Led gun cabinet lighting

[daiashthomas]

My name is Ashley, I live in the UK, I work with alarm systems but have not worked at a component level for quite sometime.

I have a variety of bit at my disposal and have retro fitted my gun cabinet with a 12vdc led strip light.

The Magnetic contacts I use in work are what we call normally closed for example when a door is in its closed position and magnet is within range, the reed switch is closed.

Basically this would normally mean that the light would be on when the door is closed ha ha.

So I'm using the reed to switch the negative to control a relay to inturn switch the positive to feed the LED strip.

I have reversed this also so the positive is switching the relay through the magnetic reed, but on both circuits the 12v power supply is buzzing when the door is closed.
I have tried a different supply in both circuits too, but it still buzzes.

Could it be that I need some type of diode or current limiting resistors in the circuit somewhere?


I was only trying to use a magnetic contact, as Trying to position an actual mechanical push to break switch inside the cabinet is going to be an absolute nightmare to position and secure in place.


Thanks in advance!

 

[daiashthomas]

I've been tinkering for last couple of hours, and upped the voltage to 13.5vdc and used a double pole relay to switch the +ve and -ve off to the led strip and this has solved the issue. Must have been something to do with voltage drop through the reed maybe?

 

[123jack]

sounds a bit complicated for a lightswitch on a cupboard door to me.
Is there some reason you cant just use a pushbutton switch?

 

[daiashthomas]

Ha ha, it probably is complicated for a simple cabinet light switch, but the issue I had was trying to mount the push switch and to have it in the right position when the door closes, as it's a gun cabinet there's no way of being inside when the switch engages to know exactly where to mount it.


And the way the door closes and the way the door frame is on it I would've had to made brackets and messed around for a lot longer.

At least with an alarm system magnetic contact, the tolerance is far greater and I literally stuck the magnet and reed/contact in there.

Plus I already had all these components to hand.

 

[betwixt]

For that kind of application I use a lever microswitch. Most are change-over types so you can them to turn the lights on with the door open or closed by swaping one connection. The lever gives you plenty of adjustment range and minimal mechanical resistance.

If you want to do it electronically, use the magnetic switch as before but wire it to the gate of an enhancement mode MOSFET (cheap and hundreds of types to choose from) so it works to reverse the switch logic. It only needs one resistor and the MOSFET to build it:

Source pin to ground (negative supply), LED chain between the Drain pin and +12V, so it's like the MOSFET is where the magnetic switch was originally. Then wire a 100K resistor betwen the Gate pin and +12V and the magnetic switch between the Gate and ground. With the switch (and door) open the gate voltage will be pulled high by the resistor which makes the MOSFET conduct and the LED turn on. When the switch closes, the gate voltage is grounded and the switch turns off. So the switch action is effectively reversed

Brian.

 

[daiashthomas]

I didn't have any lever switches laying about, so made use of what I had, seems to be working great now, I'll probably pickup a lever switch though and ditch the relay which I'm only using as the reed I have needed to be the other way round.

Thanks.

For that kind of application I use a lever microswitch. Most are change-over types so you can them to turn the lights on with the door open or closed by swaping one connection. The lever gives you plenty of adjustment range and minimal mechanical resistance.

If you want to do it electronically, use the magnetic switch as before but wire it to the gate of an enhancement mode MOSFET (cheap and hundreds of types to choose from) so it works to reverse the switch logic. It only needs one resistor and the MOSFET to build it:

Source pin to ground (negative supply), LED chain between the Drain pin and +12V, so it's like the MOSFET is where the magnetic switch was originally. Then wire a 100K resistor betwen the Gate pin and +12V and the magnetic switch between the Gate and ground. With the switch (and door) open the gate voltage will be pulled high by the resistor which makes the MOSFET conduct and the LED turn on. When the switch closes, the gate voltage is grounded and the switch turns off. So the switch action is effectively reversed

Brian.