Discussion in 'The Projects Forum' started by Chris-S, Oct 26, 2013.

1. ### Chris-S Thread Starter New Member

Oct 26, 2013
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0
Hi all, firstly my electronic skills are medium and my circuit design skills are almost none.
I have an arduino project to detect 100 light sensors, so my first thought was to use the resistance or voltage checking facility..

But the help I need is about the chained circuit, something like: If each activated LDR in the line bypasses a 100k resister, i could simply measure the total resistance to find out how many sensors are activated (or not activated, i don't mind calculating it backwards)

Here is about as far as i got with my circuit, no idea if i need the 1m ohm resister to make it complete.. can someone help me with this design?
Many thanks!

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2. ### ErnieM AAC Fanatic!

Apr 24, 2011
7,906
1,789
With 100K resistors and 100 sensors your off resistance is 10 Mega ohms. That's so near an open circuit you may want to rethink the overall scheme. Breaking the chain into several smaller chains would help.

You say "activated (or not activated)" like it is a digital state. There's a lot of gray area as it goes between full light and full dark. If that covers several sensors your results get skewed.

Your statement about each "LDR in the line bypasses a 100k resister" makes sense. Your schematic does not make sense.

3. ### MrChips Moderator

Oct 2, 2009
14,264
4,183
One technique for measuring the resistance of 100 LDRs would be to wire them in an 10 x 10 matrix and interrogate each by scanning in the same manner that one would scan keyboard switches.

4. ### John P AAC Fanatic!

Oct 14, 2008
1,671
241
What exactly does "detect 100 light sensors" mean?

Detect that any one is seeing light?
Detect that any one is not seeing light?
Detect how much light is falling on the most brightly illuminated one?
Measure the light on each one individually?
(many other options)