Magnetic switch connection problem.

[[email protected]]

Hi to all.
I have a simple(I think) problem that I'm hoping someone can
help me with.
I want to connect a remote transmitter / receiver pair ( garage door
opener type thing) to an alarm system magnetic switch.When the door/
window is opened it sends a signal to the receiver and activates the
relay.
Hope I'm getting the idea across.
I only have normally open switches. If the door/window is closed and
the magnet is near the reed switch it is CLOSED.
Does anyone have any idea how I can connect the xmitter to this
arrangement so that it is turned on when the switch becomes open.
It must draw no power while closed.(battery operation)
The obvious answer is use a switch that is open when near the magnet
and closed when moved away(N/O) , and connect this to the button of
the xmitter , But I don't have this type of sensor.
My initial idea was to connect the xmitter from Batt+ to gnd through
a PNP transistor(emitter) , collector to GND. The base connected to
Batt+ via mag switch and the base to GND via a resistor.The switch
keeps the pnp off until it opens and the resistor turns the transistor
on.Problem it the constant current draw via the switch and resistor.

Any clever ideas how to get this arrangement to work?
Hope I'm not being to vague in my description.

Cheers
Rob

 

[John Fields]

Hi to all.
I have a simple(I think) problem that I'm hoping someone can
help me with.
I want to connect a remote transmitter / receiver pair ( garage door
opener type thing) to an alarm system magnetic switch.When the door/
window is opened it sends a signal to the receiver and activates the
relay.
Hope I'm getting the idea across.
I only have normally open switches. If the door/window is closed and
the magnet is near the reed switch it is CLOSED.
Does anyone have any idea how I can connect the xmitter to this
arrangement so that it is turned on when the switch becomes open.
It must draw no power while closed.(battery operation)
The obvious answer is use a switch that is open when near the magnet
and closed when moved away(N/O) , and connect this to the button of
the xmitter , But I don't have this type of sensor.
My initial idea was to connect the xmitter from Batt+ to gnd through
a PNP transistor(emitter) , collector to GND. The base connected to
Batt+ via mag switch and the base to GND via a resistor.The switch
keeps the pnp off until it opens and the resistor turns the transistor
on.Problem it the constant current draw via the switch and resistor.

Any clever ideas how to get this arrangement to work?
Hope I'm not being to vague in my description.

 

[[email protected]]

---
Use a bias magnet to keep the switch closed when the window is open
and place it so that when the window approaches the switch the
magnet on the window distorts the part of the bias magnet's field
affecting the switch ,allowing the switch to open.

Thanks for the tip John , but it still does not help me. I probably
did not explain myself well. How can I connect the switch so that when
it opens the xmitter gets powered. I'll short the button on the
xmitter so that when power is applied
it transmits.

Cheers
Robin

 

[ehsjr]

Thanks for the tip John , but it still does not help me. I probably
did not explain myself well. How can I connect the switch so that when
it opens the xmitter gets powered. I'll short the button on the
xmitter so that when power is applied
it transmits.

Cheers
Robin

The real issue lies in exactly what you said:
"The obvious answer is use a switch that is open when near the
magnet and closed when moved away(N/O) , and connect this to
the button of the xmitter , But I don't have this type of sensor."

John's suggestion converts the sensor you do have into the
sensor you don't have.

It provides the function you want by modifying the
switch, not the circuit.

Ed

 

[[email protected]]

The real issue lies in exactly what you said:
"The obvious answer is use a switch that is open when near the
magnet and closed when moved away(N/O) , and connect this to
the button of the xmitter , But I don't have this type of sensor."

John's suggestion converts the sensor you do have into the
sensor you don't have.

It provides the function you want by modifying the
switch, not the circuit.

Ed- Hide quoted text -

- Show quoted text -

Ahh , got it now. Thanks for the help.
Cheers
Robin

 

[Jamie]

Hi to all.
I have a simple(I think) problem that I'm hoping someone can
help me with.
I want to connect a remote transmitter / receiver pair ( garage door
opener type thing) to an alarm system magnetic switch.When the door/
window is opened it sends a signal to the receiver and activates the
relay.
Hope I'm getting the idea across.
I only have normally open switches. If the door/window is closed and
the magnet is near the reed switch it is CLOSED.
Does anyone have any idea how I can connect the xmitter to this
arrangement so that it is turned on when the switch becomes open.
It must draw no power while closed.(battery operation)
The obvious answer is use a switch that is open when near the magnet
and closed when moved away(N/O) , and connect this to the button of
the xmitter , But I don't have this type of sensor.
My initial idea was to connect the xmitter from Batt+ to gnd through
a PNP transistor(emitter) , collector to GND. The base connected to
Batt+ via mag switch and the base to GND via a resistor.The switch
keeps the pnp off until it opens and the resistor turns the transistor
on.Problem it the constant current draw via the switch and resistor.

Any clever ideas how to get this arrangement to work?
Hope I'm not being to vague in my description.

Cheers
Rob

Run a solar cell on the roof to keep batteries charged.
Make sure it's hard to get to.
Use a MOS Type switch which requires very little current
to operate the gate and you then simply short the bias source
with your switches in series, one end of the string to common and
the other end to the input sensor..
Look for Logic FETS, HexFets ring a bell.
they have many. you need to look at the turn off/ON resistance etc..