Modifications for the MS-12 and MS-13 Occupancy Sensor/Motion Detector
Updated: 12/06/03
Removing Dusk / Dawn Sensing with Heat Shrink Tubing Defeating Dusk / Dawn Sensing Circuitry Add Dusk / Dawn Sensitivity Adjustment
Using the MS-12/13 as a Door/Window Sensor Adding 'Supervision' monitoring to the MS-12/13 Mod to Defeat the 6 minute IR timer
 
Heat Shrink Tubing trick | Defeating Dusk/Dawn | Adding Dusk/Dawn Adjustment
Mod for Door/Window Sensing | Mod for 'Supervision" Monitoring | Defeating the 6 minute IR Timer
WARNING:  Performing these modifications are done at your own risk.  I will not be held liable for any issues that arise from performing such modifications.

What's all this MS12/13 "Occupancy Sensor" Stuff?

    The MS12 and MS13 are quite sophisticated little devices. Not only are they a motion detector, they are also a dawn/dusk sensor too! The MS12 is the original occupancy sensor first developed by X-10 but after amazingly listening to the end-users (i.e.,... myself included!), they decided to implement a few user programmable features such as dusk/dawn Enable/Disable and user selectable delay (the delay in time the unit will send an OFF command once it is triggered by motion).  The passive IR motion detector sends a pre selected Unit ON command (via RF) when motion is detected and then an OFF command when no motion has been detected.  In the case of the MS12, this delay time is fixed at approximately 6 minutes.  This same delay time is user programmable in the case of the MS-13 (programmable in increments of minutes). The second sensor, the Dusk/Dawn sensor, sends an X-10 ON command (+1 unit code of pre selected house code for motion sensor) when darkness is detected and an OFF command when light is detected. As for the MS13s, the dusk sensor feature can be disabled such that the motion sensor send X-10 signals regardless of the state of the dusk/dawn sensor.  One weird thing which X-10 had originally decided to do (in MS-12 design only) was to integrate the two sensors such that the passive IR sensor only communicates (transmits RF) when the Dusk/Dawn sensor is detecting darkness. Hmmmmm........ If only there was a switch or control for this such that the two sensors can operate independently! Also, there should also be an adjustment for the Dusk/Dawn sensor.  X-10 amazingly listened to end users and promptly redesigned the MS-12 with useable enhancements, as in the case of the release of the newer, revised MS-13 Occupancy sensor.  The following modifications will work with both the MS-12 and MS-13 units.  The major difference between the two models in the incorporation of an additional Green LED and a reprogrammed PIC controller.

There are three ways to alter these dang Dusk/Dawn sensors. One modification is to completely remove the Dusk/Dawn sensor capability! There are two methods to accomplish this. The easiest and simplest way is to remove power to the Dusk/Dawn circuitry. Another variant to removing the Dusk/Dawn feature is to completely cover the CDS cell with heat shrink tubing by placing a long enough piece over the CDS cell which will fake the MS12 out in thinking that it is always dark. (Believe me, the snipping of the jumper is the easiest!!) The last modification is to add a Dusk/Dawn sensitivity adjustment. This required a small change to the circuit such that R8 (68K) is removed and a mini 150K (or so) ohm potentiometer is inserted in its place. This mod would allow for Dusk/Dawn sensitivity adjustment. This mod (granted not as easy as the previous) would require you to also make a small mod to the enclosure such that the potentiometer sticks out of the case (just a lil') so that you can simply adjust it with your finger. (Click on the picture above to view an enlargement of my modified MS12 with Dusk/Dawn sensitivity adjustment!)


Using Heat Shrink tubing to trick the MS12/13 Dusk/Dawn Sensor

Open the battery compartment and remove the two (2) AAA batteries. Remove the 4 screws on the back 4 corners and separate the top and bottom halves of the enclosure. Toward the center of the circuit board you will see 2 sensors. The motion sensor is the round "can-like" object in the middle of the circuit board with a square glass-like window. The Dusk/Dawn sensor is located just down and to the right of this (a glass bead with a squiggly line). Obtain a 1 inch piece of heat shrink tubing large enough in diameter to cover the CDS cell. Carefully heat the tubing until it fully shrinks around the sensor then quickly (while the tubing is still hot) pinch the top just above the actual CDS sensor with pliers. It is very important to seal the light out completely. Put it all back together and test to be sure it is operating properly.
 


