Help me !! Relay's Problem ( SMS Based Device Control )

[psrkiran]

I am attaching the circuit diagram of my project
Serial Communication (MAX232) and LCD are working perfectly
i have so many doubts regarding my circuit
1) is 12v 1 amp transformer is sufficient to drive 3 relays using uln 2003
2) is it mandatory to ground the un used pins of uln 2003
3) in terms of performance, using uln 2003 is recommended or using individual transistors is recommended ( not in terms of cost or easy design )

Problem : some times when i clear P1.1 (relay 2) relay1 is also getting cleared and form there eventhough i set p1.0 (relay 1) it is not taking place why all this happening
please help me

 

[lockman_akim]

put protection diode to your coil..

---------- Post added at 11:57 ---------- Previous post was at 11:55 ----------

Problem[/U] : some times when i clear P1.1 (relay 2) relay1 is also getting cleared and form there eventhough i set p1.0 (relay 1) it is not taking place why all this happening
please help me

it like noise that cause from back EMF of relay..
put protection diode at your relay coil..

 

[wp100]

Hi,

lockman_akim
put protection diode to your coil..

The ULN2003 has the protection diode built into the chip so there is no need to add any additional ones.

Its an industry standard part to save using all those separate transistors, diodes and resistors.

That chip is able to drive 8 relays so cannot see any problems with just 3 from your 1A PSU. - though you do not detail what relays you are using ie their resistance /current

Unused gates are best tied to ground or +, leaving them open can cause its output to oscillate.

Your port problem could be software or interference from the load the relays are switching, you may need a contact suppressor on the relays contacts if you are switching mains or heavy loads.

The rest of your circiut, you have C4 or 1MF !! - 1000uf to 4700uf is more than enough.
Across the pos and neg connections to each chip used fit a 100nf cap as close to those pins as possible.
The same with the crystal and its caps - as close to the chips pins as possible.

 

[psrkiran]

Thank u so much for ur reply


That chip is able to drive 8 relays so cannot see any problems with just 3 from your 1A PSU. - though you do not detail what relays you are using ie their resistance /current

These are the Relay specifications which i am using

 

[alexan_e]

It is a 12v/400 ohm relay, needs only 30mA @12v
JQC-3FC pdf, JQC-3FC description, JQC-3FC datasheets, JQC-3FC view ::: ALLDATASHEET :::

Alex

 

[psrkiran]

Your port problem could be software

I tested my program on development board and it worked without any problems

---------- Post added at 18:47 ---------- Previous post was at 18:45 ----------

you may need a contact suppressor on the relays contacts if you are switching mains or heavy loads.

I am just switching 10 Watt - 15 Watt Bulbs

 

[alexan_e]

Can you please post the complete part number of your mcu,I can't find a datasheet for 8052, only some brochures.
Also double check that pin 9 of ULN2003 is connected to the positive voltage.

Alex

 

[wp100]

Hi,

You say your bulbs are 15w, I assume thats AC mains ?

Try a mains suppressor across the contacts of the relay - I had a similar problem yet the load was only 3 watts.


I only use the Pic micros but notice your 8052 has a Reset pin.
Pic chips need that pulling high with a resistor - but do not know if your 8052 needs something similar ?

Also any long and loose unshielded wires can pick up interference from switching relays and their loads and cause the micro to do strange things.


Edit - when fitting suppressors ensure you use only parts designed for your AC mains voltage.

 

[psrkiran]

You say your bulbs are 15w, I assume thats AC mains ?

Thanks for your reply,


Yes they are AC Lamps !

---------- Post added at 21:18 ---------- Previous post was at 20:57 ----------

Pic chips need that pulling high with a resistor - but do not know if your 8052 needs something similar ?

Yes it is actually AT89S52 Which need pullup Register across Port0 i used it in my PCB ( but not shown in circuit diagram )

---------- Post added at 21:26 ---------- Previous post was at 21:18 ----------

Try a mains suppressor across the contacts of the relay - I had a similar problem yet the load was only 3 watts.


Edit - when fitting suppressors ensure you use only parts designed for your AC mains voltage.

