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    This 6V battery operated doorbell light circuit can be connected in parallel with any existing AC230V doorbell. When anyone push the doorbell switch, the bell sounds as usual and ac mains supply available across the doorbell is routed to the input of this circuit through an opto-coupler(IC1).

    Conduction of IC1 triggers a monostable, wired around the good old 555 timer (IC2). As a result the high-bright white LED (D2) at the output of IC2 is switched on for a short time. This circuit is highly useful at night/midnight as it gives sufficient indoor light to help you locate switches for room lamp/porch light, etc. On/Off duration of the LED light can be increased/decreased by increasing/decreasing the value of C2.

    The electronic doorbell light circuit is fully safe because it is perfectly isolated from the fatal ac mains supply by IC1. However, keep to avoid accidental contacts with the front end of the circuit, which is directly connected to the ac supply. Use of a good and convenient ABS enclosure is recommended for this doorbell light unit.

    Electronic Doorbell Light Circuit Schematic

    electronic doorbell light circuit schematic

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    17 Responses to "Electronic Doorbell Light Circuit"

    1. The LED in the opto isolator would fail due to high reverse voltage of the mains, a diode should be added anti parallel with it.

    2. During testing,reverse voltage measured across the input of IC1 is well below the value specified by 4N35 mfr.Although I’ve not tested my prototype with the anti-parallel diode,I welcome your comment.Thanks!Further,an ac opto-coupler like NEC2502 can be tried in place of IC1,which obviatesthe requirement of the additional diode.

    3. In my reply to Mr.Sivanand, Part number of the recommended opto-coupler is wrongly indicated as NEC2502.The correct part number is PS2506-1.

    4. Help me~.

      On the circuits, The 555 part is not a compatible general IC 555. I am sure.

      I have use IC ST555 (or TLC555CP) for the small power consumption. This has critical issue for the applying circuit.
      The LED light is on whenever the battery is inserted the holder.

      It was critical issue. If you make this, you should know that the LED lamp is lighting whenever the other room switch is on with AC spark.

      If I had use LM555CN, there is no problem. But this(LM555CN) has large consumption at standby mode.

      Which parts is changing on the circuits if I use IC ST555 (or TLC555CP)?

      Please do reply if you fix this.

      I am serious.

    5. Thanks for your interest in my circuit.I’ve tested the circuit with both NE555&LM555.Regarding the false triggering,I think,grounding pin 5 of IC1 through a 100nF(0.1uF) capacitor may rectify the problem.

      • I have tried this (inserting 100nF capacitor) after your reply. It has no effect. (The model ST555 is wrong part number. The corrected number is TS555. Thanks)

    6. Try to keep all wiring in connection with pin 2 of 555 as short as possible.Next,clean your PCB to remove solder flux traces.Finally,replace R2 with a trimpot and retune it to get the best result ie no false triggering.Still,I’ve faced no problems with my prototype,I will retest it and give you a feedback ASAP.Thanks!

    7. It has no effect too.
      I have replace R2 with trimpot 200K ohm. The LED turns off with the large current flowing when the trimpot has go 0R8.
      I have been testing on the breadboard, too.
      It was failed, too.
      Should I change the IC to the original LM555 only?

    8. [Resolved] This is the making note. It takes long time. I had not solved its based problem but I have resolve high voltage (230V) sparking trigger issue. If you use TLC555CP IC or TS555 IC, you should use the commercial ‘AC noise filter’. It would solve the problem (The LED lamp is on when the other room switch bring the spark.).

    9. i want to use 555 as timer light control.

    10. Tell me equivlent of 180nf capacitor

    11. tell me the difference between capacitor condancer.

    12. No difference –condenser is simply an older term that predates solid state electronics –use of the term condenser was much more common when I was a child some 60years ago –today capacitor is the preferred term.

      • Jim Keith says: on October 30, 2012 at 8:16 pm

        An exception is the term “condenser microphone,” but anyone who says capacitor microphone is fully understood.

    13. Colin Mitchell says: on August 1, 2015 at 2:26 am

      No opto-coupler will withstand 250v as a reverse voltage across the LED.
      The data-sheet clearly states 6v.

      What is the purpose of D1??
      No current limiting for the LED.
      T.K.Hareendran does not know what he is doing or what he is talking about.
      Do not build this circuit.

      • Good day to you M. Mitchell.

        The 4N35 maximum reverse voltage is 6V as per the datasheet, so obviously that won’t work too well with 240Vrms !!!

        For the PS2506-1, I didn’t find any reverse voltage specification, however seeing 2 diodes and information about 2 CTRs values, rises a lot questioning.

        I guess this circuit, along many others, will deserve a place in your “Spot The Mistake” hall of fame series.

        As far as the missing current limiting resistor, the circuit creator simply got lucky. Considering the 555 voltage drop at the pin 3, plus the 0.7v of the 1N4148, he got close to the white led operating forward voltage. If someone increases Vcc, then the led will obviously be in trouble and the 555 as well for that matter.

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