exact time delay ckt

Discussion in 'General Electronics Chat' started by bahubali67, Feb 21, 2013.

  1. bahubali67

    Thread Starter New Member

    Mar 15, 2012
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    hi all,,I have made ckt using 8951 micro controller which is having 1.5min on delay. and 30min off delay. I got the output and planned to apply for my borewell pump. initially worked fine but after some on and off delay (say 3rd or 4th on delay ) it is not working as I had mentioned in program (1.5min on and 30min off ). what could be the problem????

    block diagram:

    micricontroller ----->uln 2003----->relay
     
    Last edited: Feb 21, 2013
  2. #12

    Expert

    Nov 30, 2010
    16,308
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    The micricontroller might not be sending a signal to the transistor array. Part of the transistor array might be bad. The relay might be bad.
     
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  3. bahubali67

    Thread Starter New Member

    Mar 15, 2012
    28
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    so any solutions... controller sending signal correctly... am using uln 2003 made in china... I hope tat might be problem.. so how to solve this. I need exact time delay (24*7).
     
  4. #12

    Expert

    Nov 30, 2010
    16,308
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    Why would you say (again) that you "need exact time delay" if the controller is "sending signal correctly"? "Sending signal correctly" means it is sending the exact time delay you want. Which is it? Sending signal correctly or you still need to correct the time delay?

    As for the uln 2003 or the relay, I can not measure the voltages from here to see which one is not working. Can you measure voltages? How do you know the controller is sending signal correctly if you have bad transistors or relays?
     
  5. Brownout

    Well-Known Member

    Jan 10, 2012
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    One helpful thing to do is insert an LED on the output of your uC, properly current limited with a resistor. If the LED lights up at the prescribed time, then the problem is downstream, transistor, relay, etc.
     
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  6. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    What did you connect pin 9 (COM) to?

    Always post a schematic, otherwise we are just guessing here.
     
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  7. bahubali67

    Thread Starter New Member

    Mar 15, 2012
    28
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    see I have mentioned above initially it works properly but after 2,3 cycles (3 on delay and 3 off delay ) it doesn't work(some time it won't turn on after 30min or if it's turned on then the time delay will be more than 1.5min). that's wat I want exact time delay but the circuit fails after 2,3 cycles. if u reset the ckt again ckt works fine till 2,3cycles after tat fails .

    I can measure signal using multimeter when controller is not connected to uln 2003(if u measure when controller is connected to uln 2003 it won't show correct reading )

    relays r working fine... instead of uln 2003
    any other ckt tat works better???
     
  8. bahubali67

    Thread Starter New Member

    Mar 15, 2012
    28
    1
    I have connected led to uln output which shows correctly(when ckt is not connected to pumpset ) but when I connect ckt with pumpset using relay it fails after 2,3 on and off cycles.
     
  9. bahubali67

    Thread Starter New Member

    Mar 15, 2012
    28
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    vcc. that is 12v
     
  10. Brownout

    Well-Known Member

    Jan 10, 2012
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    After the system fails, if you disconnect the realy, will the uC and LED work again? By that I mean, is permanent damage done to your components when the system fails?
     
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  11. bahubali67

    Thread Starter New Member

    Mar 15, 2012
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    ya after disconnecting relay uc and led works fine. after resetting ckt everything works fine..
     
  12. bahubali67

    Thread Starter New Member

    Mar 15, 2012
    28
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    ya works.. after resetting everything works fine..
     
  13. MrChips

    Moderator

    Oct 2, 2009
    12,446
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    Did you put diode protection across the relay?
    Did you put 0.1μF capacitor and 10μF electrolytic capacitor across the mcu power pins?
     
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  14. Brownout

    Well-Known Member

    Jan 10, 2012
    2,375
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    Yeah, it does sound like a power supply glitch. Try the clamping diode across the relay coil. Use a fast diode like the 1n4148 or a shottkey diode. Attach the power supply bypass caps at the power supply pins. If all that doesn't work, you could try to isolate the relay on a seperate power supply, and use an opto-isolator between the controller and realy. Relays can wreck havoc on a contoller through the power supply wires.
     
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  15. bahubali67

    Thread Starter New Member

    Mar 15, 2012
    28
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    block. diagram
     
  16. bahubali67

    Thread Starter New Member

    Mar 15, 2012
    28
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    yea diode is there across relay.
    I haven't used electrolytic capacitor... wy should I use???
     
  17. bahubali67

    Thread Starter New Member

    Mar 15, 2012
    28
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    we use one diode with parallel connection to relay to protect microcontroller from BACK EMF which is generated when relay come is original position from its operational condition.

    so does it matters of using fast diode or normal diode? OK will try it.

    which capacitor should I use for bypassing??
     
  18. Brownout

    Well-Known Member

    Jan 10, 2012
    2,375
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    See post #13 for capacitor values. It's important to keep the voltage connected to the microcontroller noise free. Otherwise, your controller does weird things like the things you've described. Bypass caps help to filter noise from the power rails. They are always required.
     
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  19. bahubali67

    Thread Starter New Member

    Mar 15, 2012
    28
    1

    I have placed 0.1uf(ceramic capacitor ) at output side. where should I place 10uf capacitor. (now I have placed 1uf capacitor at input side )
     
  20. Brownout

    Well-Known Member

    Jan 10, 2012
    2,375
    998
    Place both at the power pins. I don't know what you mean by the "output" side. Both go on the power pins. Try googling power supply byapss or power supply decoupling for more information.

    Oh, and place the caps as close as possible to the power pins. Especially the .1uF cap.
     
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