constant to momentary output info

Also should have asked how long the pulse input need to be to charge capacitor. My door lock unit only  give a 0.5s pulse

Sounds like you want a pulse stretcher, rather than a constant to momentary circuit. This setup won't work for what you're looking for. It needs an electronic circuit to do it; just using relays won't work. There are prebuilt units to output a timed pulse on a trigger input, or you could put together a DIY circuit, if you're willing to work with some solid state bits.

The reason why the above circuit won't do what you're looking for is because your input pulse is only 1/2 second. This setup needs an input that is switched on for a longer time than your desired pulse. If you really want to do it with relays, you would need to add a latching relay so that your 1/2 sec input will be converted to a continuous "on" signal. Then you could use this setup, and increase the size of the cap to get a longer ON time. Use the 12V signal output from the timed relay to keep the first relay latched, so it'll reset and ready itself for the next pulse. I generally wouldn't use this kind of setup for timed pulses (solid state driver will be much easier to get a long pulse than with huge capacitors), but if you prefer relays, it could be done that way.

Here are two options, take your pick- relays only: transistor driver: If you have space for a HUGE cap, go for door number 1. You'll need to adjust your cap size depending on what relay you're using, if it draws more power, a bigger cap is needed for the same delay, and vice versa. Door number two would be tiny and cost for the parts would be piddling. Door number three is to buy the commercially available pulse timer, just more money but simplest.

Yes, it's a transistor- The BS170 is a MOSFET, which you can basically consider a voltage controlled switch. They're available online at most electronics places, you can look at www.mouser.com and just enter the part number in the search. Should be under 10 cents each; buy a hundred for a buck and you'll have enough for a lifetime :) Just be careful when handling it as it will be more sensitive to static electricity until you get it all connected up in the circuit.

According to Mouser 100 of them will cost a whopping $12.  A buck will only get you a handful at $0.16 a piece!Kevin Pierson

Oops, don't know what I was thinking- I was at qty of 10, not 100. Yeah, it'll cost more than a buck for that many. I got 100 for 10 cents a piece, looks like they went up to 12 cents now. I stocked up, so I don't look at the prices any more. I'm set for life anyway.