Ok so I have this thing connected to my pc, it's a serial

Sorry I forgot to mention, if there's no signal, A is positive and B is negative, but when I send a signal, A turns negative and B turns positive, so I think a capacitor will just blow off

>>1234479
>Sorry I forgot to mention,

you need to post some more that start with that.

>>1234487
Like what?

>>1234489

seriously?

>>1234492
Well, that's all that I know about this thing

For a start: is it like rs323 serial, or a direct drive?

>>1234496
I'm not totally sure, but it's a card used for printers. The thing is to keep the 12v constant on the input of the relay. I have the idea, like those that are used on a full bridge rectifier, that prevent the voltage to fall

you want a latching relay and a driver for it
Serial device -> transistor -> relay coil
it toggles when you give it a pulse

Why don't you just, I don't know, keep sending the signal without stopping for half a second each time?

>>1234479
>I need it to be always off.
Then pull the plug.

>>1234514
The pulse is sent by a BAT file, so it reads the line (which takes about 4 minutes) then repeats the cycle, but when it's done reading the line, it turns back on

>>1234561
The idea is to be able to turn it on and off from my computer

>>1234479
Use either a latch gate or a flip flop between the relay if you want to toggle the relay on or off with the same signal

>>1234705
Obviously you should run a service to keep the serial line on or off, or get a smarter controller that latches.

>>1234705
>The pulse is sent by a BAT file
Post the content of your BAT file.

OP, what kind of bomb are you making?

Post pics