Enclosing the PIR modules
I purchased 4 PIR modules
to use as warning devices checking for predators
around the chicken coop. But that is outside and
the modules have no enclosure.
Then came Easter and I got a basket of candy in
The PIR modules are 1.26 inches by < 1 inch (32mm X 24mm).
(Someday the whole world will use inches and feet.)
The medium plastic eggs are about 60mm long by 42mm diameter.
Those of you good at math will realize the egg diameter is
slightly less than the diagonal of the module
but this doesn’t matter. It works.
The diameter of the sensor dome is about .98″ (a little over 24mm).
The first step is to cut a circle out of the fat (short) end of
the egg exactly that diameter. I tried a number of ways of cutting.
The best way is spinning it on some support through the small hole
and using a small cutting tool to trim out the circle.
Now comes the tricky part.
The egg end is too deep for the sensor to fit and it is going to be
outside so needs to be water tight.
So I measure the depth of the circuit board and the sensor base
(I only had inch tools)
it is about .178 inches (4.5mm) and we want the module to sit inside
the egg end my a bit so I add .115 inches (2.9mm appx.) for a total
of .293 in or 7.44mm.
Then I measure the total depth of the cut egg end.
It looks like about .87 in or 22mm.
Subtract the .293 from the .87 leaves us .577 in or 14.6mm
This need not be exact but take 1/2 of what is left and make a cut
that far from the top.
So about .288 in or 7.3mm down from the first cut we make another cut.
This small piece will want to break but the eggs are very inexpensive.
this cut looks good so now I invert the cut piece and insert the
sensor to check the fit.
It fits well now for some glue and time.
Remove the sensor and invert the two pieces. Some tape around the
junction will keep the cement from flowing out. fill the circular
V shaped junction between the pieces with something.
I use solvent cement. I suppose RTV would work but I have had
RTV leak and don’t trust it.
When dry I spray painted mine flat black and cut a rectangular hole
in the back for the cord. inserted the cord and sealed the opening.
The sensor should be sealed where the dome meets the housing.