I need a special kind of switch

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#1
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Here's my problem.  I need to wake up (and sleep) a battery-powered AVR by closing a switch or some other means, but I can't have any physical contact with the board or anything connected to the board (it will be in a little plastic container).  The container will be about a foot out of human reach, so it may require something on the end of a stick to activate the AVR.  I can't shake or otherwise move the container.  I was thinking maybe waving a magnet by the container and having a reed switch or equiv. on the board.  How would you do it?

 

Oh yeah, cheap is important!

Last Edited: Sat. Feb 27, 2016 - 10:59 PM
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I use reed switch in similar applications. Works well. Zero power. Not CHEAP but not that expensive, either. Absolutely sealed so not subject to corrosion.

 

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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sounds like a school project!

 

You could use a hall sensor, with a magnet.

 

 

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Last Edited: Sun. Feb 28, 2016 - 02:20 AM
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Hall sensors uses lots of stand-by power (for a battery powered device). Reed uses none. Reed switch typically is larger. 

 

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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I like the reed switch concept.

 

But if you are looking for additional ideas, one might also consider a flashlight and a photodiode in a resistor divider setup.

 

JC

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Thats a good idea, if it will be in the dark except when being switched.

 

There is also a fair variety of magneto-resistive switches. They are not zero power but they are pretty low. They are commonly used to detect when the lid of a laptop is open or closed. Hall sensors tend to take a lot more power.

 

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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I agree. The magnet/reed switch combo ticks all boxes (that we are aware of).

Ross McKenzie ValuSoft Melbourne Australia

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ka7ehk wrote:

Thats a good idea, if it will be in the dark except when being switched.

 

If ambient light is a problem then use UV.

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since a  reed switch cost about $0.5 and about $0.2 in real high volume it's hard to beat.

 

but other ways could be a response to a click sound (that is so sharp that power from the receiver will make a start.)

 

or have a wire in the box  and a receiver that react on that (something like a 128KHz receiver). 

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I need to wake up (and sleep) a battery-powered AVR

 and

a click sound (that is so sharp that power from the receiver will make a start.)

so are you saying that the click sound (or the 128KHz transmission) generates enough of its own energy to trigger the unit on... that is there is no standby energy required of the "detector"?

 

Ross McKenzie ValuSoft Melbourne Australia

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so are you saying that the click sound (or the 128KHz transmission) generates enough of its own energy to trigger the unit on... that is there is no standby energy required of the "detector"?

That's what I made of it.  A simple speaker or piezo attached to a PCINT and GND (with a quench diode).  If the sound impulse is loud enough, it would trigger an interrupt.  Not sure how loud it would have to be.  Possible >>very<< loud.

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ki0bk wrote:

sounds like a school project!

Nope, very real-world (but also very unique).  But I can see why somebody could think that.

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joeymorin wrote:

so are you saying that the click sound (or the 128KHz transmission) generates enough of its own energy to trigger the unit on... that is there is no standby energy required of the "detector"?

That's what I made of it.  A simple speaker or piezo attached to a PCINT and GND (with a quench diode).  If the sound impulse is loud enough, it would trigger an interrupt.  Not sure how loud it would have to be.  Possible >>very<< loud.

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valusoft wrote:

I agree. The magnet/reed switch combo ticks all boxes (that we are aware of).

Yes, I'm convinced now.  Next step then is to read up on the sleep modes, etc.  In all the years I've worked with AVR I've never needed that feature before, but because I can't have a real power switch on this device I have to fake it.

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kk6gm wrote:

joeymorin wrote:

so are you saying that the click sound (or the 128KHz transmission) generates enough of its own energy to trigger the unit on... that is there is no standby energy required of the "detector"?

That's what I made of it.  A simple speaker or piezo attached to a PCINT and GND (with a quench diode).  If the sound impulse is loud enough, it would trigger an interrupt.  Not sure how loud it would have to be.  Possible >>very<< loud.

"Let me load this 12 gauge blank cartridge into my starter unit.  Stand back!"

:-)

Not necessarily.  You might get quite a few volts out of tapping a small piezo disc with the end of a pencil.  The AVR pin will present no load, so even a tiny speaker (say, from ear buds) could develop a spike of a few volts when tapped.

"Experience is what enables you to recognise a mistake the second time you make it."

"Good judgement comes from experience.  Experience comes from bad judgement."

"Wisdom is always wont to arrive late, and to be a little approximate on first possession."

"When you hear hoofbeats, think horses, not unicorns."

"Fast.  Cheap.  Good.  Pick two."

"We see a lot of arses on handlebars around here." - [J Ekdahl]

 

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joeymorin wrote:
kk6gm wrote:

 

joeymorin wrote:

 

That's what I made of it.  A simple speaker or piezo attached to a PCINT and GND (with a quench diode).  If the sound impulse is loud enough, it would trigger an interrupt.  Not sure how loud it would have to be.  Possible >>very<< loud.

 

 

"Let me load this 12 gauge blank cartridge into my starter unit.  Stand back!"

 

:-)

Not necessarily.  You might get quite a few volts out of tapping a small piezo disc with the end of a pencil.  The AVR pin will present no load, so even a tiny speaker (say, from ear buds) could develop a spike of a few volts when tapped.

True, a direct tap might do that.  I've got some crystal earpieces like the crystal radio guys use (I use them with tube regens, but that's another story).  I'll try it just out of curiosity, but I already ordered a load of reed switches.

 

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If you're using a reed switch you can forget sleep modes and actually control the power. The method has been described in these forums before - you'll need a transistor of some sort controlled by an output that can keep the power on until it's time to turn off.

On the other hand, sleep may be good enough, or you may need to use sleep for other reasons, so just a suggestion.

 

 

Quebracho seems to be the hardest wood.

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John_A_Brown wrote:

If you're using a reed switch you can forget sleep modes and actually control the power. The method has been described in these forums before - you'll need a transistor of some sort controlled by an output that can keep the power on until it's time to turn off.

On the other hand, sleep may be good enough, or you may need to use sleep for other reasons, so just a suggestion.

 

 

Good point.  I can see how such a circuit would work, so thanks for the tip.

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Out of sheer curiosity, what type -- if any -- of shielding would one need for the rest of the circuit when using a reed switch?

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