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Defeating the Dusk/Dawn sensing circuitry

(You can refer to the MS-12/13 schematic for this modification)
Open the battery compartment and remove the two (2) AAA batteries. Remove the 4 screws on the back 4 corners and separate the top and bottom halves of the enclosure. Toward the center of the circuit board you will see 2 sensors. The motion sensor is the round "can-like" object in the middle of the circuit board with a square glass-like window. The Dusk/Dawn sensor (CDS1) is located just down and to the right of this (a 2-leaded glass bead with a squiggly line). Now, locate the wired jumper (D1, it is 3/8" long) just above the CDS1 sensor. To completely disable the MS-12A Dusk/Dawn sensor you must snip the jumper and be certain that the jumper is open. You can slightly bend one piece of it up so they will not touch. Put it all back together and test to be sure it is operating properly.

Believe it or not, but with this mod (totally eliminating CDS1 dusk/dawn circuitry), I have noticed an increase in motion detection range. I'm also predicting a little longer battery life too!  Actually, removal of the CDS cell (by snipping off completely) and resistor R14 (100K) will completely disable the dusk/dawn circuitry,... where as it will not draw any unnecessary current.

Without either of these two mods, you would have to code/program each MS12 such that they are separated by two unit codes (due to the fact that the Dusk/Dawn sensor uses the +1 unit code of motion sensor). Now, when the Dusk/Dawn sensor is disabled, you can then code them closer together, not worrying about the "+1 unit code" problems!
 


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Adding a Dusk/Dawn Sensitivity Adjustment

(You can refer to the MS-12/13 schematic for this modification)
Open the battery compartment and remove the two (2) AAA batteries. Remove the 4 screws on the back 4 corners and separate the top and bottom halves of the enclosure. Toward the center of the circuit board you will see 2 sensors. The motion sensor is the round "can-like" object in the middle of the circuit board with a square glass-like window. The Dusk/Dawn sensor (CDS1) is located just down and to the right of this (a glass bead with a squiggly line). Now, to the far right of the CDS1 sensor, locate resistor R8 (68K) and carefully remove it from the circuit board. Obtain a mini 150K potentiometer and solder it in its place. (you might have to bend the potentiometer's leads a bit to make it fit). The enclosure (top and bottom shells) will have to be customized (exacto-blade or Dremel) to allow for the potentiometer body and dial. Make sure that the potentiometer daily extends past the body of the enclosure such that you can easily adjust it with your finger. Set the potentiometer to its middle position (roughly 75K) and test to be sure it is operating properly. If all works fine, reassemble and try fooling around with the adjustment to fit your need.
 


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Modifying the MS-12 to be a Door/Window Sensor

(You can refer to the MS-12/13 schematic for this modification)

Open the battery compartment and remove the two (2) AAA batteries. Remove the 4 screws on the back 4 corners and separate the top and bottom halves of the enclosure.

There are many variants to adding a reed switch to the MS-12A. The first is to connect the reed switch such that when the reed switch is open (magnet not nearby), the MS-12A will transmit an X-10 ON signal, and will send an X-10 OFF when the reed switch is closed (magnet nearby). Another variant would be just the opposite, X-10 OFF when closed, X-10 ON when open. There are also other variants where you can have both the Dusk/Dawn and IR motion sensors operate totally independently. There is also another variant which would allow you to either totally eliminate either the Dawn/Dusk or IR motion sensor capabilities. I'll try to focus on all these variants separately.  And finally, I received a few emails regarding other methods of modifying the occupancy sensors and decided to include them here also.  Although some of these mods have not yet been verified by myself, I still figured I'd include them here in case others wanted to attempt them.


