Reed switch + LEDs + cupboard

Hi All,

Just wanting some advice about a small project I am hoping to set up:

We have a pantry that has 2 sliding doors and is unfortunately in a hallway with very little lighting. There is 5 shelves along the length of the cupboard and it is arbitrarily divided in half by the sliding doors (you can only see at most half the cupboard or the 2 outside quarters).

I am hoping to set up some LEDs on the underside of the shelves that come on only when the doors are open using a reed switch on each door. As both doors can be partially open the whole thing will need to cope with the possibility of all the lights on at once.

Here is what I am thinking of buying and need to know if it will work or if I am way off the mark:

5M of LED lighting strip that can be cut up into 10 x 50cm strips (5 for each side):
http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&item=180851050514
Working Voltage: 12VDC(12V 2A for 5meters 3528 300LED light strip)

12V adaptor:
http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&item=260925910033
Input: 100-240V AC 50/60Hz -Output : 12V 2.0A DC

And the next problem is the Reed switches -
either:
http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&item=160781425423
Rated power: 10W Rated current: 500(mA) Rated voltage: 200(VDC)

or from Jaycar:
http://www.jaycar.com.au/productView.asp?ID=LA5070

The questions I have are:

1. Do I have all the parts to actually make the setup work?
2. Will the DC adaptor struggle as it is rated at 2A and the strip draws exactly 2A?
3. The ebay Reed switches are only rated at 500mA, which I think is not enough and the Jaycar ones don't even list their specs? What should I do?
4. I think I need a 'normally closed' Reed - is that right?
5. Is there a better way to do it rather than Reed switches?


Thanks in advance for the help!

 

You would need a 12v relay to switch the current for the LEDS.
The reed switch activates the relay. The relay switches the current.
You are correct. You would need normally closed reeds.
The way you have explained seems fine to me.

 

Thanks for the replay - my understanding of electronics is fairly basic but supplemented by Google.

It's my thought process that the relay does the heavy lifting for the Reed switch as it can't handle what is running through the circuit - is that right?

If the Jaycar one is rated much higher would a relay still be needed?

Also does that mean the circuit with the reed switches would need it's own power supply?

 

Yeah. That's right.
Just use a relay. It will be better that way.

 

Sorry - added the last question via edit:

Would that mean I need a separate power supply for the reed switches?

Would a 12V 3A relay suffice?

Adding a layer of NO/NC makes my head hurt.
I would want a NC reed and then an NO relay?

 

maybe look at a limit switch instead? depending on what you choose may mitigate the need for a relay, and it becomes a simpler circuit.

you could always grab a slightly larger supply in case you like the idea and choose to add to it later.

 

Oh yeah limit switch looks perfect. I like simple too

 

I would stick with the reed switch they are pretty reliable. Limit switch's seem a lot more prone to issues in my experience.

Most reed switch's are NC when the door is closed but you can get NO and in your situation that would be better.
That way the relay will be only powered when you open a door.

So X doors with each reed switch in parallel. When one door opens it activates the relay.
Relay closes a NO contact to turn on light.
Can use the same power supply for the reed switch circuit and lights.

 

The only other concern about reed switches is the distance at which it senses the magnet - if the door is *slightly* ajar it might turn the light on. (could probably be overcome with a magnet on a spring setup as I assume most magnets would work).


If I was to go limit switch it would probably be:
http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&item=160778191159

I can see mounting this on the architrave of the door and when the door slides past it pushing the roller closed. I take it that with 3 pins the whole NO/NC thing is a non-issue for limit switches (just wire it correctly)

I can't find any limit switches on the jaycar website - are they known as something else?

 

Ok I think this is how I need to wire it.

Please ignore the TERRIBLE drawing - the fact that it is not the right symbols, the right connections to the switches etc. This is just a mud map :S

S1 and S2 are reed switches
RLY1 and 2 are relays
The LEDs are well, LEDs
Vsl is the 12V power supply.

 

I am aware that diagram would make electronic engineers everywhere weep.

 

Most reed switch's take a cm or so before they change state.

Assuming S1/S2 are going to the coil on your relay and your contact is separated from that S1/s2 feed unlike as drawn your diagram will work.

 

In your diagram, the reed switches are just shorting out the 12v supply.. and the Coil is missing from the relay.. the relay coil should be in series with the Reed switch

but anyway, assuming that correction, as mentioned above you'll need to find a NC (normally closed) Reed switch. i.e closed when not magnetized. OR you need to use the Normally closed contacts on the relay, and have the relay energized whenever the cupboard is closed.. a non ideal situation but would still work of course.

 

Yeah sorry about the wiring on that diagram - didn't quite know how that would go....

I see the suggestion of maybe a bigger power supply should I go for a 5A supply like this:
http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&item=180865534326

Is there a possibility that it will overload it or will it just draw as much as it needs? Is it overkill and is a 2A (yum cha) supply enough?

I am still tossing up between the limit switch and the reed switch - limit does seem easier to implement.

 

This is how I'd do it.


Click to view full size!

The switches are any type of Normally Closed switch that suits the application (reed, push button, limit, whatever).
The relays are ones with the coils rated to the supply voltage, with Normally Open contacts.
You then attach your LED strips to the designated points, if you want a few per 'channel', just hook them up in parallel.

Adding more individual 'channels' is as simple as duplicating what's there as many times as needed.

As for the power supply, a 12V plugpack with a suitable current rating will probably do the job. You'll have to work that out from what and how many LED strips you'll be using.

 

I doubt he wants the lights on with the door closed.
Also having the relays permanently powered is not only an extra waste of power but going to burn them out faster.

Change the reeds to NO and its better.

 

too late for me to work through the logic of NC/NO right now - will re-examine in the morning...

I have decided to go with a 600 LED strip (per 5m) which will give more light - if it is too much I will cut it down or use a dimmer but better too bright than not bright enough. These draw 4A in total so I will go with a 5A power supply.

I realised the limit switch I listed earlier only mentions AC not DC:
http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&item=160778191159

I assume that rules it out?

Other limit switches list DC - 0.6A at 125V which I assume translates to 6A at 12V.
http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&item=160786775070

Also in my ebay travels I came across some spring actuators which looked very interesting as they might better suit a sliding door set up.
http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&item=150796690361

 

Not correct. The reed switches are closed without a magnet (NC), when the magnet is there when the door is closed, the switch opens, turning the relays and hence LED's off.

 

Every time I have brought reed switch's they have come in the sealed state. ie with magnet in position.

 

I would probably go for the Jaycar ones which can be either NO or NC rather than a fixed pair from ebay - just to cover all possibilities.