# LED flasher circuit

Discussion in 'LEDs and Optoelectronics' started by abramelin, Oct 21, 2010.

1. ### abramelin

2
0
Oct 20, 2010
Hello all
I'm in need of advice and/or a circuit diagram for the following.

One group of 6 LEDs to flash for one second on and off for one second.
Second group of 4 LEDs, to flash for .5 second on and off for .75 second.

Can it be built as one circuit or will it have to be two seperate circuits, I would perfer it as one if possible. I have built a circuit that flashes 2 LEDs that uses a 555 chip from what I've found online but I have no idea how to adapt it to do any or all of the above.

Cheers in advance for all help with this.

2. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,482
2,830
Jan 21, 2010
You need 2 555 oscillator circuits. One for the first flash rate, the second for the other.

A 555 can easily drive multiple LEDs. If these are high power LEDs, then it's not too hard to use a MOSFET or bipolar transistor driven by the 555 to switch them on and off.

I can't tell you exactly how to connect your LEDs as the best arrangement depends on your supply voltage. The simplest way is to place a resistor in series with each LED and then connect all of these between the 555's output ground.

Look at this page which shows how to connect multiple LEDs to a 555 for varying supply voltages.

edit: it could be 1 board with 2 555's on it, or 2 boards (each with 1 555), or a single board with a 556 (a dual 555) on it. As to whether you describe it as one circuit or 2, that's up to you.

Last edited: Oct 21, 2010
3. ### abramelin

2
0
Oct 20, 2010
Thanx for that.
Will give it a try.

4. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,482
2,830
Jan 21, 2010
Perhaps a little clarification is in order.

The link I gave you uses the discharge pin and a transistor to drive the LEDs. All I was intending to show was the way the LEDs are wired up. They can be connected to pin 3 (output).

Note that the 555 is typically limited in the duty cycle of the output. There are various methods that can be used to get around this limitation, the link I gave being one, but this probably being easier in your case as it allows the use of the output pin to drive the LEDs.