The post details a simple fading LED light effect generator circuit which can be set for operating in fish aquariums in the prescribed manner for a predetermined length of time. The idea was requested by Mr. Jaco.

Technical Specifications

My name is Jaco and I am from sunny South Africa. I have an aquarium that I want to "modify" the lights on. I would like a circuit based on a cd4060 chip that can bring multiple strings of LED's from power off to max brightness and the reverse over a period of 8 - 12 hours.

I'm going to use set times to explain what I would want to happen. The actual timing will obviously not be that perfect. But here goes.

My basic idea - at 6am the circuit should start lighting up slowly to max brightness until 11am.

It should then stay on max brightness until 1pm.

Then slowly dim from max brightness to off at 5pm.

It should stay off until 7am the next morning when the cycle restarts. An arduino circuit will unfortunately not work for me, as I cannot get my hands on one.

Thank you in advance.

The Design

The requested fading LED light circuit for illuminating fish aquariums can be visualized in the above diagram.

I have used a 555 IC by mistake for generating the delay time interval, however a 4060 IC based circuit may be also effectively used in place of the IC 555 stage, in fact a 4060 circuit would be able to produce a 10 times bigger delay effect reliably, than the IC 555 counterpart.

The time interval oscillator section which is formed by the IC 555 produces the required sequence pulses for the attached 4017 IC which is a Johnson decade counter and divide by 10 IC. It becomes responsible for creating a shifting high logic across the shown 10 output starting from pin#3 to pin#11.

Meaning with every pulse generated from the IC 555 pin#3 at pin#14 of 4017 will cause the supply voltage to shift from its pin#3 (start pin) to the subsequent pinouts (2, 4, 7...etc), this implies that if the delay time between each pulse from the IC 555 is say 1/2 an hour, this would cause the high logic from pin#3 to pin#11 of the IC 4017 to consume around 1/2 x 10 = 5 hours.

The outputs of the IC 4017 can eb seen configured with a emitter follower transistor circuit formed around TIP122 which is a Darlington transistor and thus features a high current response across its base and emitter pinouts.

Since it's configured as an emitter follower ( or as a common collector), it ensures the generation of a precisely identical (almost) voltage across the load, connected at its emitter/ground, equivalent to the voltage applied at its base. It Implies that if the voltage at its base is 3V, then the voltage at its emitter would be around 2.4V (the 0.6V drop is inherent and cannot be avoided).

Similarly if the voltage at the base of the TIP122 is 6V, this will be interpreted as a 5.4V across its emitter...and so on.

This is the reason why the configuration is named "emitter follower", meaning an "emitter" lead which follows the base lead voltage of the transistor.

We can see an array of resistors connected across the pinouts of the 4017 IC which in turn is attached with the base of the TIP122 transistor, in conjunction with a 10k preset across the base and ground of the transistor.

These resistors across the 4017 outputs are arranged in an incremental value, such that it corresponds with the set 10k preset value and forms a potential divider network.

The voltage developed at the junction (base of the transistor) of this potential divider in response to the sequencing high across the relevant pinouts of the IC can be expected to be in an increasing order.

This incrementing potential difference order can be assigned across a few outputs of the IC 4017, say up to pin#4.

So the TIP122 can be assumed to respond to these incrementing potentials and produce an equivalently incrementing voltage at its emitter pin, which in turn makes sure that the connected LEDs go through a gentle reverse fading effect and become brighter slowly.

The 1000uF capacitor connected in parallel to the preset further aids to the effect and causes the above reverse fading to happen at a slow and a gradual manner.

Once the sequence reaches pin#7 and subsequently to pin#10, 1 and 5, these pinouts resistors can be selected such that a maximum voltage is generated at the base of the transistor with reference to the preset value.

This in turn enables the LEDs to stay illuminated at the maximum brightness, until the sequence has crossed these pinouts and reached pin#6, and subsequently to pin#9, 10 and pin#11.

The resistors in these pinouts may be fixed in a demoting fashion such that the potential difference generated at the base of the transistor goes through a falling potential level, which in turn is induced over the LEDs for generating a nice and slow fading effect.

The 1000uF capacitor at this point now acts in a reverse manner, and allows the fading to take place rather slowly, until the LEds are finally shut off as the sequence reaches the pin#11 of the IC4017.

After this the operation reverts to pin#3 and the cycle repeats as explained in the above discussion.


In the above design I seemed to have missed the 24 hour resetting stage in the circuit, the following new improved version of the fading LED light timer circuit takes care of this feature and operates the LEDs exactly as per the mentioned request.

Adding 24 Hour Resetting Feature

Here the IC 4060 is used as a timer oscillator whose pin#15 is used for generating a relatively faster frequency for the IC2, such that the outputs of IC2 are able to genearte the required slow glow and slow fade sequencing effect on the LED driver transistor within 12 hour period.

On the other hand pin#3 of the IC 4060 which geneartes around 7 to 8 times slower frequency than pin #15 clocks IC3 appropriately, and this inclusion becomes responsible for the 24 hour resetting feature in this new circuit.

Pin#15 and pin#3 are arbritarily chosen here with an assumption that pin#15 would enable the LEDs to operate for 12 hours, while pin#3 pulse rate will reset the IC1 after every 24 hours via IC3.

This timing will need to be tested with some trial and error using the available extensive range option that IC1 and IC3 are able to provide through their 10nos of output pins, and these may be experimented for getting the most favarable timing range across both the features, that is for 12 hour LED effect and for the 24 hour reset.

Also do not forget the P1 adjustment which further adds to the adjustment range of the design.

Parts List

R1 = 2M2,
R2, R3 = 100K,
P1 = 1M pot
C1 = 1uF
C2 = 0.22uF
R4--R8 = value in decreasing sequence (needs to be calculated with respect to the 10k preset setting)
R8--R13= value in increasing sequence (needs to be calculated with respect to the 10k preset setting)

all diodes = 1N4148

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