I understood what u said
but i dont know how these contact supressors look like, their name and where to connect them in PCB
please give the information about them

Also can i use another relays which have in build contact supressors or which eliminate this effect when contact occurs ?
if so give info about those relays

---------- Post added at 21:29 ---------- Previous post was at 21:26 ----------

Can you please post the complete part number of your mcu,I can't find a datasheet for 8052, only some brochures.
Also double check that pin 9 of ULN2003 is connected to the positive voltage.

Alex

Thanks for your reply

That is AT89S52
datasheet : AT89S52

 

[alexan_e]

So your outputs are open collector/drain , are you sure that everything is ok on the output part,
you can only sink about 3mA from the pull up resistor and the output will be about 0.45v,
what value resistor have you used to pull up your outputs?
This pull up resistors are an important part in an open drain circuit, you shouldn't remove them from the schematic shown.

Alex

 

[psrkiran]

So your outputs are open collector/drain , are you sure that everything is ok on the output part,
you can only sink about 3mA from the pull up resistor and the output will be about 0.45v,
what value resistor have you used to pull up your outputs?
This pull up resistors are an important part in an open drain circuit, you shouldn't remove them from the schematic shown.

Alex

Each pull up register value is 10K 8 register each across each pin of port 0

 

[alexan_e]

So this is ok too, you are using the typical 10k pullup and the current will be about 0.5mA, no problem there

I understood what u said
but i dont know how these contact supressors look like, their name and where to connect them in PCB
please give the information about them

WP100 has provided a link in his post

, you can try it to see if it helpls.

Alex

 

[psrkiran]

So this is ok too, you are using the typical 10k pullup and the current will be about 0.5mA, no problem there



WP100 has provided a link in his post

, you can try it to see if it helpls.

Alex

Please recommend a snubber network for the specifications which i used

 

[wp100]

Hi,

Your lamps are resistive so you need to connect a suppressor as shown in that diagram across the contact points, supply to load.

Do not miss the point that the suppessor does leak a little so the circuit is not totally dead when the relay is off.

Just visit your local shop or search any online electronic supplier in your area for ' contact suppressor ' 100r/ 0.1uf 230vac class X or Y - they are a very common part.

 

[psrkiran]

I forgot to say one thing in my PCB that i used a insulated wire of about 8cm long from 7812 (present at one end of PCB) output (VREG) to the another end where 3 Relays, 100uf and 0.1uf capacitor are present

Is this causing any problem ??

---------- Post added at 06:45 ---------- Previous post was at 06:41 ----------

also can you recommend me a relays which have in bulid contact supressors

 

[jayachar88]

Pics of 'Contact Suppressor' are here AMPOHM WOUND PRODUCTS|FE-SP-CR23-220/100|CONTACT SUPPRESSOR, 0.22UF, 100R | element14 Malaysia

 

[wp100]

I forgot to say one thing in my PCB that i used a insulated wire of about 8cm long from 7812 (present at one end of PCB) output (VREG) to the another end where 3 Relays, 100uf and 0.1uf capacitor are present

Is this causing any problem ??

---------- Post added at 06:45 ---------- Previous post was at 06:41 ----------

also can you recommend me a relays which have in bulid contact supressors

Hi,

No that wire should be ok.

Never seen relays with suppressors built in as there are so many different configurations needed. - just fit a standard contact suppressor as mentioned.

 

[ecnbom]

Help me !! Relay's Problem ( SMS Based Device Control )
I am attaching the circuit diagram of my project
Serial Communication (MAX232) and LCD are working perfectly
i have so many doubts regarding my circuit
1) is 12v 1 amp transformer is sufficient to drive 3 relays using uln 2003
It is OK that ULN2003 drives 3 12V relays, the total current of 3 pcs 12v relays is less than 150mA, while ULN the capacitance is greater than it.

2) is it mandatory to ground the un used pins of uln 2003
No need.

3) in terms of performance, using uln 2003 is recommended or using individual transistors is recommended ( not in terms of cost or easy design )
It is better to choose ULN2003, since a darlinton is implemented, that means no need to add a current amplifer in some case, the IO capacitance is not enough.


Problem : some times when i clear P1.1 (relay 2) relay1 is also getting cleared and form there eventhough i set p1.0 (relay 1) it is not taking place why all this happening
please check IO status, the 7 channels are indenpent.
please help me

 

[farfary52]

hi
your project is very nice .can you send for me this project source code please
i want control relays with gsm modem
thank you