This blinking LED circuit uses only one IC, requires no firmware, and can be modified almost without limit.  It is an excellent starting circuit for those wanting to create blinking LED effects.  With proper changes to the current-limiting resistors, this circuit can run on 3 - 15 VDC, making it ideal for battery-powered operation.

I cannot find the original page that started me using this circuit.  That page contained an excellent explanation of how this circuit works and included info on determining blink rates and patterns.  You can find some of that information here, but it's still not as good as the original page...

Refer to my Eagle schematic (PDF) here.  This circuit uses a single 4060B IC, which is a CMOS 14-stage binary divider.  Note that the 'B' is important; the 4060B device has extra current capability, needed for driving the LEDs.  Refer to the Fairchild 4060 datasheet here.

Basically, R1, R2, and C2 form an oscillator, generating timing pulses for the 4060.  These pulses feed the 4060's internal chain of dividers.  The output of each divider is available on one of the Qn pins.  For example, the Q4 output (pin 7) is the output from the 4th divider and changes state at the original clock frequency divided by 2^4 or 16.

Each Q output is at either GND or VCC at any given moment, and the outputs change between these states based on the oscillator frequency and which output they are in the divider chain.

If you choose any two Q outputs, such as Q4 and Q6 in the schematic, you will see that these two outputs can provide three different ways to control an LED:

Q4	Q6	LED control
GND	GND	LED is off
GND	VCC	LED conducts from Q6 to Q4 (LED2 lights)
VCC	GND	LED conducts from Q4 to Q6 (LED1 lights)
VCC	VCC	LED is off

Because the LEDs are reverse-wired between the two outputs, you will never have both of these LEDs on at the same time.

Now take this simple two-LED concept and start adding LEDs and current-limiting resistors between other outputs.  The behavior of any one LED depends on the direction it is wired between outputs, the original oscillator frequency, and the outputs you use.

I have had 40 LEDs of various colors wired to a single 4060 IC and the resulting pattern is simply beautiful!  Note that it can take many minutes for the pattern to repeat; unless you have a very long attention span, the pattern will look random to you.

Experiment with different colored LEDs in your design.  For example, you could use a red LED1 and a green LED2.

The LED brightness will be a function of the voltage you provide and the value of the current-limiting resistor (R3).  The value of 180 ohms shown here should work for most LEDs using a voltage of 3 to 6 VDC.  LED brightness is also a function of the LEDs you use; try to get some of the high-brightness devices to get more punch for your volts.


What current-limiting resistor?
The picture above shows a version of this circuit I built to run on 12 VDC.  Here I used a string of LEDs in place of the single LED1 or LED2.  The trick is to add the forward voltages of the LEDs in the string, trying to get as close to 12 VDC total as possible.  For example, the forward voltage of red LEDs is 2 VDC, so I used a string of six red LEDs in place of LED1 or LED2.  Similarly, I used strings of four blue, four green, or five yellow LEDs.  Since the total forward voltage for each string is nearly equal to the power supply I used, I simply eliminated the current-limiting resistor and wired the series strings directly to the two outputs I chose.


Home