IR Prox detector with twiat

[Joseph Goldburg]

HI All,

I am looking for ideas for an IR prox detector that can detect
a credit card with 5~10 millimetres or better.

The twsit is it has to be very low current as the device will be
battery powered.

QUESTION

Will IR bounce of all different cloured surfaces of a credit card?


Check my Plan A below.

Regards
Joseph


Plan A

Use a low power micro
Wake up every second and turn IR LED on for 100uS
Listen to output of IR receiver

Loop in 10 cycles (with 1~10mS period)

Trun IR LED On
Check If IR bounce detected in IR Rec

Turn IR LED off
Check If IR rec is OFF

Exit loop if any of the above conditions are false (no card detected)

End Loop

Card detected.

 

[Terran Melconian]

In article <c3cgh0$ebo$1@otis.netspace.net.au>,
Joseph Goldburg <wizard1@SPAMnetspace.net.au> wrote:

Will IR bounce of all different cloured surfaces of a credit card?

I wouldn't be on it. Even if it works on your test cards, some
manufacturer somewhere is going to have used dyes that happen to be dark
at IR.

IR is suitable for detecting things like this only when you can use it
tranmissively (blocked by the card when present), not reflectively. If
you can't put the photodiode (or at least a mirror) on the *other* side
of the card, I think you'll be sorry trying to use IR.

I'd try ultrasonics or capacitative sensing.

 

[GPG]

terran@mit.edu (Terran Melconian) wrote in message news:<c3de8g$2tk$1@means.mit.edu>...

In article <c3cgh0$ebo$1@otis.netspace.net.au>,
Joseph Goldburg <wizard1@SPAMnetspace.net.au> wrote:
Will IR bounce of all different cloured surfaces of a credit card?

I wouldn't be on it. Even if it works on your test cards, some
manufacturer somewhere is going to have used dyes that happen to be dark
at IR.

IR is suitable for detecting things like this only when you can use it
tranmissively (blocked by the card when present), not reflectively. If
you can't put the photodiode (or at least a mirror) on the *other* side
of the card, I think you'll be sorry trying to use IR.

I'd try ultrasonics or capacitative sensing.

The coating will be the reflector. Check some cards

 

[Check It Out]

Isn't the sensing range to be 5-10 millimeters? I could detect a blackhole
at that range reflecting IR!

"Terran Melconian" <terran@mit.edu> wrote in message
news:c3de8g$2tk$1@means.mit.edu...

In article <c3cgh0$ebo$1@otis.netspace.net.au>,
Joseph Goldburg <wizard1@SPAMnetspace.net.au> wrote:
Will IR bounce of all different cloured surfaces of a credit card?

I wouldn't be on it. Even if it works on your test cards, some
manufacturer somewhere is going to have used dyes that happen to be dark
at IR.

IR is suitable for detecting things like this only when you can use it
tranmissively (blocked by the card when present), not reflectively. If
you can't put the photodiode (or at least a mirror) on the *other* side
of the card, I think you'll be sorry trying to use IR.

I'd try ultrasonics or capacitative sensing.

 

[Paul Mathews]

Yes, at this short range, even 0.1% reflective surfaces are quite
detectable. Really, you need not worry about any kind of dyes have
low IR reflectance. Most things that have low reflectance in the
visible are at least somewhat more reflective with near IR. The
exception is carbon black, which is about equally non-reflective in
visible and near IR. Also, very shiny surfaces will pose sensing
problems at grazing angles of incidence. Again, you should be able to
sense most anything at a cm or less.
Paul Mathews


"Check It Out" <no@no.com> wrote in message news:<UOqdnYHZHdpAQcfdRVn-uw@centurytel.net>...

Isn't the sensing range to be 5-10 millimeters? I could detect a blackhole
at that range reflecting IR!

"Terran Melconian" <terran@mit.edu> wrote in message
news:c3de8g$2tk$1@means.mit.edu...
In article <c3cgh0$ebo$1@otis.netspace.net.au>,
Joseph Goldburg <wizard1@SPAMnetspace.net.au> wrote:
Will IR bounce of all different cloured surfaces of a credit card?

I wouldn't be on it. Even if it works on your test cards, some
manufacturer somewhere is going to have used dyes that happen to be dark
at IR.

IR is suitable for detecting things like this only when you can use it
tranmissively (blocked by the card when present), not reflectively. If
you can't put the photodiode (or at least a mirror) on the *other* side
of the card, I think you'll be sorry trying to use IR.

I'd try ultrasonics or capacitative sensing.

 

[Colubris]

"Check It Out" <no@no.com> wrote in message news:<UOqdnYHZHdpAQcfdRVn-uw@centurytel.net>...

Isn't the sensing range to be 5-10 millimeters? I could detect a blackhole
at that range reflecting IR!

snip

The problem then might be _not_ detecting whatever is across from the
sensor when no card is inserted. I suppose a hole or slot could be cut
across from the sensor so there is no reflective surface when the card
is not present.

Arch

 

[John Woodgate]

I read in sci.electronics.design that Paul Mathews
<optoeng@pioneernet.net> wrote (in <ed443a10.0403190710.588676f@posting.
google.com&gt about 'IR Prox detector with twiat', on Fri, 19 Mar 2004:

Most things that have low reflectance in the visible
are at least somewhat more reflective with near IR.

Some (black) vinyl records are transparent to IR (guess how I know -
think 'size detector'), and so is ebonite (EBONITE??).
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk