HOME
A
BC
D
Antenna
12V DC
From intercom
E
Fig. A: Wires behind the apartment intercom control
panel. Fig. B: The terminal screw posts (shown in
yellow circles) with my 2-conductor cable (copper/tin)
connected to the door button contacts.
F
Fig. C: Panel replaced with the wire hanging down.
Fig. D: Holes for power and door-signal wires drilled in
the project box. Fig. E: Connected relay board in the project box. Fig. F: Relay connections and wireless key fob.
OK, time for kit and intercom to meet. The RF
relay kit consists of a small printed circuit board
that I decided to enclose in a project box. Following
the board’s layout, I drilled holes for the antenna in
one end of the box and for the power and Door wires
in the opposite end (Figure D). I put the board inside
and connected the Door wires to one of the 2 relays’
Normally Open and Common terminals.
I connected the power supply to the relay
board’s power terminals (Figure E) and performed
the learning procedure for the remote, per the
included instructions. Finally, I mounted the box
on the wall with adhesive tape, with the antenna
wire hanging down.
My apartment is on the 2nd floor directly above
my building’s entry, so range on the transmitter
fob (Figure F) is not an issue. I can activate the relay
from my bedroom or from in front of the building.
After some experimentation, I found that the
remote also works from across the street (about
100' away) and from various places on the 6th floor.
It also works from other points behind 4–5 thick,
prewar walls or floors, so it seems likely to work from
any apartment in the building. And it’s a rolling code
transmitter, so no, not just anyone with a remote can
activate the relay.
And there you go: a keyless entry. I might caution
that you not try this at home unless you’re very
snuggly with your landlord. It’s not the most impressive hack, and I want to find a good way to hide the
receiver and wire, but it sure makes my life easier.
So, what does the second relay button do?
Nothing. At least, not yet.
Ryan O’Horo is 24 years old and lives in Queens, N. Y. He’s
a web developer professionally, and he also co-founded
Make:N YC. Visit his project blog at cravediy.com.
Find Your Center
Often enough, I find I want to cut a piece of
reasonably uniform wood or other material
roughly in half.
Instead of measuring, I use that little trick
I learned as a school kid. Just balance it on two
fingers and bring your hands together until your fingers
touch and the piece balances. It’s a quick and easy way
to find approximate center. —Frank Joy
Find more tools-n-tips at makezine.com/tnt.
Photography by Ryan O’Horo
148 Make: Volume 15
