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    Twilight Switch component and circuit help

    Hi, I am a new bee and I got interested into DIY for a twilight circuit. It will be great if someone can list me the components and the circuit diagram so that I can make one :-)


    Link to all 17 images: Twilight switch DIY - a set on Flickr

    Regards,
    Ashish

    •   Alt22nd September 2011, 04:40

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    Re: Twilight Switch component and circuit help

    It will be great if someone can list me the components
    so as a first step I will list the components

    1. 230V to 0-12V step down Transformer
    2.4 1N4007(1N4001) diodes for bridge rectifier
    3.1 free wheeling diode for protecting from relay sparks-- 1N4007
    4. 1 more diode --- 1N4007 for ensuring unidirectional flow ( actually No need, or i don't understand with the first look,,, It is most probably they implemented for coupling)
    5.two capacitors for filtering (1000uF,10uF)
    6. Resistors (10K, 2.2K, 1K x3,4.7K) for limiting the current flow and setting the threshold
    7.switches Manual/auto-selection , Main Switch, both are SPST ( Single Pole Single Throw)
    8. 22k pot as a threshold/sensitivity adjuster.
    9. CK 100 ( analogous to SK100, PNP Transistor), driving the rely.
    10.LDR(Light Dependent Resistor) as a light sensor.
    11. Op amp IC 741, for comparing the light availability state and non-availability state..
    12. then Connector for connecting the to the mains........... and also to the lamp
    13. sure there are LEDs for displaying the status (mains on, relay on)
    14. connecting wires
    15.Rely (12V dc) for switch on the lamp after getting the signal from opamp
    16. also Jumper pin( actually we had to use a preset pot for that, but don't worry)
    17. 8 pin IC base & breadboard ( or PCB)

    Hope that I covered almost all the parts. don't know anything left. but if left just notify me......... I will provide you with a rough schematic after some time. but before that try to do some schematic work by yourself......... even if i provide the schematic, you will have to work on it a little, otherwise, you won't be learning it......k... are you ready for that???

    If yes, you can expect it at tomorrow...........



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    Re: Twilight Switch component and circuit help

    Thank you for the list. I agree and appreciate with you for my learning curve. :-P



    •   Alt25th September 2011, 07:55

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    Re: Twilight Switch component and circuit help

    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 diagramTwilamp.png

    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...



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    Re: Twilight Switch component and circuit help

    Hi rjrocks,

    Thank you again for the indepth explanation. 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.

    Greetings and respect.
    Ashish

    Quote Originally Posted by rjkrocks View Post
    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 diagramTwilamp.png

    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...



    •   Alt27th September 2011, 03:56

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  6. #6
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    Re: Twilight Switch component and circuit help

    Hi Ashish,

    I have two queries;
    1. Any specific reason for using NPN transistor?
    .
    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.

    2. I was wondering if I can use an alternate to transformer as I want to make the circuit look sleek and less bulky.
    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.
    http://ww1.microchip.com/downloads/e...tes/00954A.pdf

    Hope that this clears all your queries............. and is helpful.


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    Re: Twilight Switch component and circuit help

    Hi rjkrocks!

    You really rock! Thanks again.

    Keep sharing.

    Regards,
    Ashish

    Quote Originally Posted by rjkrocks View Post
    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.
    http://ww1.microchip.com/downloads/e...tes/00954A.pdf

    Hope that this clears all your queries............. and is helpful.



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    Re: Twilight Switch component and circuit help

    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



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    Re: Twilight Switch component and circuit help

    Yes my friend its a commercial product and I never said that I developed it. Who developed that, I don't knew and thanks for sharing that info. Funny to read that you made me a "manufacturer". My dear friend, to sell milk, you don't need to know how the cow produces the milk!

    Appreciate the efforts of rjkrock and hope that you take things in right spirit my friend. Thanks again for promoting me from "Mr. No-one" to "Mr. Manufacturer".:-P


    Quote Originally Posted by pranam77 View Post
    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



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    Re: Twilight Switch component and circuit help

    Quote Originally Posted by ashishpostbox View Post
    My dear friend, to sell milk, you don't need to know how the cow produces the milk!
    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?.



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    Re: Twilight Switch component and circuit help

    Hi Ashish,
    How is your development with twilight circuit....... Hopping that you will be posting your experiments in DIY of Edaboard as Pranam77 said
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