Sensor idea needed for deadbolt

T Chap

Hey guys. Can anyone suggest a sensor idea that would detect the presence of a stainless deadbolt inside a receiver? There may be a little stray light inside the cavity that receives the deadbolt. I was thinking about the QTI sensor as an option, as it needs to be small. The sensor must be mounted inside the receiver with no mechanical parts. Any suggestions would be appreciated for something easy to do with a Prop.

Thanks

ElectricAye

T Chap wrote: »

...There may be a little stray light inside the cavity that receives the deadbolt....

The QTI has a daylight filter on it, so that might help with the stray light issue. Sounds like a reasonable idea to me.

Phil Pilgrim (PhiPi)

How about a limit switch?

-Phil

T Chap

Thanks for the response. The switch is not workable in this application. I need to find a contact-less method. I ordered the QTI and there is an object for it, maybe this will be a good solution....

markaeric

Or how about a magnet placed in a small cavity drilled out in the center of the deadbolt , detected by a magnetic reed switch?

Spiral_72

a 12mm prox! Bore a 1/2" hole in the door frame into the wall. You'll have to open the reciever up a bit so the metal doesn't interfere

Mike Cook

This might work, never tried it, you would have to test it.

Use the dead bolt as a ‘Gear tooth’. Mount a magnet and the Melexis 90217 Hall-Effect Sensor in the dead bold receiver.

http://www.parallax.com/Portals/0/Downloads/docs/prod/compshop/MLX90217.pdf

ElectricAye

I think T Chap mentioned that it's a stainless dead bolt, and I think some stainless steels aren't nearly as magnetic as regular steel. Would these magnetically-based sensors actually work that well?

T Chap

The thing is that the dead bolt may not end up precisely at the same point every time, it is a long throw and it could get semi-locked. So a switch or magnet idea could fail on some occasions. Ideally, some method to detect the presence of the deadbolt with a high degree of tolerance is needed. Pressure against a switch is not an option. The deadbolt cannot be altered cosmetically, so any concept of modifying it is out as well. The sensor must operate alone in the receiver, which is a small stainless box that fits loosely around the deadbolt in the door jamb. The PING concept would work if space allowed. I have a feeling that the QTI may solve the problem as it can operate over a range of reflections, giving a higher degree of tolerance versus a switch or magnets. Anything else along these lines would be great to know about. Thanks!

Phil Pilgrim (PhiPi)

A transmissive sensor would be more reliable than a reflective one. Mount the light source and sensor in the deadbolt receiver at the top and bottom locations in a horizontal position that represents the minimum insertion depth for a successful lock.

-Phil

T Chap

The transmissive idea is what I need to be safe. I have never used IR before. Can anyone tell me whether there is 'best' method to use? For example, would the concept be to just turn on the LED permanently and have the receiver checking for the presence of IR. Or, would some logic be used such as sending a string to the LED and have a method reading it, avoiding a false read.

Phil Pilgrim (PhiPi)

I there's ambient light, the safest way to go is to use one of those IR remote control receivers like Parallax sells and a modulated IR source. In such close, highly reflective confines, however, some IR may still bounce around and make it to the receiver when the deadbolt is in place. To avoid this possibility, put both the IRED and the IR receiver at the ends of narrow tubes to collimate the light, and use the minimum IRED current required to get a reliable read.

-Phil

T Chap

Thanks Phil!

kwinn

T Chap, if you can put the ir emitter in the bottom of the receiver and the phototransistor in the top it should work well. Most of the ambient light comes from above, not from the floor.