hi chris.
i was given this topic 'innovations for special people' for my project.i
picked up this idea from this product,
http://www.cobolt.co.uk/cobs/product.asp?dept_id=2&pf_id=Jug
i prefer using the visually detect the position of a floating object
method.my kettle has this floating object at the side to indicate water
level.so i have to put sensors on the outside of the floating indicator.i
think this method does not need any device at the inside of the jug.
how about the electro-optic type sensor?is it expensive.i found it on this
site.
http://www.gemssensors.com/content.aspx?id=282
This little ASCII diagram shows the idea behind the Gems opto sensor
you link (view in fixed font or M$ Notepad):
|
| Photo
| | Trans.|
| | LED - -|
| | ->|- \ ^ |
| | | --- |
| | | | |
| | V | |
| | | ^ |
| | | | |
| | | | |
| | | ^ |
| | V | |
| \ | | /
| \ | |/
| \'-->--'
| \ /
| \ /
| \
(created by AACircuit v1.28.6 beta 04/19/05
www.tech-chat.de)
The LED sends light down to the apex of the cone. If there's no
liquid on the plastic, nearly all of the light will reflect off the
inner surface of the cone, and bounce back to the phototransistor as
shown (kind of -- sorry, this is a newsgroup ;-). However, any liquid
will change the optical characteristic, causing most of the light to
go through the clear plastic cone into the liquid. Hence, level
detect.
Now, in order to use this scheme, you'll need several of these
sensors. In addition, these are not rated as food-safe, which means
you can't sterilize the surface without damaging it. Gems makes some
other sensors which will do the job, but they're significantly more
expensive.
If you're trying to do opto level detection on the cheap, you'll
probably be best off with multiple LEDs and multiple photoransistors.
You can look through a clear jug that way. By turning on one and only
one LED at a time, and only looking at the phototransistor output
directly opposite, you can get a clear idea if something is
obstructing the view. And all of the LEDs plus all of the
phototransistors shouldn't cost more than one of these Gems switches.
Looking at the device you linked in the Cobolt catalogue:
http://www.cobolt.co.uk/Catalogue2006.pdf
I get the feeling that it's actually a scale. Note that you have to
calibrate it for different types of liquids, and it's also capable of
measuring solids with user-defined functions. This seems to be the
easiest way to "skin the cat", and I'm fairly sure it's the method
they use.
If you wanted to do this, you'd have to build a scale around a
removeable jug in such a manner that it was watertight, the jug would
rest freely on the scale base when it was resting, and also that the
jug would be removeable for easy cleaning. Not so difficult to put
together, if you've got access to a microcontroller development kit.
Also, the "talking" function could be done with one of the ISD talking
chips without too much difficulty.
Now for the hard part -- fess up. This is a school project, no?
You'll get better advice if you can be clear about what you need.
By the way, it's almost midnight in this time zone -- if you need a
response, I'll try to post again in about 6 or 7 hours.
Good night
Chris