On Thu, 12 Mar 2015 07:01:31 +0000, Charlie+ wrote:

On Wed, 11 Mar 2015 19:03:25 -0700 (PDT), wrote as
underneath :
On my old Canon ip4300 printer the ink level can be seen through the
clear plastic of the cartridge,unlike my Epson BX525WD multifunction
printer.

Yep, any (prism) level measurement in the visible spectrum would need
clear cartriges! Nearly all modern OEM carts. are black or an opaque
colour! C+

Not exactly. There are more than a few problems.

Most older cartridges have open cell foam inside to prevent sloshing
in transit. Kinda difficult to design a liquid level sensor that
works in foam. Neither dye or pigment type inks are very conductive,
so that's not going to work.

Some carts don't have any foam and are often clear or at least
translucent. However, they are usually used with dye type inks, which
are optically transparent. So, that's not going to work.

Older HP color carts have 3 colors in one cartridge. 3 sets of
optical sensors in one cart isn't exactly economical or practical.

Optical sensing might work with pigment type inks, but I suspect the
optical transmission characteristics will vary with the color. Also
yellow is nearly transparent.

There is one place where optical sensing works... laser printers. The
toner is optically opaque. Brother printers have windows on each end
of the cartridge. Then the light can be seen through the cartridge,
it's considered out of toner. The problem is they located the windows
a bit too high on some printers. I forgot the model, but one of their
older color laser printers leaves about 25% in the cartridge when it
claims it's empty. The fix is to put some electrical tape over one of
the windows.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558