Automatic Electric Bell

The relay coil is being energized automatically as soon as the AC bell is being connected to power source.I have connected a 1N4007 diode across the relay still the problem is same...Moreover the 16×2 LCD board and arduino uno board is malfunctioning as soon as the AC bell is being energized.please help

Please post a schematic of the project.

Hi,
Welcome to the forum.

Please read the first post in any forum entitled how to use this forum.
http://forum.arduino.cc/index.php/topic,148850.0.html then look down to item #7 about how to post your code.
It will be formatted in a scrolling window that makes it easier to read.

Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?

A schematic and your code are essential to helping you with your problem.

Thanks… Tom… :slight_smile:

The bell i am using is 240V AC bell…so is there any possibility to somehow stop the back emf…I have used a diode 1N4007 across the relay but still it’s of no use…can the relay be replaced by a TRIAC???

Thank you,
FutureTech

What is the actual 9V supply?
Can you post the data for the relay (coil current)?
The 4.7K resistor on the base of the transistor is way to high. 180 to 220 Ohms would better allow the transistor to saturate. Are you sure of the transistor pin out?
I see no diode across the relay coil. 1N4007 should be fine.
Why control the power to the RTC with output pins?

OP’s images. How to post images.

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I have connected the diode in reverse biased across the relay not shown in the schematic.If not through Arduino power pins how should I power up the RTC module???

In the diagram, the RTC is powered by A2 and A3. Not the power (+5 and ground) pins.

I have assigned them as power pins in my programme.A2 and A3 as power pins

How much current does that relay coil require? BC548 is only rated 100 mA and it will need a much smaller base resistor to get that, something like 470 - 680 Ohms.
Does the circuit work without power to the bell?

Yes the circuit works perfectly when the bell is not powered.But as soon as the bell is triggered the circuit is malfunctioning.Is the diode 1N4007 connected properly in the schematic???When the bell is not powered the circuit perfectly triggers the relay but as soon as the bell is connected it is malfunctioning again

FutureTech:
I have assigned them as power pins in my programme.A2 and A3 as power pins

This is not a good thing to do, gnd output is not EXACTLY gnd.
The output pins do not have bypass capacitors.
PLEASE connect then to gnd and 5V.
Can you please post a picture of your project?
So we can see your component layout.
Have you kept the 240Vac Bell wiring COMPLETELY away from the Arduino circuitry, and is the Bell wiring heavy enough?
Thanks.. Tom.. :slight_smile:

If you see in the schematic the relay as well as Arduino Uno is supplied by the same 9V supply and the relay is connected to the 240V AC bell.Do by any means is it possible that the 240V AC bell is sending a surge voltage back to Arduino????Also can I use an optocoupler or optoisolater to separate my Arduino logic circuit and the relay and bell circuit???

Hi,

  • Can you please post a picture of your project?
  • So we can see your component layout.
  • Have you kept the 240Vac Bell wiring COMPLETELY away from the Arduino circuitry, and is the Bell wiring heavy enough?

Thanks.. Tom... :slight_smile:

Hi,

You need to add a large film capacitor across the relay output. That will work.

groundFungus:
Why control the power to the RTC with output pins?

I bet the typical newbie problem: "I don't have any spare power/gnd pins!"

Just connect multiple wires to the same GND and 5V pins. Or use a solderless breadboard.

FutureTech:
The relay coil is being energized automatically as soon as the AC bell is being connected to power source.I have connected a 1N4007 diode across the relay still the problem is same...Moreover the 16×2 LCD board and arduino uno board is malfunctioning as soon as the AC bell is being energized.please help

You may be seeing a large amount of mains interference due to the sparking acrosss the bell contacts,
if its the sort with contacts.

Anyway tell exactly which bell you are using, all hardware should be listed in detail or we'll simply waste time
asking you for the details like this.

If its a bell with contacts and it doesn't have a snubber circuit, it ought to have a snubber.

If it doesn't have contacts its the relay contacts that are likely generating the EMI, and those ought
to have a snubber too.

When there's a lot of high energy interference like this all the low voltage stuff should be shielded with shielded cables, and get at a distance. Also any mains PSU you are using ideally ought to be of quality with decent filtering on the mains side.