switch and I/O connectors into the space
behind the sheetrock, they can be plugged
into the circuit board, and the PVC module
can be pressed into the sheetrock hole.
Figure 9 shows how to install a switch for a dead bolt
lock. A switch like that in Figure 8 is mounted in a slot in
a 1” section of 7/8” wood dowel. The dead bolt hole is
then extended about an inch with a 1” hole saw or auger
bit, and then drilled all the way through with a 3/8” bit.
The mounted switch goes into the dead bolt hole with the
connector and wires passing through the 3/8” hole to
connect to the circuit board module in Figure
5. The face of the dowel stops the dead bolt
from traveling too far and smashing the
Figure 10 shows how to attach a
magnetic proximity switch for a garage door.
If your home has multiple garage doors,
connect the door switches in series to a
single circuit module located at a convenient
inside location. Additional switches for
windows can be added in series to any circuit
module to make the LED indicate the security
status of a zone with multiple entry points.
Patio switches are a challenge because
the typical latch moves out, down to engage
the door, and then back to pull the door
tight. Here, I extended the switch lever arm
so that the downward motion of the latch
pushes the switch as in Figure 11.
If you want an additional House-Secure
indicator in an upstairs bedroom, for
example, just add to the series loop an
additional green LED in parallel with a
reverse-facing diode without the extra diodes and switch.
This indicator will show green when all doors are locked.
Parts for a Four Door
The Parts List shown
here is for a four door
system (stock numbers are
from Jameco Electronics;
home is different, so you
need to adjust this list for your particular design. Various
components for this project including assembled printed
circuit boards (refer to Figure A) can be purchased from
the Nuts & Volts webstore ( store.nutsvolts.com).
Taking It to the Next
If you are an inspired DIY enthusiast, you can — with
the addition of separate red and green LEDs and one extra
resistor in each door circuit — build a base station that can
indicate which doors are unlocked. The resistors go in
series with the red LEDs in a binary sequence; for
example, 10, 20, 40, 80, 160 ohms in a five door system.
This makes the positive voltage Vp developed across the
series string a unique function of the 32 possible
combinations of locked and unlocked doors.
With appropriate offset and gain adjustments to Vp,
26 June 2017
■ FIGURE 10. A magnetic proximity switch installed
on a garage door. The steel on the right side is the
garage door track. The brighter white box holds the
magnet, and is attached to the edge of the door and
moves vertically with the door. The white box with
the two wires coming out the bottom is the magnetic
switch. Its contacts close when the two boxes are
within about 3/4” of each other.
■ FIGURE 9. A switch ready for
mounting in a deadbolt hole
■ FIGURE 11. A patio door lock switch.
■ FIGURE A.