'm new(Old kid) on the block so thank you for your time
Alex
Title: Re: another LED Dimmer type project
Post by: kam on October 16, 2010, 08:38:07 AM
You want to dim  LEDs with one dimmer, or 10 with one and 15 with the other?

In any case, this circuit i suppose fits you perfect:
An LED Array PWM Dimmer with the 555 (http://pcbheaven.com/circuitpages/LED_PWM_Dimmer/)
Title: Re: another LED Dimmer type project
Post by: Alex Robson on October 17, 2010, 04:36:25 AM
Hi K a m
Thank you for your circuit drawings  and not forgetting your Knowledge   The arrays are to be controlled separately a potentiometer for each array    Question    (1) Use your proposed circuit  for each  led array  I'm sorry for not making that clear (just an old retired engineer lacking in electronic know how
Alex
Title: Re: another LED Dimmer type project
Post by: kam on October 17, 2010, 11:26:01 AM
So, what you need, is 1 circuit for each array. For the 15 LEDs you should not have a problem at all. You make the circuit, and you make the LED array as per my circuit (in the same page) for the 12 volts. You need 5 rows, which will make 3x5 = 15 LEDs.

For the 10 LEDs there is a slight problem. You will make again the same circuit and again you will use the 12 volts array configuration with 3 rows, but that makes only 9 LEDs (3x3). To get the 10th LED running, you need to add one more row with greater resistor and just one LED. This resistor is calculated around 280 Ohms. You may need to increase slightly this value (eg 320 ohms) depending on the brightness that you get. Maybe this LED is brighter than the others. But this resistor (the 280 ohms) will have to dissipate a lot of power, around 250 mWatts, which means that you CANNOT use a normal 1/4 watt resistor. You need for this one to use an 1/2 watts, otherwise it will be toasted.

My suggestion -because you said that yo are not good with electronics- is to use 3 rows of 3 (9 LEDs) and light only 9 LEDs, OR use 4 rows of 3 and light 12 LEDs. If the 2 LEDs are a problem, just hide them...
Title: Re: another LED Dimmer type project
Post by: Alex Robson on October 18, 2010, 05:45:30 AM
Hi K a m
Thank you I'm most grateful  for your help and I do understand and  can add extra 2 led  with no problems  Now you have become my Hero
have a great day
Alex