Convert constant +12V to pulse

[CustomTrading]

• Open or close my front gate via a text message.
  
  Unless there is a better way, the main project (and my biggest issue) is to convert a constant +12V to a single pulse that activates a remote control.
  
  I have the Unimax HSPA+ Ethernet Modem Router with I/O Board
  
  http://shop.maxon.com.au/unimax-hspa-ethernet-router/
  http://www.maxon.com.au/images/manuals&drivers/Unimax+_HSPA_IO_Board_V1.pdf
  
  The modem/router is already to turn on (+12V) one of the outputs when I send a text (Gate On). Sending another txt (Gate off) will turn off the output.
  
  I need to use the +12V output to activate the remote that opens/closes the front gate. I assume this will involve converting the +12V output to a single pulse.
  
  The remote I use to open & close the gate is a Magic Button MBTX4
  http://www.mkey.com.au/remote,172,Magic_Button,MBTX4,MBTX4
  
  I imagine the process working something like this –
  
  To open the front gate from the closed position
  Send txt (Gate On) – Applies +12V to the output of the I/O Board.
  Convert +12V to a pulse to activate button 1 or 2 (both buttons are programmed to open or close the gate) on the remote to open or close the front gate.
  Send txt (Gate Off) – Turns off +12V output on the I/O Board.
  
  The same process will need to be followed to close the front gate again.
  
  How do I do this? Who can build it? What will it cost?

 

[CDRIVE]

There are times when a simple (series wired) capacitor will suffice to convert a steady state voltage to a pulse. The pulse will be generated on the leading edge of the control voltage when it switches from 0V to (in your case) +12V.

Other options would be a Monostable Flip-Flop that can be constructed from discrete components or IC's. The 555 Timer is arguably the most ubiquitous but not necessarily the best or only solution available to you.

Chris