MOD FOR X-10 OFF WHEN REED SWITCH IS OPENED, X-10 ON WHEN CLOSED!
The first step is to locate the Jumper (D1) which will be snipped. After cutting the jumper with snippers, be certain that the two separate halves of the jumper are separated, not touching each other or anything. The next step is to add a new 10K resistor and reed switch. This new 10K ohm resistor is soldered to left half of remaining jumper The Magnetic Reed Switch leads are then soldered to the MS-12A (one to other side of resistor, the other to GND) You must then notch a small slot on the lower half of the enclosure to allow for the reed switch wire to exit. Put it all back together and test to be sure it is operating properly.

Your completed/modified MS-12A / Door/Window RF Sensor should resemble this picture.


MOD FOR X-10 ON WHEN REED SWITCH IS OPENED, X-10 OFF WHEN CLOSED!
The first step is to locate the Jumper (D1) which will be snipped. After cutting the jumper with snippers, be certain that the two separate halves of the jumper are separated, not touching each other or anything. The next step is to add a new 10K resistor, a new 1Meg resistor and a reed switch. The two resistor are tied together in series and connect across the left side of the snipped D1 jumper and GND. One side of the reed switch is then connected to the junction of these two resistors and the other side connected to +3V.
(TO BE CONTINUED SOON!)


MOD FOR INDEPENDENT OPERATION OF DUSK/DAWN AND IR MOTION SENSORS
The first step is to locate the Jumper (D1) which will be snipped. After cutting the jumper with snippers, be certain that the two separate halves of the jumper are separated, not touching each other or anything.
(TO BE CONTINUED SOON!)


ANOTHER SIMPLE MOD TO CONVERT UNITS TO DOOR/WINDOWS SENSORS

I have received a few emails describing another simple method to convert these units into door/window sensors, similar to the mod functionality described above.  Although I have not actually tested this mod, I figured I'd still include it and maybe when some one out there reads this and successfully attempts this mod, they can inform me of such.

This alternative method is quick and simple.  You can simple cut off the CDS cell (leaving long leads, snipping leads toward the top of the CDS cell) and then, across these two now-separate leads, solder the contacts from the reed switch (or any other contact closure switch).  This mod simple replaced the CDS (cadmium sulfide) photo-resistive cell with a simple contact closure.  Below is a copy of one of those email, just in case you wanted to contact the author.

Hello Tom!

Just finished reading the modification for X10 ON when switch open and X10 OFF when switch closed. This is more easily
implemented by replacing the CDS1 sensor with the reed switch and a 1K resistor in series. When the switch is closed,
simulates a DAWN condition. When the switch is open, simulates a DUSK condition.

Jean-Claude Chagnon
Domotique-Residentiel.Com

Thanks for everyone's comments and suggestions.
(TO BE CONTINUED SOON!)
 


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Adding a 'Supervision' feature to the Door/Window Mod.

(You can refer to the MS-12A schematic for this modification)

(TO BE CONTINUED SOON!)
 


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Modification to Defeat the 6 minute IR timer

(Thank goodness for the MS-13s as they now have a user-settable timeouts!)

(You can refer to the MS-12A schematic for this modification)

NOTE:

Unfortunately, there seems to not be an easy solution.  The 6 minute timer is actually a function managed internally by the PIC code; no components will alter the delay (dangit!).  There are ways though to "swap" sensors such that the IR Motion sensor could drive the MS-12a PIC's Dusk/Dawn input.  This input does not have an associated "lockout" time delay as is the case with the PIC's Motion sensor input.  Hmmm.. you'd think that swapping sensors would then work!  Well, I have tried this (I believe someone else did something similar) but had problems with delays in RF triggering.  I have noticed that there could be up to around a 9 second delay between the time the motion sensor detected
motion and the time the MS-12a transmits RF.  Weird!??!?!?!?  Haven't figured this one out yet.  The PICs input (originally designed for the dusk/dawn sensor) seems to inherent a "scan" period for sensor measurement.  Still working though.... as time permits!  You can be sure that I'll post to the newsgroup if I make any progress

(TO BE CONTINUED SOON!)
 


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