Next Modification

kmitch

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I think it was Tinhorn who had created a schematic of the MS20 PIR and identified R13 as the component which controlls the detection sensitivity. I played with this a little over the weekend and it seems to work. In the camera I am building I will install a pot to adjust the detection range. I think this is probably a worthwhile addition since detection range will vary with the ambient temperature, cold weather extends the range.

Perhaps the next addition to the camera design should be automatic switching of the PIR range for day versus night photos. The range would be reduced at night to the flash range.  

I think this would go a long way toward no photos without game. Has anyone looked at this?

Keith
 

Tinhorn

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Good Work kmitch,

I never did do any experimenting on the sensitivity adjustment and am looking forward to seeing what you discover, especially since summer time heat is right around the corner.  I'm wondering how touchy the resistance is to make the sensitivity change....

Speaking of summer time heat, I'm still in need of the 3 month hibernation pill, if anybody has any extra's........

Tinhorn
 

Archilochus

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Hi KM,
Changing R13 will change the gain - but be careful!  The op-amp, R13, and C10 not only amplify the PIR element signal, they also form part of the circuits "passband" filter - or the frequency of signals that will be considered "good" and amplified.  The typical PIR motion sensor amplifies signals somewhere between ~0.5 to 10 cycles per second, and rejects signals outside this "passband".  This helps eliminate a lot of bad triggers from various sources of interference - the sun, radio, etc.  Changing R13 too much could cause an increase in false triggerings.  Also, any wires you attach to run out to your sensitivity adjuster are going to act like little antennas, and might add further to falsing problems.

If you like doing sums.... try this....

Cutoff Frequency = 1 / ((2Pi)xRxC)
Freq in cycles/sec (Hz), R in Mohms, C in uF

Let us know about your results - sounds like an interesting project!
Archilochus

PS - a really easy "no electronics" method of adjusting sensitivity is to just add layers of material over (or behind) the lens - something like Fresnel Techs PolyIR 2 material - keep adding layers until you have the range you want.  Other materials can be used too - test 'em out to find ones that work!
 

kmitch

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Arch,

I agree that changing R13 will change the bandwidth. In my primative walk test it did not seem to affect the function. I could turn the gain up far enough to cause the PIR to never reset. Any suggestions on where else the gain can be modified electronically? Another good effort would be to see if the bandwidth could be modified to filter out really fast events like birds.  

In one of my cameras I glued the fresnel lens to the inside of the case and mounted the MS20 board on some 1-1/2" machine screws behind the lens. The distance between the lens and PIR can be adjusted to change the sensitivity. This camera produces more good pictures the my other one which uses the MS20 in it's original housing. This convinced me that the path to no lanscape photos without game is to tune the PIR sensitivity to match the camera range.

Keith
 

gantley

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Comment about Day Only mode....

We take out R22 which is the LDR.  This LDR seems to be low resistance in light.  During daylight, R22 allows enough voltage to feed thru to the base of Q3.  Just so happens that Q3 turns off the 3rd stange of the op amp to keep from trigering the 4th stage of the op amp which drives the transister that turns on the relay....

So, if you replaced R22 with a LDR that has high resistance in light, then we have day mode only.  

But is there a LDR that is high resistance in light?  
 


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