How should I combine these sensor outputs?

[Kasterborus]

If I had an array of these sensors - each one reading the light from a
single scanning laser beam (ie only one sensor is ever illuminated at
a given moment)

http://www.taosinc.com/images/product/document/TSL12S-e23.pdf

Can I just tie all the output lines together, or is there a more
correct way?

On a scope trace I've noticed that each sensor works well when used
alone, but when I combine the outputs the reliability seems to
decrease.

Dave

 

[John Popelish]

If I had an array of these sensors - each one reading the light from a
single scanning laser beam (ie only one sensor is ever illuminated at
a given moment)

http://www.taosinc.com/images/product/document/TSL12S-e23.pdf

Can I just tie all the output lines together, or is there a more
correct way?

On a scope trace I've noticed that each sensor works well when used
alone, but when I combine the outputs the reliability seems to
decrease.

You should not connect these outputs directly together,
because each is trying to produce its specific voltage,
regardless of the load connected. Unfortunately, each is a
bit better at producing a low voltage output than a high
(light signal) output, so if only one is illuminated at a
time, the dark one wins that tug of war. Connect them
through a pair of series resistors, say, 10k ohms, each.

This will average the two outputs, accurately, though since
only one is illuminated at a time, the result will still be
lower than either alone.

A less accurate way to get a signal that is the larger of
the two is to connect them together through a pair of
Schottky signal diodes, anodes to the outputs cathodes tied
together. This will lose the forward drop of a diode, but
output the most positive signal from the pair at all times.

 

[Kasterborus]

Thanks for the repl John,

One question - when you say a pair of series resistors, do you mean
one for each of the (2) sensors? If I were to use 10 sensors, would I
put one 10K resistor in series with each output line?

I thought there was probably a better way.

Like this - (copy to NP to view)

o----o----o----o----o---o----o----o---o----o-----------
o----o----o----o----o---o----o---oo---o----o-----------
| | | | | | | | | |
/ \ / \ / \ / \ / \ / \ / \ / \ / \ / \
(_/_)(_/_)(_/_)(_/_)(_/_(_/_)(_/_)(_/_(_/_)(_/_)
\_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/
| | | | | | | | | |
| | | | | | | | | |
.-. .-. .-. .-. .-. .-. .-. .-. .-. .-.
| | | | | | | | | | | | | | | | | | | | -
| | | | | | | | | | | | | | | | | | | |
'-' '-' '-' '-' '-' '-' '-' '-' '-' '-'
| | | | | | | | | |
o----o----o----o----o---o----o----o---o----o----------

 

[John Popelish]

Thanks for the repl John,

One question - when you say a pair of series resistors, do you mean
one for each of the (2) sensors? If I were to use 10 sensors, would I
put one 10K resistor in series with each output line?

I thought there was probably a better way.

Like this - (copy to NP to view)

o----o----o----o----o---o----o----o---o----o-----------
o----o----o----o----o---o----o---oo---o----o-----------
| | | | | | | | | |
/ \ / \ / \ / \ / \ / \ / \ / \ / \ / \
(_/_)(_/_)(_/_)(_/_)(_/_(_/_)(_/_)(_/_(_/_)(_/_)
\_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/
| | | | | | | | | |
| | | | | | | | | |
.-. .-. .-. .-. .-. .-. .-. .-. .-. .-.
| | | | | | | | | | | | | | | | | | | | -
| | | | | | | | | | | | | | | | | | | |
'-' '-' '-' '-' '-' '-' '-' '-' '-' '-'
| | | | | | | | | |
o----o----o----o----o---o----o----o---o----o----------

I am not sure of your symbology, but if this diagram shows
10 amplifiers with their outputs pointing down, and a common
output rail across the bottom of 10 output resistors, then,
yes, that is exactly what I am talking about.

There are other ways that involve using a separate opamp as
the summer of all those output currents, but I have no idea
what this signal goes to, so I can't say if that method
would be better than this one.

 

[Kasterborus]

John

Yes, you understand my (quickly drawn) diagram.

Thanks for helping me out - I tried what you suggested last night and
it works beautifully. My "laser harp" now has a reflective range of
about 5' - which is perfect.

Info: http://en.wikipedia.org/wiki/Laser_harp

Thanks again!

 

[John Popelish]

John

Yes, you understand my (quickly drawn) diagram.

Thanks for helping me out - I tried what you suggested last night and
it works beautifully. My "laser harp" now has a reflective range of
about 5' - which is perfect.

Info: http://en.wikipedia.org/wiki/Laser_harp

Thanks again!

We usually draw diagrams with signals passing left to right,
with voltage supplies placed positive across the top,
negative across the bottom. But since you are thinking harp
thoughts, your way makes more sense. ;-)
Congratulations.

 

[Rich Grise]

We usually draw diagrams with signals passing left to right,
with voltage supplies placed positive across the top,
negative across the bottom. But since you are thinking harp
thoughts, your way makes more sense. ;-)
Congratulations.

Some people write software:

Cheers!
Rich