MS20 Information and Modifications

Tinhorn

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I spent half the day playing around with an MS20 PIR for those that are interested:    

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MS20 Current  Based on Voltage:

VOLTS   TRIPPED          IDLE
 6vdc     1.83 ma's       1.76 ma's
 9vdc     2.03 ma's       1.82 ma's
12vdc     2.25 ma's       1.90 ma's
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Warmup At Power On:

Is governed by C9 33uf) charging thru R12 (5.1K) apparently from R13 (1.5M)  Once this cap is charged to approx 2.8 volts, the warmup time period expires

This seems to be a sensitive part of the circuit and I could not remove the warmup time period.  I tried replacing C9 with a 1 and then 2 meg Resitor but MS20 would always stay triggered.

I then tried to "Charge" C9 with a 1K resitor connected to Batt (+) (6vdc) momentarily but no luck.   This apparently "overcharged" the cap, the volts started counting down (dropping) and when they reached about 2.7 or 2.8, the MS20 reset.

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Light Sensor Circuit Modification, adding Light Adjustment

Replace R27(6.8K) with 20K or 25K variable resistor (located near Auto/Test Switch)
Short out R24 (100K)(located near Auto/Test Switch)

To defeat Nite Time only Mode, could put a switch across the varialbe resistor.  The Light Sensor will be deactivated when the switch is closed.

NOTE:  The Light sensor is active only when the MS20 switch is set to "Auto".  This means the 1.5 "Retriggerable" time delay will be active and you should use a 2 sec time delay to prevent a possible Owl PF shutdown (exceding the PF's 3 min shutdown period discussed from time to time)

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Modification for using Q4 to trip Camera  (no relay or OptoIsolator required)

Note:  Swithes are not noted below, you will want a Power on/off switch and a switch on the Owl PF trigger wire that goes to D8 Cathode hole
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1st Determine which of the 2 wires from the OWL PF is most positive:

Connect Volt Meter across the 2 trigger wires, if it reads a negative volts, reverse leads, it should read aprox +3 volts, the RED lead is connected to "Positive" camera lead

2nd,  Remove these components from MS20:

Red, Black, and White Wires
Relay,  D1, R1, R2, R3, R22, light sensor,  C2,  D8, connected to Q4 Collector

3rd   Solder these things in:

Batt (+) lead to hole where D1 Cathode (banded end) was (don't forget switch)
           
2 wires to L3 hole where white wire was removed:  
1 goes to Batt(-) lead  
the 2nd goes to Owl PF's ground trip wire (not Postive trip wire)
           
Wire that leads to Camera's "Positive" trip lead (step 1) goes in Cathde of D8's hole   IMPORTANT:  this trace goes to Collector of Q4, nothing else should be connected to this trace (except Q4's Collector)  (don't forget switch)
                             
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Archilochus

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Hi Tinhorn,
Thanks! If I ever get around to tryin out an MS20, my work will be a LOT easier.
>>
On the warm up problem...."C9","R12", "R13", and all those other bits near the PIR element are important parts of the op-amp circuitry.  "C9" and "R12" are used to help filter out low frequency "noise".  "R13" sets the gain and is part of the high frequency "noise" filter.
My home-made sensors have the same warm-up problem. I just turn them on before I begin strapping them to the tree and by the time I'm done the sensor is usually ready to go.
>>>>>
I'd be wary of using Q4 to trip the shutter.  If ever something went wrong with Q4, you could potentially end up having the sensor battery voltage get shorted into the cameras circuitry. I don't know if the camera would croak with 6 volts applied, but I'm guessin it would not be happy.

Archilochus
 

Tinhorn

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Hi Archy

Thanx for the info on the filtering circuit,  I figured it was both filtering and (feed-back) Gain for that stage but wasn't sure.  I was hoping to use a Momentary Push Button to defeat the delay.  Like you said, I don't worry about it but some on the forum have complained about it from time to time.

It would always be safer to use OptoIsolaters for cam triggering but looking at the circuit,  It appears to me that the chances of full 6 volts getting to the cam would be mighty slim.  

There is a 100K connected to the base and the emitter is grounded,  the only thing connectd to the Collector is the Cam.  I supose if there was a Base/Coll short (but not to emitter) then some volts could go thru the 100K to the cam.  A blocking Diode on the Cam Positive Lead could be added insurance I guess, but I don't think the danger is all that great.

or am I missing something you spotted?

Thanx again

Tinhorn
 

Archilochus

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Hi Tinhorn,
Nope, I don't *think* there is ever likely to be a failure of the transistor, but for 70 cents (the cost of an opto-coupler) it's worth being *sure*

Archilochus
 

Richard Webb

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Tinhorn - I just returned from a family Boating/Camping trip, and found this much needed MS20 thread. Thanks. Out West during this time of the year with all the heat we need the night only option, but when I looked at the MS20 circuit board I had these thoughts: Why would the designer of that thing intentionally not put the right resistor on the board? He must have known that the correct resistor would make it work dusk to dawn like its competitors? The answer most likely is that the current has different paths to ground, and can easily bypass his light sensor. So, that's on hold for now. I still have 2 ea of the 7.62mm ammo cans, and plan to use your 6 volt MS20 idea with a lantern battery on both of them. The ammo can that I just completed went out at 9 volts with a bank of 6 ea "D" size batteries. I got the idea of using an ammo can with "D" size batteries from the Buckshot 35 (Real Tough Version).
 

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