Homebrew PCBs

Hi Bertho and Mark,
                                I had a look at the web page you mentioned.

I just though I would mention that the opto couple mentioned is not at all 
like the common garden variety.

A common opto couple has a light emitting diode and a photo transistor. The 
one mentioned has an active circuit (schmitt trigger) incorporated with the 
sensor and hence the extra connection.

Normal opto couples have four connections, diode Anode(A), diode Cathode(K), 
transistor Emitter(e) and transistor Collector(c). The one you mentioned has 
an extra connection to supply voltage to additional circuitry for the 
hysteresis trigger.

The performance of the one mentioned is excellent especially considering 
that it is working with a 1/4mm aperture.

I just thought I would mention this so others know that while this unit is 
excellent, extra design considerations must be made to give it a well 
regulated voltage supply. It is not a drop in replacement for the garden 
variety.

However the garden variety have apertures from 1/2mm to 1/10mm, with the 
1/2mm being the most common. It would be interesting to see the specs for 
the 1/10mm units.

Thanks, Robert.

----- Original Message ----- 
From: "Bertho Boman"

Hi Mark

Keep up your excellent work!

This is a very interesting application!  In addition to Robert's comments on
the opto interrupter accuracy here is a link to an accuracy evaluation of
them:

http://www.vinland.com/Opto-Interrupter.html

<snip>

Bertho


From Mark Lerman   Sent: Wednesday, April 02, 2008 19:32
----<snip
I used a precision optical sensor to find the leading edge of the
board as it enters the printer. I wonder if I can make double sided
boards with adequate registration? For now I think I'll stick with
what I have. A double sided board can easily be made using thinner
board and gluing two boards together using registration holes and pins.
Mark