Proximity Sensing

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Hi Everyone!

I am trying to come up with a proximity sensing design that triggers an external interrupt on a MCU in a battery powered system (no need to sense distance). If a hand waves over the device (~<5cm distance), it will trigger a wakeup on the MCU. So I am thinking of a darlington transistor based design. However, the tricky part is that the PCB will be enclosed in an aluminum "wristband", which the user will wear. This might cause some interference - but as long as the waving hand overcomes a set threshold to trigger the interrupt, it's fine.

Any ideas/suggestions on how I can go about designing the circuit?

Thanks in advance!

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Cut a hole to let an IR transistor look out. Rig up an RC filter and a comparator. When an object like a hand at 98 deg F sits in front of the sensor for 1 sec, do your thing.

Imagecraft compiler user

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It seems by using IR, false triggers may occur in case of prolonged sun exposure or body heat. Aluminum conducts heat quite well and may contribute to "backkground" temperatures that lead to false triggers.

What do you think about capacitive proximity sensing or using darlington transistors to sense the presence of a hand?

Thanks!

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Quote:

It seems by using IR, false triggers may occur in case of prolonged sun exposure or body heat.

So - look for "fairly" quick changes, not absolute levels? Perhaps combined with the 98 deg F requisite that Bob talked about?

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atmel touch switches will probably work.You don't actually have to touch, if the sensor area is large enough. You could probably use the aluminium wrist band as the sensor... I did a similar thing with a 'climbing wall'

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Or use a theremin circuit.

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Thanks for the suggestions everyone!

@chartman, Could you clarify 'climbing wall'?

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Quote:

@chartman, Could you clarify 'climbing wall'?

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Interesting, thanks!

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That's the one.... each hold has a touch chip attached to it... very sensitive as it has to detect a foot as well as a hand...

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Remembering this thread it triggered a thought when I was in an airport bathroom this weekend and used a sink that detects when your hands are present. Any idea what type of sensors they use? Same with the toilets/urinals that detect when to flush?

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Johan, you there to catch her if she falls?

Most of the walls in this area require a safety wire.

Ams, most of the automatic airport sinks I've seen have a small window under the faucet, aimed at the user, for IR detection of the human.

Urinals use several techniques, IR, timed, other.

JC

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Capacitive is generally within a few centimeters unless you use a capaciflector...
http://www-cdr.stanford.edu/Touch/previous_projects/capaciflector/capaciflector.html

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Quote:
Johan, you there to catch her if she falls?

Don't think so. What are the chances for a healthy relationship if she is climbing the walls even at the start?

(Re "climbing the walls". Is that expression used in English also? In Swedish it is used about someone who can't stand her current vista, usually on the grounds of being extremely bored or impatient, wanting desperately to get out. Eg. something you say when you've been grounded and tied to home because of a lengthy illness - "I was climbing the walls".)

I just Googled for that photo - that sport is not anything I fancy doing myself. Standing on a ladder three steps up to change a light bulb gives me enough vertigo.

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Yes, it is the same in English.
We might also say someone or something is "driving us up the wall", if it is profoundly annoying, or irritating.

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Bathroom automatic fixtures seem to be IR. Most have a small deep-red to black plastic window.

Jim

 

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Those fake rocks on the climbing wall ar all held in place by bolts. Would a strain gauge on the mounting bolt be enough to detect someone holding or standing on it? Just a thought.

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Maybe.... but sooo expensive :)

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