RTC-clock stops when electric bell rings by relay operation.

[tapu]

Dear All,
I have designed alarm clock project with ds 1307.Here I want to ring 230v electric bell in particular alarm time set by keypad.then I designed relay circuit.here relay opens & close normally acording to alarm time.But when I connect electric bell then bell rings & stops but clock also stops.please reply.

 

[srizbf]

Dear All,
I have designed alarm clock project with ds 1307.Here I want to ring 230v electric bell in particular alarm time set by keypad.then I designed relay circuit.here relay opens & close normally acording to alarm time.But when I connect electric bell then bell rings & stops but clock also stops.please reply.

did you test it with a proper pcb or just in a breadboard?

 

[KlausST]

Hi,

are you sure the the RTC stops working?

It is possible, but i think it´s more likely that a microcontroller stops working. This is because a microcontroller usually has mor I/Os with traces and wires to receive the electromagnetic noise.
The RTC usually has relatively short traces (for RTC operation).

Usually the problem can be solved wit a good PCB layout, maybe additional filters.

Show us your circuit, so we can give better advice...

Klaus

 

[chuckey]

Make sure that you have a snubber across the bell contacts and the relay coil.
Frank

 

[schmitt trigger]

To be sure the RTC is really stopping, enable the square wave output. Then you may monitor the activity.

 

[tapu]

Dear All, I have made PCB of that circuit.Here is a circuit.
Here I connected sqw wave directly to led.it blinks but time does not change.

 

[KlausST]

Hi,

* all power supply decoupling capacitors are marked with 104, irecommend to use ceramic X7R 106
* a big bulk capacitor at 5V is missing. With the switched LED current I recommend 100uF tantalum
* no unconnected inputs. Here at the 574 and the eeprom. While this is true especially for Cmos devices, i recommend it for all devices.
* the two blinking leds should hahe independent current limiting resistors to ensure equal brightness. All the led current is flowing through the clock's vcc pins. I'd avoid this to ensure clean power supply. Here i'm talking about the chip's internal bonding wiring. I'm not sure if it is meant to drive 2x Led current.
* are all unused ucuntroller I/Os programmed to never float? Even temporary unused pins.
* GND should be a rock solid power plane. You may have a reasonable board size and additionally fast switched relatively high currend at the display.
* all the long data wires and control wires to the display and the I2C wires should be carefully routed not to pic up noise.
* consider a snubber circuit or varistor at the relay contacts.

This are mostely circuit considerations, but for sure the PCB layout will show additional things to improve.

Klaus

 

[tapu]

Dear Klaus,Thank you for reply,
where I have to connect unconnected inputs of eeprom & 74hc574?
I have to give vcc through tantalum capacitor?please reply.my power supply circuit that i have designed is here.

 

[KlausST]

Hi,

where I have to connect unconnected inputs of eeprom & 74hc574?

You may connect it to any valid logic level, (VCC, GND, pullup, pulldown, or any other signal.

I just realized: although the EEPROM connections are named with "A0, A1, A2" they are not connected internally. Datasheet says you may leave it floating. But i recommend to connect them to a valiid level - even if it is only to get a clean schematic.

(BTW: "clean schematic". Your schematic is veary hard to read, because there are so many unnecessary edges, loops and crossings. Pleas spnd some minutes to clean it up.)

I have to give vcc through tantalum capacitor?

Yes, between VCC and GND. An additional Tantalum with 10uF at 12V to GND helps additionally to stabilize 12V.

please reply.my power supply circuit that i have designed is here.

Power supply schematic seems to be OK. A proper PCB layout with GND plane is essential, too.

Klaus

 

[Deexith Hasan]

1)How u r making the relay to activate?...........lcd R\W pin is connected to ground and relay transistor base is connected to gnd and also with p1.4 of mcu....when u make p1.4 high u r directly shorting p1.4 with gnd.......check it..

2)use different power supplies for relay and mcu.......

3)ground or power the a1,a0,a2 of eeprom...

 

[tapu]

Dear All,
P1.4 is not shorted with gnd & lcd R/w in actual pcb.(by mistake in schematic).
I have tested by diffrent power supplies but problom is same.
what happen if a0,a1,a2 & pins of 74hc574 are left open?As I will connect according to your advise.

 

[tapu]

Dear klous,
Thank you for giving hints & sugesion.P2.1 was floating.I used it.then circuit runs without any problom. Here in circuit,I have given BCD data from P3 port. P3.4 to P3.7 is unconected.(becouse bcd requires only 4 pins)can it couse problom of floating?

 

[KlausST]

Hi,

can it couse problom of floating?

Yes. don´t leave it floating.

it´s just one or two lines of code to switch them to "pullup" (or "output) - then it is not floating anymore..

what happen if a0,a1,a2 & pins of 74hc574 are left open?

* oscillating
* crow bar current (increased VCC)
* receiving and/or sending out of electromagnetic fields
* latch up

Klaus

 

[tapu]

Dear klaus,Thank you for taking a time to concider my problom.Your considerations are valuable.only one thing I did not understand.

All the led current is flowing through the clock's vcc pins. I'd avoid this to ensure clean power supply. Here i'm talking about the chip's internal bonding wiring. I'm not sure if it is meant to drive 2x Led current.

I have to connect snubber parrellel to relay contacts?

 

[KlausST]

Hi,

You are driving two paralleled Leds with pin7 sout of rtc. This Led current needs to go through rtc vcc pin to inside chip, then to sout.
I see an rtc as a sensitive device - where elese is an absolute error of 10ppm relevant? Therefore i try to keep all influence away from rtc. Especially here the led current.

Snubber: as chuckey mentioned this is an important point. The snubber should avoid sparks across the contacts.

Klaus

 

[tapu]

Is this circuit is sufficient for protection in relay circuit?

 

[KlausST]

Hi,

this should work. But in the end it depends on your load.
The Snubber is drawn like a simple resistor, but there should be a capacitor in series with the resistor.

Test it and see what happens.


Hope this helps

Klaus

 

[tapu]

Dear Klaus,
One problom I noted sometimes,The bell starts ringing at alarm time but rings continously(as it should stop after one second) does not stop.then I OFF & ON the power then runs normally.please reply( here clock runs normally).

 

[KlausST]

Hi,

No, it is more likely the microcontroller stopped working before switching off alarm.

Klaus

 

[tapu]

Dear sir,microcontroller does not stop becouse clock runs normally during continous ringing of bell.Can it be a problom of transistor used in relay circuit?