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Very Basic Circuit Question

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tomallen35

New Member
Hi

I have a vibration switch that I had hoped would complete the circuit when moved, but in fact it does the opposite.

My test circuit comprises of a couple of AA batteries in serial, the vibration switch and an LED. How can i make it so that movement of the vibration switch turns on the LED rather than turning it off?

Thanks!
 

Mickster

Well-Known Member
Most Helpful Member
Can you show us a schematic, or pic of how you currently have it set up?

If you can provide a datasheet for the 'vibration switch', that would be more helpful....
 

tomallen35

New Member
Sure. I bought one of each of the non-surface mount switches from here: **broken link removed** (currently using the larger one).

Here's what the circuit currently looks like:

**broken link removed**
 

crutschow

Well-Known Member
Most Helpful Member
Certainly you could connect the switch between an NPN transistor base and ground with the collector connected to the LED and the emitter to ground (-). The other end of the LED is connected to V+ through an appropriate resistor. Bias the transistor with a resistor connected between V+ and the transistor base (resistor value to give a base current about 1/10 of the LED current). That will invert the signal so that when the switch is closed, the LED is off.

This circuit will draw about 10% of the LED current (through the transistor bias resistor) when the LED is off. Is that acceptable?
 

tomallen35

New Member
This circuit will draw about 10% of the LED current (through the transistor bias resistor) when the LED is off. Is that acceptable?
It might be if there is no other reasonable solution. The circuit will always be powered by AA's so battery life is concern.

I can guide you,if I look at the circuit.
I posted one up, but the message is still stuck in moderation as it had a link to the site I bought the vibration switch on it. If it's still not up by the time I get home, I'll repost the diagram without the link.
 
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SABorn

New Member
Depending on the switch, the easy way could be to mount the switch upside down.

A lot of these switches are not much more than a mercury switch which could work upside down in reverse.

Guess we will see when the link shows up.

Pete.
 

tomallen35

New Member
I can tell you that it is a non-mercury, omni-directional switch. While I can't post a link to it yet, if you search google for rapid electronics uk, then use their search engine to find 'vibration', then the top result is what I've got (there are actually 3 different switches there - i bought the 2 non-surface mounting ones as i couldn't tell which i needed!)
 

BrownOut

Banned
It occured to me that it might be a normally closed switch, or else it might have normally closed and normally open connections. How many connections does the switch have? Can you see the letters "NC" and "NO" on any of the connections?
 

Mickster

Well-Known Member
Most Helpful Member
Rapid Electronics page:
**broken link removed**

Datasheet:
**broken link removed**

EDIT:
From the datasheet;
"The time taken to settle depends upon the amount of energy absorbed by the device, the settled state will be random unless mounting attitude is chosen for a n/c output."
 
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tomallen35

New Member
Sorry, I'm pretty rubbish at all of this :)

As I see it - there are 3 mounting points on the switch; 2 pins and the surface of the switch itself.

**broken link removed**

If I connect 1 to B and 2 to A, then the switch is closed when stationary.

If I connect 1 to C and 2 to A, then the switch is random when stationary.

Hope that helps!
 

carbonzit

Active Member
You left an important piece of information out, which is the physical orientation (i.e., up, down or othewise) of the switch, as the documentation appears to say that the "mounting attitude" (position) of the switch is important.
 

BrownOut

Banned
Try connecting 1 to B and 2 to A, then turn the switch upside-down from the way you had it before.
 

tomallen35

New Member
Hmmm, if the orientation is the reason it's not working, then I've got the wrong component :( It needs to work at any orientation and complete the circuit when moved. Any suggestions what I should get as a replacement?
 

carbonzit

Active Member
Well, since you describe the switch as a "vibration switch", it stands to reason that it's probably going to be sensitive to orientation, no?

So what exactly are you trying to sense? What exactly do you mean by "vibration"? Somebody bumping into your car? an earthquake? someone placing an iPod on a table?
 
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Mickster

Well-Known Member
Most Helpful Member
Many years ago, shock/vibration sensors in automotive alarms used to use a piezo disk with an attached weight. This could be used in any orientation.
Not as simple as that alone though....you'd still require something like an OpAmp and other components to detect a trigger and be able to adjust the threshold.
Size of a complete project would also be an issue....

Anyway, I digress. Could this be a better solution and does the LED need to latch when a trigger occurs?
**broken link removed**
EDIT: The datasheet:
**broken link removed**
 
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tomallen35

New Member
It's not specifically vibration, more omni-directional movement - I just don't know what to search for. Basically, I want to be able to close a circuit when there is movement in an object of non-uniform shape (i.e. it can be stationary in potentially any position/orientation).

Essentially, the problem could be solved with a metal spring mounted inside a conductive tube like so:

**broken link removed**

At rest, the spring would be straight, and therefore not touching the sides of the tube. When moved, the spring would flex, touch the surrounding tube and complete the circuit. Sorry, I can't really describe it any better than that :(
 
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carbonzit

Active Member
But that would violate your stated requirements, wouldn't it? If that gizmo were laying on its side, then the spring would be in contact with the side.

I'm sure there's some device made in the world today that satisfies your requirements. I just don't know what.

Perhaps what you want is an accelerometer, like this one from digiKey? ( Datasheet here.) Would require a bit of interfacing, of course.
 
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Mickster

Well-Known Member
Most Helpful Member
It would be more beneficial if you could give us a detailed scenario of what you wish accomplish, leaving nothing out, along with which, if any, actions you require when a trigger occurs, i.e.
"I would like to embed a device in an object (soft toy/rock etc), which detects when it is picked up or slightly moved in any way. I wish to use it as a dog trainer in order to stop my dog from chewing my shoes/digging up my garden etc. etc. Initially, to prove my circuit works, I will be using an LED for indication but eventually I would like to use a buzzer and have it sound for 10 seconds when triggered."

Some things which appear to be initially simple, can end up quite complex once the full requirements are revealed.
 

tomallen35

New Member
Basically, what I'm trying to achieve is a piece of clothing (could be t-shirt, shorts, hoodie, whatever), is moved either while being worn, or just picked up/put down, a series of LED's is lit. The LED's don't need to do anything fancy - no flashing sequence or anything, just light up.

Hopefully that's enough info, but it appears from what people have been saying, it's going to be way more complicated than it's worth...
 
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