In this post I have explained a simple ambient light dependent LED illumination controller circuit. The light fades or intensifies proportionately i response to the ambient light conditions. With brighter daylights, the LEd illumination gets softer and vice versa. The idea was requested by one of the dedicated members of this blog.
Technical Specifications
While seeking through the internet for a fully automated day/night LED Time Controller, I found your blog and I was wondering if you could help me with an advice. I want to add some kind of controller to give me smooth transition from sunrise/sunset of an aquarium LED lamp and with what I found on internet so far, seems way too complicated or just expensive for my goal.I was looking for something simple, without the need of simulating a thunderstorm through an Arduino board with n channels I will never use. I want something that could light up some LEDs at a given time while fading other LEDs, all with a smooth transition. And this has to repeat twice a day, every day.What do you say, can you help me?The lamp I have, is:12 x Cree XP-G2 R5 - 6500 - 7000K4 x Cree XP-G2 R2 - 2700 - 3200K2 x OSRAM SSL80 Hyper Red- for night time2x CREE XP-G R2All connected through 5 x KSQ 400mA (with the maximum of 6 LEDs in a row for each KSQ 400mA) to a laptop power adapter.Now, I don't know if my LEDs have dimming capability or I have to pass them through some dimmable drivers to obtain the desired effect.Also, the systems I found so far, are all based on a Arduino and they seem bulky. ex. Neptune (Apex), Profilux, Reef Keeper, DIM4So, that being said, thank you in advance for any help.
The Design
The shown light dependent led controller circuit is basically a light dependent PWM optimizer circuit whose duty cycle varies in accordance with the potential difference or level at its cotrol pinout.
As can be seen the circuit includes a couple 555 ICs. IC1 is configured as a standard astable having a frequency of around 80Hz. This frequency is not crucial in terms of the circuit functioning.
IC2 is configured as a PWM generator such that it compares the square wave signal at its pin2 and the triangle wave across its pin6/7.
This results in an output with a particular PWM content at pin#3 of ICs.
However this PWM duty cycle can be varied simply varying the potential difference at pin#5 of IC2.
An LDR can be seen attached across a potential divider preset at pin#5 of this IC. The preset can be used for fine tuning the results as desired.
The LDR resistance level now determines and varies the potential across this sensing pinout which in turn results in a proportionately varying duty cycle at pin#3.
The varying duty cycle causes the connected transistors to conduct accordingly and produce the correspondingly varying intensities over the connected LEDs.
The two transistors are configured as inverters which ensure opposite responses over the LED sets connected across the collector of the respective transistors.
Questions and Answers
Hello Mr. Swagatam, I love this idea and thank you for creating it. I would like to run this off a 35.5v power supply to run 63 leds, with a total draw of 126.65ma. I already figured the led arrangements and resistors and tested them with the supply, and it all works well. The led string voltages range between 20.5 and 35.2. I know the 555 can’t handle the 35v, can I just use a lm7812 or a lm317 to regulate the power to the 555 and have the collector/leds run off the 35.5v? Also can I use bc547’s instead of the Tip 122’s? As they are not drawing that much. I have tested with the 12volt supply with a few leds and got it working, but the leds connected to the first transistor don’t go out all the way. When I tested it using 1k resistors, they are drawing 3.92ma when on and .17ma when they are supposed to be off. I’m not sure why. I only have a 250k pot, could that be the problem? Thank you for your help.
Hello Jon, the set up which you have mentioned will work, but there are a few things which cannot be implemented as per your specifications:
1) BC547 cannot be used, instead you can try 2N2222 or 8050 transistor.
2) the pin#5 set up as shown may not be too efficient for the operations, therefore we may have to use a transistor stage here to increase the efficiency of the LDR, for this you may use a BC547 with its emitter connected with pin#5 of the IC2, base connected to the positive line through the LDR, and a 100K resistor connected between its base and the ground line. A 4k7 pot may be connected across pin#5 of IC2 and ground for controlling the sensitivity rate of the circuit.
To ensure complete shut off of the LEDs, you may connect a small value resistors across base emitter of the two driver transistors.