Hi,

I'm new to this forum and taking again electronics after some years of other stuff.

So I ask for you help with a "simple" problem, the this is I have a magnetic contact (the ones tha someone use in a door/window alarm tha is normally open (I guess.....is closed when the magnets are together and open when they are separeted).
So what I want to do is energize a circuit when the magnets are separted (sensor normally open) and cut the energy when they are together, something similar to the attached image.

I've tried attaching another magnet with the same "magnetic field" in an oposite direction but it's to complicated and as I wan to have in one sall circuit that it's nor a feasible option, also someone recommend me an "inversor reed switch" (a deed with 3 terminals) but I looked for one and I was unable to find it locally and it will take sometime to arrive from ebay, so, can someone please help me with another solution?

Thank you so much in advance

 

What beside you load (or that this)? What current and what voltage? Whether that galvanic uncoupling?

 

The load is a basically a micro, an esp8266, so the whole circuit runs at 5V and it draws no more than 200mA, the thing is that the supply are batteries and the "deep sleep" mode of the micro uses around 18mA which is a lot to run under batteries and mantain more than a few days, reason why we want to completly disconnect the power supply (open the circuit) when the reed is closed.

 

A Normally closed reed switch?? Thats a new one on me. All reed switches I have ever come across were normally open till they came near a magnet.
Anyway the best way is to use the switch to drive a relay. Then you can do whatever you want with the relay contacts.

 

What beside you load (or that this)? What current and what voltage? Whether that galvanic uncoupling?

 

Haha..I thought the same, I had never used a NC reed but is what I have
The thing with the relay is that I will have to continousy energize the coil and again it will drain the batteries faster, reason why I want to somehow "invert" the reed.

 

See

 

Haha..I thought the same, I had never used a NC reed but is what I have
The thing with the relay is that I will have to continousy energize the coil and again it will drain the batteries faster, reason why I want to somehow "invert" the reed.

You may try to replace the reed switch with one like this one that has both NC and NO contacts on one side. US$2.74 from Mouser.

 

Get a NC or changeover reed switch...


http://m.ebay.com/itm/HQ-3-Pin-2-5x...%3A94e715c815a0a786f5ff2ba8ffe282e4%7Ciid%3A1

 

Sounds like you have a Form A reed switch which is Normally Open and closes when a magnet is applied.
These are quite common and are widely used.

You would like to use a Form B reed switch which is Normally Closed and opens when a magnet is applied in order to put the system to sleep and consume as little as possible energy.

A form A reed switch would consume energy in the 'sleep' mode, but in comparison to the 18ma energy budget, is this really significant?. The internal pull up resistance for the ESP8266 is 30k to 100k. I would think you could cause a logic level change to occur at a GPIO of your choice when the Form A reed switch goes from open to closed for a lot less that any significant fraction of your 18ma while sleeping energy budget.

On the other hand, if you wanted the 'best of both worlds', you may want to consider a form C as in post #8.
You could detect a circuit fault much easier, as the integrity of the connection between the reed switch and the processor could be monitored.

I am also sure that you have found that Form A devices are much more available and significantly cheaper than the Form B parts.

 

Oliver: Seems you have some concept wrong on your schematic with the reed switches in parallel to the load. Should be series like :

(+)------------------openreed----------------------------deenergized---------------------------(-)

(+)------------------closedreed--------------------------energized------------------------------(-)