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[SOLVED] problom in automatic control system.

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tapu

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Dear all,
I am controoling electric bell at particular clock times.which is set by keypad.but when I connect two bells(230v ac )as requirement then after ringing rtc 1307 stops. Here I am using 89c52 ,5v DC/5amp relay and transistor bc547 for switching relay.please reply.

Thanks,
 

If it works with one bell but not with two, the problem is that inductive kick-back from the contacts when opening is somehow getting back into the circuit. Check wiring and layout, keep the power wiring well separated from logic supply and signals.

Put a snubber across the contacts. I suppose you have the free-wheeling diode across the relay coil. Add bypass caps across the IC's.
 
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    tapu

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Hi,

EMI /EMV.

Use a proper layout. Solid ground plane.
Stable VCC, reliable GND.
Put filters in signal lines.
Avoid ringing.
Use shielding.

Most probaly it is a PCB layout problem.

Klaus
 
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    tapu

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Thank you for replies.the PCB has solid ground plane and I use adaptor 5v DC/2 ampere as power supply.here how to add filters?I have to use varistor and shielded cable?
 

Thank you for helpfull replies.in PCB bell connector & its internal socket are opposit to each other.therefore cable passes through above the controller and rtc circuit.but now how to shield circuit and connect filter.
 

Try this. Lay a piece of bare wire along the cable where it goes above the circuit. Wrap the cable and wire with aluminium foil along the same length. Ground the other end of the wire. Be careful not to get too close to any exposed power terminals. If needed wrap some insulating tape over the foil.

The wire grounds the foil which acts as a shield. I've never done this, so I can't guarantee that it will work, but you have only some time and a bit of foil to lose.

Whether it worked or not, please report back.
 
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    tapu

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I think the best way to go is to keep the RF transients around the bell circuits, so I would earth the metal work of the bells and connect a 1NF cap from each terminal to the case of each bell, and perhaps a ferrite bead on each lead at the bell end.
Frank
 
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    tapu

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I expect a conducted EMI problem in a first order. If so, shielding won't help much. A possible exception is a 230V wire running near the DS1307 crystal which could cause problems though.

Filters and/or overvoltage suppressors for all external signals connecting to the controller board would be the primary means to get rid of the problems. Also sufficient bypass capacitors for the internal 5V supply node.

Where did you place the 230V relay?
Is the keyboard on the controller board or externally connected?
Can you show a photo of the controller board and external cabling?
 
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    tapu

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Add more capacitors on Vcc and Vbat of rtc 1307.
Need more details about bells (what kind of?), power supply, distances between.
 

Dear all,
Sorry for replying late. I completely separated relay switching circuit from control circuit. (In same body)then timer runs without any noise and error.but I will shield circuit for safety as advised.
Thanks,
 

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