# Door sw : circuit need to change function

Discussion in 'General Electronics Chat' started by Hubert Wagner, Mar 8, 2015.

1. ### Hubert Wagner Thread Starter New Member

Mar 8, 2015
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Hello List :

Here is the URL to a (sliding) door switch I’d like to use to activate a closet light.

This switch design is ideal because it can be mounted in a round hole drilled in the door frame. And the contacts go straight back rather than sideways so do not interfere with mounting the switch.

Unfortunately, it appears the switch interrupts the circuit when the plunger is down, that is when the door is closed and vise versa.

Is there a way to rig this switch so it operates the other way around. So when the door is closed and the plunger down the light circuit is made?

I see a possible method here :

Using a transistor as a switch.

However, although I understand the circuit diagram in a general way, I don’t know enough to build the thing. Power to the light will be 12v for example. Can the current which switches the power to the light off be from the same 12v source. I guess not. But then the diagram appears to suggest they are somehow connected.

The above will give you a fairly clear idea of my level of knowledge !

All suggestions welcome : Regards Hubert Wagner

PS : Incidentally, the house I've designed and am presently building is a traditional Japanese house, hence the sliding doors.

2. ### MikeML AAC Fanatic!

Oct 2, 2009
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Compare the current through the simulated lamps I(R2) and I(R4) in the two circuits:

The only reservation I have is that the switch is not rated for low-current, non-inductive DC switching, and its reliability in this application may be suspect.

3. ### Hubert Wagner Thread Starter New Member

Mar 8, 2015
6
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Hello Mike :
Would the switch be dangerous used in this way? If it was merely unreliable, what would this mean? Would the switch need to be replaced from time to time or merely that sometimes it would fail to operate?
It appears the power for the circuit all comes from the main source. Is that correct?
In the cast where the switch is open, what does "b" signify?
I assume the resistor 150 ohm?
I would built two circuits for each closet. One for each door but supplied by the same 12v transformer.

Regards : Hubert

4. ### MikeML AAC Fanatic!

Oct 2, 2009
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The current rating of the supply determines how many lamps (total, at one time) you can run.
"b" is just a way of labeling the base of the transistor so I could see which node in the printout was the base.
Yes, but in calculating the power dissipation, it comes out close to 1W. This is wasting too much power, and generating too much heat when the light is not even on, so I am going to suggest a change in the circuit: (see below)
I would build one circuit per closet, but wire two switches in series. If either switch opens, that turns on that closet's lamp.

Here is the revised circuit which wastes much less power when the lamps are off. The resistors can be rated at 1KΩ 1/4W.

5. ### MikeML AAC Fanatic!

Oct 2, 2009
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Another approach: Try this EBay search.

Any of these switches that are advertised as "Normally-Closed" could be used to directly switch the lamps without any transistors... A "normally closed" switch is opened by the closed door. When the door slides away, the switch closes.

If you need two switches per lamp, then wire two Normally-Closed switches in parallel so that opening a door causes either switch to turn on the lamp.

Last edited: Mar 8, 2015
6. ### Hubert Wagner Thread Starter New Member

Mar 8, 2015
6
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Hello Mike :
I've been looking for "normally closed" switch for some time. I've not found any that are as easy to fit. The eBay items would require a lot of complicated chisel work on the frame. Drilling a hole is a much more practical solution. The switch needs to be cylindrical.
I note your remarks about energy dissipation. Can this be resolved? Or are you saying the original switch cannot be made to operate efficiently with a transistor?

"I would build one circuit per closet, but wire two switches in series. If either switch opens, that turns on that closet's lamp".

I don't understand. The second circuit shows two lamps, rather than one lamp and two switches.

Regards : Hubert

Jul 18, 2013
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Have you looked at the burglar alarm type switches for windows and doors?
These consist of a small magnet installed on the moving part (window/door) and the other a reed relay switch, N.C. non contact to activate etc.
Also Hamlin make a small compact version of these.
Max.

Sep 17, 2013
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Jul 18, 2013
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10. ### MikeML AAC Fanatic!

Oct 2, 2009
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Going back to the original switch which interrupts the circuit when the plunger is down, with the addition of the second transistor in the Darlington configuration I posted in #4, the standby power goes to a few mW, so that solves that problem, and eliminates the need for a high power resistor.

You implied that the closet has two sliding doors. Opening either the right side door or the left side door should turn on a single lamp.

So,
You have one lamp per closet.
You have one inverter circuit (a 1K resistor, a 2n3904, and a 2N3055) per closet, serving two switches wired in series, either switch turning on the light.
You have two of the original switches per closet, one for each half of the sliding door.
You have as many inverter circuits as there are closets.
You have one common power supply (one per house).

