Hiya!

I'm making flashing white leds mounted to the ceiling of out sauna. There should be about 30 to 40 leds and in flashing groups of two (or three if possible). Duty cycle should be near 50% and the time between two flashes should be something like 2-3 seconds. Also I don't want the leds to flash between on and off, preferably like 50% brightness to full brightness, like flashing stars.

So far i have breadboarded few designs, one used only two alternating leds and with brightness going from 0 to 100, and the other only one led, but the fading cycle and brightness were what I'm looking for.

I guess this is what I'm looking for, but how can I make the brightness go as wanted. The cap value changes the rate so that shouldn't be the problem (right? ) Hopefully someone understood what I'm trying to make, so you can push me in the right direction

Thanks in advance!

 

You'd be well off to learn about PWM (pulse width modulation). This technique allows precise and efficient brightness control. Then you need to control the "program" applied to the PWM to give whatever brightness-vs-time scheme you want.

 

To achieve two step brightness, use a diode OR gate & two different current limiting resistor values, drive one leg with say a 555 [ full brightness] & other with straight 12V [ dim], or to reduce power consumption use a lower V for second leg and a common resistor per series string. Just about any diode would do , 1N400X, X= 2 to7., cheap & that is what I have with sufficient I rating.

 

Thanks for the replys! The latter option seems to suit me better, gotta try it out when I get my leds. Now I just gotta find the right sockets for an easy installation to the ceiling...

 

Take a look at the Arduino microcontroller platform. There are easy to use libraries that will let you PWM pins so you can control and easily change your pattern. The Arduino output pins would connect to transistors, that would control current to your string of LED's.

 

Arduino is pretty intriguing, greater control over parameters and all, but price of Arduino board is over 20e when simple 555 is more like 20 cents Do you think it is that much better option? And if it is, what is best model? I'm new to Arduino so it would take a while to learn the basics but I guess it might be worth it.

 

You wouldn't need a complete Arduino. The MCU in the Arduino, an Atmel Atmeg328, all by itself would be all you need. You can get them for about $5. You, need some way to program, but there are better ways to that than to dedicate an Arduino to the job. Like using a simple USB or Serial ICSP programmer. They too are only a few $. That way the programmer can be used for other projects.

 

I guess I'll try the 555 first, and then go for the Arduino later on, if needed. Thanks everyone for your replys!

 

Have you read this, Chapter 12 has several fading circuits.

LEDs, 555s, Flashers, and Light Chasers