Having a problem on my relay, Pls HELP !

[jeyes56]

Hi,
i have a problem regarding on my relay (or some parts of the circuit).

in my circuit, when the switch is open, the relay must be open (inactive);
when the switch is closed (and open after a few seconds), the relay should be closed (activate) for around 10seconds.

we'll, my circuit is working fine, from the start where the power source is turned on, until before the power is turned off...

MY PROBLEM is:
when i turn off the power, the relay is activating (closing), which is not supposed to happen because it ruins my project..

does the load from the relay affects the problem?
my instructor before always saying that we must always use tantalum in pin 5 of LM555, (haven't tried yet): does this affect my circuit?

**broken link removed**

 

[jeyes56]

i forgot to mention, the relay requires 6volts to activate...

 

[jeyes56]

by the way, the use of my relay is to connect two wires like an switch or button.. if you have alternative method of doing this, Please suggest.

 

[jeyes56]

pls help me, any suggestion?

 

[ronv]

Just to make sure..... It is when you turn off the power switch that the relay energizes?? Do you have decoupling capacitors on the power pin of the 555?
Ceramic is fine for pin 5.

 

[jeyes56]

the circuit is working fine, but, additionally, when i off the power switch, the relay is energized; i don't want to energize the relay when i off the power switch. sorry, I'm not familiar with capacitors, what is a decoulping capacitors? all the components i used are in the image, (except for the load of the relay). also i have a capacitor between Vcc and Gnd (not in image)

 

[jeyes56]

please help me...

 

[ronv]

Hmmm. I can only guess. The circuit should work.
For the relay to energize you must still have at least 6 volts on Vcc after power is turned off. This tells me the capacitor from Vcc to ground (Decoupling cap.) must be on the IC side of the switch. The capacitor will take a long time to discharge if it is large. This may make the circuit susceptible to noise on the trigger line. Make sure to have the 10K from trigger pin to Vcc. If so move the capacitor on Vcc to ground to the battery side of the switch and see what happens.

 

[jeyes56]

yes, but isn't it that the lm555 timer is giving a 6v+ output that will trigger the relay?, i guess that the problem is in the timer, because when i switch off the power, the timer is giving a 6v+ to the relay..

 

[jeyes56]

is there another way so that i can replace my relay? i'm using the output of relay to short the button of a cellphone (number 9 button). i used relay so that no additional current will be sent to the cellphone.

 

[aljamri]

Hi;
Go for the below linked site and see the sidebar 555, you will get valuble information, elese, you are welcome here to ask for clarification

TE Index for website

 

[ronv]

I think your circuit has a "bug". Here is the deal:
For the 555 to trigger it needs a low on the trigger pin. Since you are not pushing that switch when you turn the power off it is either picking up noise on the trigger pin or the 10k resistor is not pulling it up to +9 volts. Keep the wires short to the trigger pin and make sure the 10k is going to +9.
Even if there is noise on the trigger line the relay needs +6 volts to pick. Since you just turned off the voltage to the circuit there should be no voltage to pick the relay. But you have a big capacitor from Vcc to ground (probably at the 555) that can supply the voltage to pick the relay for a short period of time. If you move this capacitor to the other side of the switch there would be no voltage to pick the relay. No voltage no problem. Make sure your circuit is neat and correctly wired. Try these things and then we can use a FET to replace the relay, but lets get the circuit working right first.

 

[jeyes56]

ok, i will try this later when i arrive at home,, i'm not online for how many days,,