Non-Touch Switch: Finding a Component Solution

[Blenton]

Could anybody point me towards a component that could serve the purpose of a non touch switch.

To explain it better, one that would trigger when an object or hand were to be placed within say a few centimeters away from it - capacitive switches I've seen all work by touch.

Id like an array of 10 or so of these so I don't really want to build something by first principles (otherwise i'd have a slew of components everywhere) so perhaps a specialised IC?

Thanks.EDIT: Also if possible something that is non obstructive so It can't be like a infrared sensor like those in shop alarms.

 

[schip666!]

There are reflective IR sensors like the Fairchild QRB1133 that work at fairly short distances, and the Sharp GP2D12 that measures a distance up to about 50cm. Or you can go with a capacitive sensor plate like the old-timey theramin, but they are not very stable.

 

[mdjensen22]

You can use capacitive sensors but set the sensitivity to work as more of a proximity sensor.

I have used the Cypress PSoC to implement such systems. If this is of interest, you might want to check out the CY3240-I2USB Demo board. It comes with an I2C to USB bridge, so you can see what the sensor is seeing from a program on your computer.

I know Microchip and Atmel all have their equivalent capacitive sensing methods as well.

The only thing that is somewhat concerning for this approach is that you want an array of 10+. Depending on your physical spacing, you might have trouble differentiating between sensors (not sure if that matters in your end application).

 

[vk6kro]

Another thread on this page has the following circuit:

http://electroschematics.com/6161/power-switch-with-infrared-proximity-sensor/

It has a few components in it but it should be cheap enough and work well. It is a clever design that uses a cheap chip in an unusual way.

You just have to mount the transmitter LED and receive phototransistor so that they can't see each other. Then the only signal that can be received is a reflected one.

You could have several close to each other by setting them to different frequencies with R5 and C2.

 

[Blenton]

There are reflective IR sensors like the Fairchild QRB1133 that work at fairly short distances, and the Sharp GP2D12 that measures a distance up to about 50cm. Or you can go with a capacitive sensor plate like the old-timey theramin, but they are not very stable.

The QRB1133 looks like something promising, where do you think I could get a few of these to aus, ebay search came up blank.

In regards to interference, how close are we talking about that the sensors could interfere? Idealy I want the sensor array to be parallel within 3cm of each other.

 

[Blenton]

The QRB1133 looks like something promising, where do you think I could get a few of these to aus, ebay search came up blank.

In regards to interference, how close are we talking about that the sensors could interfere? Idealy I want the sensor array to be parallel within 3cm of each other.

EDIT: found this on ebay http://cgi.ebay.com/QRD1113-Reflective-Object-Sensor-IC-/110566336244?pt=LH_DefaultDomain_0&hash=item19be4466f4#ht_587wt_905

But at $5 a pop, its not too cheap!

 

[schip666!]

Hmm, I got some from: http://www.junun.org/MarkIII/Info.jsp?item=14 at $2.50US
YMMV