I would like to make an alarm that goes off if the connection breaksSimplistically that is the same principle used in many electronics goods shops here... there is a loop that passes through tags on the goods and if the wire is broken the alarm goes off. A relay powered by the loop and an alarm on the normally closed contacts would do it?
I would like to make an alarm that goes off if the connection breaks,like if i wire something and someone grabs it and take it.Just for the alarm to go off.
If you give us a bit more detail on exactly how things are arranged and how you would like it to work, we can offer you much better suggestions.I agree.
Even simpler, long loop of wire, relay, a buzzer and a battery.That would work but it has two disadvantages to the SCR:
Use the loop to supply power to the relay coil, when the loop breaks the power to the coil is interrupted and the contacts close, feeding power to the buzzer.
Is there a clever way to implement a NC circuit to detect a connection break without using constant power on the relay?
Here are some examples of actual reed switches: (https://www.eevblog.com/forum/beginners/alarm-going-off-when-connection-breaks/?action=dlattach;attach=567058;image) | . . | This shows you how they work, using a permanent magnet: (https://www.eevblog.com/forum/beginners/alarm-going-off-when-connection-breaks/?action=dlattach;attach=567064;image) (In operation, it doesn't matter which way the magnet is oriented. The poles are shown here just tor illustration) |
What it looks like inside: (https://www.eevblog.com/forum/beginners/alarm-going-off-when-connection-breaks/?action=dlattach;attach=567076;image) | . . | The pre-packaged alarm system version: (https://www.eevblog.com/forum/beginners/alarm-going-off-when-connection-breaks/?action=dlattach;attach=567082;image) |
1 set | Alarm system reed switch and magnet set with NO (and NC) connections | . . | (https://www.eevblog.com/forum/beginners/alarm-going-off-when-connection-breaks/?action=dlattach;attach=567082;image) |
15m | Two conductor wire, suitable for outdoor use | . . | (https://www.eevblog.com/forum/beginners/alarm-going-off-when-connection-breaks/?action=dlattach;attach=567799;image) |
1 | 9V battery | . . | (https://www.eevblog.com/forum/beginners/alarm-going-off-when-connection-breaks/?action=dlattach;attach=567787;image) |
1 | 9V battery snap | . . | (https://www.eevblog.com/forum/beginners/alarm-going-off-when-connection-breaks/?action=dlattach;attach=567793;image) |
1 | Piezo buzzer (Preferably pulsed, IMO) | . . | (https://www.eevblog.com/forum/beginners/alarm-going-off-when-connection-breaks/?action=dlattach;attach=567805;image) |
I know this isnt exactly what y listed but is it the same?I have been looking at some of these listings - and you have to be very careful about what is "Normal" when they talk about NO or NC. Some refer to the situation where the magnet is close to the reed switch and some refer to the situation where the magnet is separated from it. Quite the opposite.
https://www.ebay.com/itm/5PC-NC-Recessed-Magnetic-Window-Door-Contact-Security-Safety-Alarm-Switch-Reed/252560310788?epid=2020512430&hash=item3acdc48204:g:SxAAAOSwnHZYmX8H:rk:3:pf:0 (https://www.ebay.com/itm/5PC-NC-Recessed-Magnetic-Window-Door-Contact-Security-Safety-Alarm-Switch-Reed/252560310788?epid=2020512430&hash=item3acdc48204:g:SxAAAOSwnHZYmX8H:rk:3:pf:0)
And would it be possible to set the "volume" on the piezo buzzer?Maybe by voltage?Here's the voltage/SPL chart for the one I picked (at random):