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Proximity Switches

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boardy

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Dear all,

I have a project in mind that i'd like to undertake that involves a key component (proximity switch) and i'm not sure if it exists in the form and parameters that i'm after. I have a fairly basic knowledge of component electronics so have done a small amount of research on proximity switches.

My understanding is that there are 4 basic proximity switches:

-Infared
-Acoustic
-capacitive
-Inductive

My requirements are -

A switch that closes a circuit on a series of leds (turning them on) once a distance of 20cm or more has been reached. Or rather that once the leds and circuit come within 20cms range of a particular object that the leds will turn off.

From what i've looked at on proximity switches they appear to work within quite small ranges, i.e. 25mm max.

So my question is, does anyone know of a proximity switch that has a greater range than the ones i've found or any kind of alternative component that might achieve the same result. The smaller the component the better really.

Many thanks for responses in anticipation.
 
I think it might help if you could describe your whole project. For starters, what is moving toward or away from what?

Ken
 
The project is to do with bikes and safety lighting. I'm looking at some kind of wrist strap indicator system. So the wrist strap would have a series of flashing leds and the handlebars would be the contact point. The idea is once you hold your arm up and away from the sensor on the handlebars, the Leds flash and cars will see which way the cyclist wants to turn in poor visibility conditions.
 
The project is to do with bikes and safety lighting. I'm looking at some kind of wrist strap indicator system. So the wrist strap would have a series of flashing leds and the handlebars would be the contact point. The idea is once you hold your arm up and away from the sensor on the handlebars, the Leds flash and cars will see which way the cyclist wants to turn in poor visibility conditions.

Why not a simple 'tilt' switch on the wrist band.?
 
Interesting project!

I see what you mean about the problem with range. Either a device has limited range, or... the range tolerance is ridiculous (varies a LOT with different conditions). IR is pretty much line of sight outdoors, and active both sides - although perhaps you could have a passive relfector on the hamdle bars which, under normal circumstances is close to a IR emitter/reciever (wrist). As soon as the biker moves his/her hand away from it (or tilts it for that matter, ala Erics idea)... it pings, and does what you need it to do.

You could always include a small delay, so it waits for the reflector/oject to be 'out of range' for say, more than a second, before it does anything... that way you don't end up with lights flashing on and off quickly in the rain, or if the rider twitches their wrist. (or scratches their nose/bum).

Actually depending on usage, I'm not sure the range would be a problem providing you use some form of delay/filtering.

What about a small switch on the wristband? the rider moves his wrist back to switch it. Its not a common thing to do with ones hand, and when the arm is being held out to indicate direction, the hand isn't needed for much else.

For a high tech approach, RFID tags can work at that range (inductive), even the passive ones - although they tend to require rather a lot of power (= bigger batteries = weight = big muscley bikers arm) and it seems to be over kill.

One more brain storm - sorry if it seems like I'm hijacking your idea here - eric gibbs idea, with a touch of intelligence. Make the rider flick his wrist twice. A small microcontroller checks how many times the tilt switch is pinged, checks the time between them, and decides if its a valid 'signal'. Like a crude sign language glove reader :)
 
why not have two push buttons on the handle, the indicators could also be placed on the handle, like in motorcycles
 
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