Hi all,

I have built a circuit that consists of a NE555 and a relay powered by a 12v power supply and with an output of 12V. The operation of it is that is triggered by pin 4 of a RS232 and cuts of power to the output for a time dependent on an RC circuit.
What I want to do is to isolate the signal comming from the RS232 to the rest of the circuit after the relay is triggered. Does anyone have any ideas??

thank you for you time everyone!!!!

aris

 

Hello,

I moved you thread to the general chat forum.

Can you post a schematic of what you have upto now?
You can place a line where the isolation should take place.

You could think of an optocoupler as an isolation device.

Bertus

 

You only want to isolate the RS232 after the relay has been triggered?

Can you further define your task, and as bertus already asked, upload a schematic?

 

thank both of you guys!
what I want to do is to isolate the input comming from the RS232 after it has triggered the relay. This is the area in the red box in the attached schematic.
if you have any idea please share it with me

thanks all of you!!

 

You can use optoisolators that will only pass a signal when there is a signal to pass, then it is no longer in the circuit.

You can also use a DPDT relay and connect the RS232 to the NC pins. When the relay is energized, there will be no connection to the RS232. When the relay closes, it will be reconnected to the RS232.

 

just a question retched!
the 555 timer is activated by a low which gets from the rs232 when a computer is rebooted then the power is turned off (the box is powered by a 12V power supply) which means that once the existing relay is triggered it cuts the power to the box which leaves the rs232 in a low. what I want is when the existing relay is triggered to isolate at that point the low which comes from the rs232. would a DPDT relay would do that?

thanks again.

 

Sure, once it is triggered, wire the relay to pull the trigger to ground. That will keep a constant LOW on the 555.

Before energizing, the pin is getting 5v through the relay from the 232. once the relay is energized, you have the NO contact on the other site to ground.

So not energized, trigger is connected to rs232 through the relay
After energize, trigger is connected to ground through relay.

 

can you suggest any device for a DPDT so I can buy one to have a go?
I live in UK.
Thank you very much!!!

 

http://www.jameco.com/webapp/wcs/st...toreId=10001&catalogId=10001&productId=139977

here is one with a 5v coil. You want to find one that has the coil voltage that you want to use.

here is a 12v coil:
http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_99311_-1

 

thanks a lot retched for your help!!!
I will get those and I will give you some feedback possibly on monday
Thanks once more!!!

 

Ok. Let me know how you get on.

 

Just a final question retched!!
If I want to have a delay before passing the signal to the DPDT relay would a resistor and Capacitor do the job?