I have DPDT relay which I would like to energize using pulse signal (duration of that pulse should be adjustable) and switch. When switch is on, coil of relay is shortly energized by pulse signal and then deenergized when pulse signal ends, although switch is maybe still closed. When I open switch, nothing happens but when I close it, process repeats. Any idea how to implement this circuit? Relay model is Omron DPDT 10A 12V DC. Thanks in advance

 

The common approach is to use a 555 IC timer configured as a one-shot (astable) to provide a pulse to the relay when it is triggered by the switch.
Does that sound like something you could build?
What is the relay coil current?

 

Hello, thanks for reply. I have basic knowledge of 555 but I'm not sure I can use it in this situation.
I looked for solution using 555 timer but it will not work in my case. Here is example of monostable 555 timer: http://www.electronics-tutorials.ws/waveforms/555_timer.html

If I put switch between pin 2 and ground and close it, output will be high but it will not go low itself If I keep switch closed. I need output to go low even if I keep swith closed for long time. They say also:

"The Monostable 555 Timer circuit triggers on a negative-going pulse applied to pin 2 and this trigger pulse must be much shorter than the output pulse width allowing time for the timing capacitor to charge and then discharge fully."

 

http://www.doctronics.co.uk/555.htm#triggering
and put your switch across where it says Vin.

 

A CMOS 4528 or 4538 is a much better solution. These can be configured for edge triggering. Manufacturers are ON Semi (MC14528, MC14538) or Texas (CD4528, CD4538). You'll need buffering of the output to drive the relay (a transistor and a couple of resistors). And you might need debouncing of the input, which the second half of the 4528/38 can take care of.
A 555 is not the cure for all ills. In fact I hate it

Cheers,

Benta.

 

16 pins where 8 would do the job?

 

The bipolar 555 has the advantage over the CMOS timers of providing a much larger output current.

I'll ask the question again: How much current does the relay coil require?

 

The bipolar 555 has the advantage over the CMOS timers of providing a much larger output current.

I'll ask the question again: How much current does the relay coil require?

I think it's 75mA.
This is relay I have http://www.ebay.com/itm/Relay-Omron...969959?hash=item566775f067:g:hmoAAOSwKsRWFmAP

 

If I put switch between pin 2 and ground and close it, output will be high but it will not go low itself If I keep switch closed. I need output to go low even if I keep swith closed for long time.

AC couple the trigger. If you post a schematic, you'll get a more detailed answer.

 

Hi

This should do what you want.
This 555 Monostable "one shot" circuit produces an output pulse when the input switch closes, triggering the timer.
If the switch remains closed, the output pulse will return low only after the duration of the time setting.
If the switch closes again, time cycle is started again.
I didn't know the pulse duration you wanted, so I picked an arbitrary value.
See attached.