The circuit I posted in #4 is still a comparison between what happens in the inverter circuit with a closed switch vs an open switch. I just happened to draw it sharing one power supply between both inverter circuits. When you wire the closets, connect the right side and left side switches in series before connecting the resulting two wires to the inverter circuit.

Jun 22, 2012
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12. ### Hubert Wagner Thread Starter New Member

Mar 8, 2015
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Hello Dodgydave :
(Interesting name)
Thanks for the suggestion. I need a switch which can be fitted by drilling a hole. And the contacts need to be inline with the body of the switch. Many switches have the contacts coming out the side.
Regards : HW

13. ### Bernard AAC Fanatic!

Aug 7, 2008
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You mention " transformer ", with any semiconductor switching or LED lights, the power supply needs to be DC. The plunger switch can be used to operate a power FET with either NO or NC contacts. With new construction ,would suggest LED light fixture.

14. ### MikeML AAC Fanatic!

Oct 2, 2009
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Hubert,

I just went and reread your post #1. I think you are confused. Look at the diagram:
If the switch you linked to in your post #1 (data sheet here) is mounted in the door jamb such that the door pushes on the plunger when the door is closed, the switch will be closed. When the door is open, the switch will open.

So your wording is backwards. You said: it appears the switch interrupts the circuit when the plunger is down. You should have said: it appears the switch interrupts the circuit when the plunger is up. However you correctly determined that you need to invert the switch function.

The circuit I posted turns off the transistor and the lamp when the door is closed by shorting the base of the first transistor when the switch is closed (door closed). When the switch is open (door open), the current that flows in the 1K resistor turns on the transistors, turning on the light.

15. ### Hubert Wagner Thread Starter New Member

Mar 8, 2015
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Hello Mike :
Thank you for your patience. (I must say I was amused by your remark that I'm confused. I would reply, "You don't say"!
(I imagine someone showing me how to turn on a light and then, noting my puzzled expression, ask me if I'd like him to run through it again).

Still, I seem to be making progress. Now I know how the switch operates.
OK. The two switches are wired in series. I more or less understand what's happening.

Now I'm not sure how to connect the switches to the circuit. Should these components be put on some sort of board?

Regards : Hubert

PS : Bernard suggested LED lights. My aim is to use these as much as possible.
And thank you the others I've not answered directly.

16. ### MikeML AAC Fanatic!

Oct 2, 2009
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I was using Lamp as a generic description of something that shines when current goes through it; it could be a LED or an incandescent bulb, matters not which. If using LED lamps, they may have a polarity that must be observed.

I am assuming that you are getting "12V LED lamps", which include current ballasting internally, as compared to a bare LED component, where there is some extra circuitry required to make them work.

You should post a link to which LED lamp assembly you intend to use, and we will look at it... It would be best if you could do that sooner, rather than later, because I need to know how much current the LED lamp takes, probably much less than an incandescent lamp.

As to a proposed layout, you require something like this:

where the Inverter Board is wired up on a piece of Vector Board, or Vero Board (electronic breadboard) like this: Note the correspondence between the pin names and the external connections to them.

I would mount the Inverter board close to the Light fixture. Mount the door switches as required in the door jamb and mount the remote power supply (to be shared with other closets and possibly other LED lighting) where convenient.

Last edited: Mar 9, 2015
17. ### Hubert Wagner Thread Starter New Member

Mar 8, 2015
6
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Hello Mike :
I have no experience of using LED lights. I'm still planning the lighting for the house. This 9 watt lamp appears to be suitable for a closet. It comes with a transformer.
http://www.ledhut.fr/led-encastrabl...tt-slimline-high-output-led-ceilinglight.html

The closets are 90 x 180 cm. So the switches are 180 cm apart and the ceiling light about 60 cm above both and 40 cm in from the doors. The house power is 240v. Each light would have a small 12v transformer. So the electronics would go between the light and the transformer. I could put the Vector Board into a junction box above the ceiling. I'd use the standard 1,5 mm wiring for the 12v circuit. Does all this sound reasonable?

The other possibility is 14 watt LED strip.
https://www.simplelighting.co.uk/ip65-high-power-warm-white-led-strip-13920/
100 cm would fit the closet and provide 1080 lumens.
https://www.simplelighting.co.uk/15-watt-led-driver-transformer/
This approach is attractive because the light is spread out and installation is simplicity itself.
I plan to buy some strip to experiment.

Regards : Hubert