Normally Open Garage Door Sensor - Need Normally Closed. How to "convert" ?

[gaillimh]

Hi

I have found this thread previously which mentions the above but is a little different so please excuse mods if this seems like duplication.

I have a Wireless Magnetic Switch on my Garage Door - this comms with my alarm system.
The Wireless Mag can take an external input from NC sensor and can also "alert" on trigger of that external sensor.
I bought a Garage Shutter door sensor ( similar **broken link removed**) except is NO.

I would like the simplest solution to convert from "NO to NC" ( so that when the trigger occurs on Shutter door , it sends "open" via Wireless Mag.

Thanks in advance!

 

[tpetar]

Re: Normally Open Garage Door Sensor - Need Normally Closed. How to "convert" ?

Use this as simplest way and problem is solved :wink: :



You can easily adjust resistor for 12V. And for optocoupler You may use 4N35,...
Also this give You very small consuption of current, only few mA is needed, and You got isolated sensors from centrale (VERY IMPORTANT FOR SECURITY)!!!!

Consider that high number of alarms sensor allow only 10-20mA draving of current on output contacts Its not enough for relay.

 

[kak111]

Re: Normally Open Garage Door Sensor - Need Normally Closed. How to "convert" ?

Connect your Garage Shutter door sensor in place of 2-wire prox. sensor
relay contacts have NO & NC

 

[gaillimh]

Re: Normally Open Garage Door Sensor - Need Normally Closed. How to "convert" ?

Hi ,

Thank you for responses.

because there is no power used with garage door Im a little confused as to how it fits together in this case kak111? Have you a suggestion on relay I could use?

@tpetar - using the NO option. Does this mean that OptoIsolator shows NC and then open on trigger?

Thanks again!

 

[tpetar]

Re: Normally Open Garage Door Sensor - Need Normally Closed. How to "convert" ?

On my illustration :

Left circuit shows NO - When given contact in sensor You will get conduction in output of optocoupler.

Right circuit shows NC - When connections is lost (opened), on output from optocoupler You will get contact. Its NC to NO conversion.


If You look better on right circuit You can use also NO to NC. If sensor is NO on output of optocoupler You always get contact (NC), if on sensor give contact situation is changed on output of optocoupler You get NO!

I edit picture for better explaining, here it is :



For 12V use 10K between plus pole and transistor base. Transistor may be any small for signal purposes BC546.

 

[gaillimh]

Re: Normally Open Garage Door Sensor - Need Normally Closed. How to "convert" ?

Thank you for your images , I have added my own here to further ensure I have understood your diagram , because you have 3 scenarios and want to be sure I understand.

Firstly , when the door is closed , the Switch is NO mode. The output of optocoupler shows NC



When the door is opened , the trigger closes on the door sensor and the output of the optocoupler goes open , thus triggering ALARM.



Are my assumptions correct using diagrams above? ( using cut out from yours )

Thanks in advance!

On my illustration :

Left circuit shows NO - When given contact in sensor You will get conduction in output of optocoupler.

Right circuit shows NC - When connections is lost (opened), on output from optocoupler You will get contact. Its NC to NO conversion.


If You look better on right circuit You can use also NO to NC. If sensor is NO on output of optocoupler You always get contact (NC), if on sensor give contact situation is changed on output of optocoupler You get NO!

I edit picture for better explaining, here it is :

View attachment 63168

For 12V use 10K between plus pole and transistor base. Transistor may be any small for signal purposes BC546.

 

[tpetar]

Re: Normally Open Garage Door Sensor - Need Normally Closed. How to "convert" ?

I write at each of three illustration their funcionality.

1. Optocoupler output is normaly open no conduction of current when switch is open. When switch is closed then output on optocoupler conduct current.

2. When sensor switch is normaly closed, then on output of optocoupler no current flow. When switch is open on output of optocoupler current flow.

3. Sensor switch is normaly open, output of optocoupler normaly have current flow. When switch closed then current stop flowing on output of optocoupler.


I didnt find apropriate datasheet for Your magnetic sensor. Tell me when door is close in what state is reed? (NO or NC)?

I supose that You have following states :

When door is closed switch is open.​

When door is opened switch is closed.​

You say that You need NO to NC. Based on that You should use third variant of circuit.

If You look better second and third circuit are the same. Only difference is on state of sensor. Make that circuit and try, You cannot miss.

 

[kak111]

Re: Normally Open Garage Door Sensor - Need Normally Closed. How to "convert" ?

I bought a Garage Shutter door sensor ( similar here ) except is NO.

NO Normally Open >> without magnet switch is open

1. Idea
Look if you can open sensor.
Look if inside there is small glass tube with short wires in both ends ,
this is reed-switch.
You can buy it separately as NO or NC and change it. ( Price maybe 1$ )

Reed switch - Wikipedia, the free encyclopedia

2. Idea
You can test this first with ohm-meter.

 

[gaillimh]

Re: Normally Open Garage Door Sensor - Need Normally Closed. How to "convert" ?

Hi Kak ,

v v interesting and great graphics - I hadnt seen this post.
Changing the reed might be the simplest idea completely.. Im a bit wary of diving into opto isolators etc for now

Thanks again to Kak and tpetar for assistance!

NO Normally Open >> without magnet switch is open

1. Idea
Look if you can open sensor.
Look if inside there is small glass tube with short wires in both ends ,
this is reed-switch.
You can buy it separately as NO or NC and change it. ( Price maybe 1$ )

Reed switch - Wikipedia, the free encyclopedia

2. Idea
You can test this first with ohm-meter.

View attachment 63241