Looking for tilt alarm circuit design?

[Imp]

I am looking for a simple tilt sensor circuit that will sound an alarm and
that will run off a 9V battery? If anyone could point me to some designs or
a predesign circuit I could buy; I would be most greatful.

Thank you for your time.

 

[Wolfgang Mahringer]

Hi Imp,

I am looking for a simple tilt sensor circuit that will sound an alarm and
that will run off a 9V battery? If anyone could point me to some designs or
a predesign circuit I could buy; I would be most greatful.

A mercury switch can do that:
http://en.wikipedia.org/wiki/Mercury_switch

HTH
Wolfgang

 

[Imp]

Sorry... but that wont work... It can't self set. I am looking to build a
tilt alarm... one that can be set anywhere at any angle and will go off when
moved... A mercury switch can not self level and set at any angle... where a
tilt sensors can be used in a circuit to read and remember the angle and be
design to set-off an alarm when moved. This is the circuit I am seeking.

 

[Spehro Pefhany]

Sorry... but that wont work... It can't self set. I am looking to build a
tilt alarm... one that can be set anywhere at any angle and will go off when
moved... A mercury switch can not self level and set at any angle... where a
tilt sensors can be used in a circuit to read and remember the angle and be
design to set-off an alarm when moved. This is the circuit I am seeking.

Maybe you want a vibration alarm? A mercury switch that can be
rotated?

You could use an (1, 2 or 3-axis) accelerometer to measure gravity,
but that would be expensive and might consume too much power for
batteries even if it was pulsed.


Best regards,
Spehro Pefhany

 

[Lostgallifreyan]

Maybe you want a vibration alarm? A mercury switch that can be
rotated?

You could use an (1, 2 or 3-axis) accelerometer to measure gravity,
but that would be expensive and might consume too much power for
batteries even if it was pulsed.


Best regards,
Spehro Pefhany

The simplest way I know is a vibration switch, like you said, with an SCR
in series with the alarm, and the switch to trigger it. To untrigger it,
you have to momentarily disconnect the supply.

Maplin used to sell a small switch in the UK, and I still have one around,
it is sensitive to small hand movements but insenstive to orientation so
long as it's still. I can't remember the part code though, and I don't
think they sell them now.

It will NOT detect tilt, if applied very slowly, but is that really what
you want? If it is, then you'll have to use three, one in each axis, sum
their switched voltages, then detect the change in the summed output to
trigger the alarm.

 

[Imp]

To make things clear I will not use mercury switchs!!!

I could though use a two axis accelermeter.... I am looking at Memsic 2125
Dual-Axis Accelerometer. With Low current operation: less than 4 mA at 5
vdc... it has Simple, pulse output of g-force for X and Y axis but am have
trouble locating what the X Y output is when moved.

 

[Lostgallifreyan]

Sorry, got confused to who I was answering.. first bit, to the poster I
answered, last bit, to the first poster. Also, meant three mercury tilt
switches (not vibration type).

Also, how much tilt do you want? if it's less than about 45° from
horizontal, and if you want proportional sensing not switching, then maybe
a tiny joystick, mounted upside down, with a small weight on the toggle?
You'll have to experiment with the mass, and the length of toggle
extension, but it's cheap, and might be accurate. You can use op-amp based
comparison to a preset voltage made equal by reading the current value at
will, copying it to a sample and hold (LF412's are good for all these
tasks), and if the thing is moved, the voltage change can be detected.
Adjust sensitivity by gain (in the sensor amp) and hysteresis (in the
comparator stage). You could do this for both axes but you might get good
results from summing them and watching the combined output if it's not
important exactly what degree of movement occured in which axis.

 

[Lostgallifreyan]

Forget my sample/hold, got a simpler idea. Charge a big capacitance.
That way slow changes won't set the alrm off, but fast ones will, and it
won't droop over time, and you get better control of what respose speeds
you want. The current value can be passed to the capacitor via a high
resistance, and to set the device you short that resistance to level the
charge with your signal, then arm the detector, which compares the
capacitor charge with the sensor voltage and shouts if they change.

 

[Lostgallifreyan]

To make things clear I will not use mercury switchs!!!

I could though use a two axis accelermeter.... I am looking at Memsic
2125 Dual-Axis Accelerometer. With Low current operation: less than 4
mA at 5 vdc... it has Simple, pulse output of g-force for X and Y axis
but am have trouble locating what the X Y output is when moved.

Ok, well, we might be able to help you more if you said more about what you
do want. Do you want to stop a thief? Or to stabilise a space station?

 

[Matt J. McCullar]

Sorry... but that wont work... It can't self set. I am looking to build a
tilt alarm... one that can be set anywhere at any angle and will go off when
moved... A mercury switch can not self level and set at any angle... where a
tilt sensors can be used in a circuit to read and remember the angle and be
design to set-off an alarm when moved. This is the circuit I am seeking.

Dunno if this is closer to what you're looking for, but pinball machines
have long used a very simple device to detect a tilt. It's a long, thin
metal rod with a weight on the end of it, surrounded by a conducting ring.
It's essentially a pendulum that can swing in any direction. If the
pendulum hits the ring, the alarm goes off. It's just a big switch.

What's more, you can adjust the sensitivity simply by adjusting the height
of the pendulum. If you want more sensitivity, you lower the surrounding
ring so that the very end of the pendulum will touch it. If you want the
sensitivity to be less, then you move the surrounding ring further up the
pendulum so that it must swing futher before touching.