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alagiri
Joined: 30 Jun 2008
Posts: 1
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 30 Jun 2008 18:30 555 timer does not return to Ground state |
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I needed a DC motor to be running for particular duration. I wired a 555timer. The 555 was made to power a relay so that the relay would make/break the power to motor.
I observed that the moment the timer is triggered, the 555 goes to ON state but doesn't return back to low state even after the RC duration. Can somebody suggest why this happens?
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matbob
Joined: 15 May 2008
Posts: 5
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| 30 Jun 2008 19:49 Re: 555 timer does not return to Ground state |
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| Could you please post the circuit?
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viperpaki007
Joined: 02 Jul 2008
Posts: 37
Helped: 1
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| 03 Jul 2008 11:13 Re: 555 timer does not return to Ground state |
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| It can probably be due to the inductance of the relay coil...inductor will cause the current to keep on flowing even after the 555 has given zero logic at it output...so i think the best way is to use a transistor instead
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davidgrm
Joined: 08 Apr 2006
Posts: 159
Helped: 10
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| 03 Jul 2008 13:47 Re: 555 timer does not return to Ground state |
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| Use a transistor. Also put a diode in reverse across your relays coil. Put a 100u capacitor across the 555 supply line
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randell_xtian
Joined: 25 Mar 2008
Posts: 147
Helped: 7
Location: Philippines
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| 04 Jul 2008 4:29 Re: 555 timer does not return to Ground state |
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you can try the suggestion by davidgrm. it will work.
best regards,
randell_xtian 
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viperpaki007
Joined: 02 Jul 2008
Posts: 37
Helped: 1
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| 08 Jul 2008 4:54 555 timer does not return to Ground state |
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Davidgrm suggesstion will work but you can also use a power transitor (depending on motor rating) in darlington configuration as a fast swicth.
I think TIP121 will be good if you dont have much biggger motor.
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nagender
Joined: 11 Jul 2008
Posts: 3
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| 11 Jul 2008 14:58 Re: 555 timer does not return to Ground state |
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| i think u have connected the discharge pin to relay,in relay inductor will be there, it stores some energy so even though the 555timer is in off position you are not able to observe it plz try it by connecting the discharge pin any other i mean resistor and capacitor
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