It will be great if someone can list me the components
Hi ashispostbox,
instead of PNP transistor in your figure I used an NPN transistor. Note that this one is a general purpose npn transistor. BC547.
Have a look at the circuit diagramView attachment 61927
when you turn on the main switch, which is the lamp power switch, the transformer converts the 230V ac to 12 V ac,which is rectified by the bridge rectifier circuit. The rectified voltage filtered by the capacitor....... and passed as a 12v dc voltage... ( with small ripples).the resistor Led combination just after that will indicate that power is ON.
Next section is the Controlling or Sensing Part.
Here, I used an LDR (light depended resistor) of negative type. that is when light falls on it the resistance is low. when no light falls on it, it resistance is high. Also a comparator (741) as a decision maker. Some resistors to help the decision maker (741) to take the decision I want. also a pot for adjusting the sensitivity.
Now let us have a study on its operation.
Note close the switch 2 (auto/manual switch) for auto mode
when the light falls on the LDR,its resistance low, so there won't be much voltage drop across LDR. so the rest of the voltage will drop across 2.2k resistor. there fore this voltage will be available to the inverting terminal of the op-amp(741). the voltage on the non-inverting terminal is made such as, during the light available state, voltage at non-inverting terminal is less than the voltage at inverting terminal. (it is done by adjusting the value of pot which determines the intensity). since in this condition , voltage at the inverting terminal is higher. so op-amp will give a 0v output. this won't turn on the NPN transistor. so the relay won't be active. Since the normally open terminal is connected to bulb, it won't ignite. thus the bulb wont light during day time.
Now when light is not there, the resistance of LDR will be much higher. thus most of the voltage will drop across LDR. very less voltage will be dropping across 2.2k. This will low voltage will be reaching the base of the inverting terminal. The voltage at the non-inverting terminal will be higher than this.( otherwise have to make-- only one time task) Since the voltage at +ve terminal is more, comparator will output a high (+12V). this will activate the transistor (relay driver) and the relay will be ON. this will cause the Bulb to turn ON. Thus bulb will be on during the low/no intensity of light
I said, you have to close the switch 2 for auto mode. Let us check what will happen if it is not closed or Manual mode is selected.
In this case there will be zero (0) V reaching to inverting terminal which represents the second case (no light case). thus the light will be on when the main switch (s1) is On and it will be OFF when Main switch is OFF.
Hope that this circuit and explanation is sufficient. In case of need, just ask... Have a good day/night...
I have two queries;
1. Any specific reason for using NPN transistor?
.
2. I was wondering if I can use an alternate to transformer as I want to make the circuit look sleek and less bulky.
Hi Ashish,
Answer 1. No. I just selected npn transistor according to the design. If I were to use Pnp, a small change is needed in the comparator circuit. Pnp transistor will be on when a low level is coming to the base. so we have to convert the logic of decision maker in such way.
Hope that this clears your doubt.
A lot more people is having this question. Answer is Yes... by the use of capacitive & resistive methods. More Information can be found from microchip's Application Note 954.
the link to it is given below.
https://ww1.microchip.com/downloads/en/AppNotes/00954A.pdf
Hope that this clears all your queries............. and is helpful.
First of all i would like to admire the OP that he is intretsed to build something. But not on his own. But he happened to open a commercial product manufactured by M/s Electro Expo Systems, Gurgaon India, and he posted the snaps of the PCB and others on his Flicker photo stream and too a copy and link here in EDA board. He just wanted a circuit diagram so that he can copy and produce it in a bulk (May be) but finding hard to trace the circuit due to his poor knowledge of electronics. . Despite we dont have cooked food with spoon feeding here the post was answered by "rjkrock" who rocked in every way and came out with a beautiful circuit just by looking the component side of the PCB. Really hats off to both. I would generously like the OP to post the results in the DIY section in coming days as too share his experiences and full project with all the details. Shall i expect?
Cheers
The discussion was about the commercial product getting duplicated with free support from innocent third party for getting the schematiccs and description without any royality to the Copyright owner. So its nice you came to know about the copyright owner and ready to pay some royality to him. Where the cow and the milk came in between?.My dear friend, to sell milk, you don't need to know how the cow produces the milk!
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