series, so current will flow and all LEDs will light green
only when all doors are locked.
The garage door is a special case. I want it to show
orange (red and green) when all doors except the garage
door are locked. Figure 4 shows how placing resistor R2
across the garage door switch makes this happen.
The switch is not shown because it is open. Since all
other doors are locked and R2 provides a current path
around the garage door switch, there is current flow
through LED3 in both directions. Positive current is shown
as red, negative current as green, and current in both
directions as black. In this case, all of the locked doors will
show a dim green rather than the usual bright green. The
low voltage and high impedance of the power supply
make the circuit safe for any kind of fault.
You can make the diode logic circuit for each door on
a 0.78 x 1 inch perforated prototype board. The front and
back side of the board are shown in Figure
5. The Molex connectors for the switch
(SW) and the input/output (I/O) add a little
cost, but make assembly at the door frames
Running the wires is the most time-consuming part of this project as
mentioned. You can hide the wires under
the casing down to the floor and then
through the floor to an unfinished
basement space. If that is not available, you
24 June 2017
QTY PART DESCRIPTION
1 2191453 Proto Board 3. 15 x 3.94 6.95 6.95
12 36311 IN914 Diode 0.05 0.60
8 233437 Molex 0.1” Two-pin Right Angle Header 0.19 1.52
8 234704 Molex 0.1” Housing 0.09 0.72
20 234923 Crimp Terminal 0.07 1.40
3 2187892 Micro Switch 0.65 1.95
1 617545 Magnetic Proximity Switch 7. 19 7. 19
4 2186460 Red/Green LED 0.15 0.60
2 173164 #24 Twisted Pair Wire 00’ 9.95 19.90
1 2082142 18V AC Wall Adapter (optional) 4.95 4.95
TOTAL $45.78 TOOLS
1” hole saw
Long 3/8” drill bit
Solder and soldering station, wire cutters, etc.
Terminal crimper (not essential but highly recommended; Jameco 227491, $16)
Machine tool lathe (helpful to make the PVC LED module assembly)
■ FIGURE 4. The garage door circuit adds a
resistor to indicate safe exit (orange)
through the last unlocked door.
■ FIGURE 5. The front (left) and back (right) of the prototype
board door module. Diodes D1, D2, and D3 can be seen on the
front of the board.
■ FIGURE 3. The components that are active during the
negative half cycle.