Homebrew PCBs

Hi Robert,

Thanks for pointing out that the unit has the internal Schmitt trigger which
some people might have missed.  

 

Similar result can be achieved with a plain opto-interrupter though since a
proper design should use a well-defined trigger voltage which normally would
be an external comparator with or without added hysteresis.

 

The tested unit is not sensitive to supply voltage though.  Yes, it should
be used with a regulated supply for best performance but that is so common
today.   For example, connecting it to a regulated 12V supply commonly
available in a PC, the trip point only changes 4 microns for a drastic
supply change of + or - 1V.  A typical 0.2V change would be less than 1
micron trip point change. (1 micron=39 micro Inches)

Bertho

 

From: listgroups08@...    Sent: Thursday, April 03, 2008 22:37
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 



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