Maker Pro
Maker Pro

Proximity detector/switch

Marsh

Dec 29, 2014
3
Joined
Dec 29, 2014
Messages
3
Hello--I am a new member of this forum, in fact I joined to ask this question.
I am trying to determine what type of device I would need to act as a switch or trigger by moving it to within 6 inches of another component. I don't know whether both would have to be powered, or if one could be of a non-powered nature, such as a magnet. Both components need to be rather small in size, say the size of a wristwatch or smaller. I know very little about electronics, and any help would be greatly appreciated. Marsh
 

Gryd3

Jun 25, 2014
4,098
Joined
Jun 25, 2014
Messages
4,098
Hello--I am a new member of this forum, in fact I joined to ask this question.
I am trying to determine what type of device I would need to act as a switch or trigger by moving it to within 6 inches of another component. I don't know whether both would have to be powered, or if one could be of a non-powered nature, such as a magnet. Both components need to be rather small in size, say the size of a wristwatch or smaller. I know very little about electronics, and any help would be greatly appreciated. Marsh
Only thing I can think of is IR.
Same LED's that are in your TV Remote.
Game Boy Color devices used (... attempted to use ...) IR as a near communication device.
Older laptops had this too. Range was not too good, but 6 inches should not be a problem. Sunlight, and other IR sources will create interference however...

Other than that... Ultrasonic would be too large, and radio detection of range that small is beyond my skill-set.
 

Marsh

Dec 29, 2014
3
Joined
Dec 29, 2014
Messages
3
Only thing I can think of is IR.
Same LED's that are in your TV Remote.
Game Boy Color devices used (... attempted to use ...) IR as a near communication device.
Older laptops had this too. Range was not too good, but 6 inches should not be a problem. Sunlight, and other IR sources will create interference however...

Other than that... Ultrasonic would be too large, and radio detection of range that small is beyond my skill-set.

Thanks so much for that input--the size is key here. Also the cost would have to be under a couple of hundred bucks to be commercially feasible.
 

hevans1944

Hop - AC8NS
Jun 21, 2012
4,878
Joined
Jun 21, 2012
Messages
4,878
Funny you should ask this. I have an application in mind, inspired by all the personally-worn electronics (watches. fitness monitors, etc.) appearing on the market lately. There are several possible solutions that I am considering. One of the simplest is a bracelet that uses near-field communication to activate a resonant tuned LC circuit and detect the energy absorbed. The ubiquitous anti-theft tags found on high-value merchandise (such as compact discs) work on this principal. I am somewhat given pause by the realization that the "screening" devices used at retail store exits are huge! OTOH, RF IDs can easily fit in a key fob, or a badge, or on one of my credit cards, so I know that the technology exists to do what I want.

A wrist-band transmitting in a GHz ISM band would probably work but I am concerned about battery life. Better would be a two-way near-field communication between a powered target device and a mostly inactive wristband. Bringing the wristband close to the "antenna" of the powered device would "wake up" the electronics in the wristband and start an exchange of validation information. I think these devices already exist, for example in the form of electronic badge entry-control systems. The badges may even "sip" power from the near-field emissions to enable their RF response.

The Dayton Amateur Radio Association (DARA), of which I am a member, issues key fobs for electronic locks controlling entry to clubhouse facilities. You bring the fob to within an inch or so of the transmitter/receiver mounted near the door to activate the lock. No power necessary (as nearly as I can tell without destroying the fob) in the fob itself.

73 de AC8NS
Hop
 

Marsh

Dec 29, 2014
3
Joined
Dec 29, 2014
Messages
3
Interesting possible solutions, all. I am thinking another one might be a small metal detection application--they can be fairly small, such as devices used to find nails in walls, or hand wands used in law enforcement. Garrett makes one called the Pro-Pointer that I
am going to test in the task at hand.
 

73cat

Dec 30, 2014
7
Joined
Dec 30, 2014
Messages
7
Funny you should ask this. I have an application in mind, inspired by all the personally-worn electronics (watches. fitness monitors, etc.) appearing on the market lately. There are several possible solutions that I am considering. One of the simplest is a bracelet that uses near-field communication to activate a resonant tuned LC circuit and detect the energy absorbed. The ubiquitous anti-theft tags found on high-value merchandise (such as compact discs) work on this principal. I am somewhat given pause by the realization that the "screening" devices used at retail store exits are huge! OTOH, RF IDs can easily fit in a key fob, or a badge, or on one of my credit cards, so I know that the technology exists to do what I want.

A wrist-band transmitting in a GHz ISM band would probably work but I am concerned about battery life. Better would be a two-way near-field communication between a powered target device and a mostly inactive wristband. Bringing the wristband close to the "antenna" of the powered device would "wake up" the electronics in the wristband and start an exchange of validation information. I think these devices already exist, for example in the form of electronic badge entry-control systems. The badges may even "sip" power from the near-field emissions to enable their RF response.

The Dayton Amateur Radio Association (DARA), of which I am a member, issues key fobs for electronic locks controlling entry to clubhouse facilities. You bring the fob to within an inch or so of the transmitter/receiver mounted near the door to activate the lock. No power necessary (as nearly as I can tell without destroying the fob) in the fob itself.

73 de AC8NS
Hop
Great answer, I like it.
 
Top