I'm creating an alarm that needs reed switches to run. Should I buy reed switches that are normally closed, or normally open and create a circuit with an inverter. How hard is it to create a circuit with a logic inverter? Does anyone have any circuit diagrams?
2007-12-10 04:20:54 · 4 answers · asked by thebestkiano@btinternet.com 2 in Science & Mathematics ➔ Engineering
Sorry, I mean the open and closed the other way around!
2007-12-10 04:27:53 · update #1
You need to use the normally closed reed switches in series and configure the circuit with a relay that sounds your alarm when any of your reed switches opens.
This is the most secure arrangement because your alarm will go off if your wires are cut.
This is really simple to do.
2007-12-11 15:57:34 · answer #1 · answered by goblin 4 · 0⤊ 0⤋
Actually, the state of the reed (NO or NC) can be important.
Imagine that you are running ac through your reed contacts from an external source to drive your alarm and the reed contacts are normally open. When the reed switch is off, the contacts are open and the ac does not pass through the reed switch. So if your device is turned off, the alarm will be off as well.
Now imagine the same situation when you are using a normally closed reed switch. If the reed switch is off. the contacts are closed and the ac passes through the reed switch triggering your alarm. To prevent the alarm, you have to energize the reed switch, opening the contacts, and thus disconnecting the ac from the alarm. So if your device is off, the alarm will be on.
While this is an easy way to trigger an alarm if the device which is controlling it becomes non-operational, it may not be what you are wanting; however, you can still control the alarm when the device is operational (energize the reed to turn the alarm off, de-energize the reed to turn the alarm on).
2007-12-10 05:48:45 · answer #2 · answered by Anonymous · 0⤊ 0⤋
From a pure logic point-of-view, it doesn't matter if your switches are N.O. (normally open) or N.C. (normally open). The circuitry to 'read' the state of the switches is no more difficult to construct, either way.
Here are some simple burglar alarm circuits:
http://www.zen22142.zen.co.uk/Circuits/Alarm/5zalm.html
http://www.aaroncake.net/circuits/alarm1.asp
.
2007-12-10 04:33:39 · answer #3 · answered by tlbs101 7 · 0⤊ 0⤋
challenging issue. research from google and yahoo. that will help!
2015-03-24 17:31:48 · answer #4 · answered by gail 2 · 0⤊ 0⤋