[E-Star]
You will need:
1) A cellphone [contracted or prepaid, your choice]
2) A wired, earbud-style handsfree headset for the cellphone
3) A 12VDC car charger for the cellphone
4) A printed circuit board [Radioshack Catalog #: 276-150]
5) A 741-style operational amplifier chip [Radioshack Catalog #: 276-007]
6) 12VDC Miniature Relay [Radioshack Catalog #: 275-233]
7) One (1) 100k ohm 1/4 watt resistor
8) One (1) 1k ohm 1/4 watt resistor
9) Several feet of thin gauge hookup wire
10) Soldering iron and Rosin core solder
11) A Multi-meter
12) A small plastic project box
STEP 1: BUILD THE AMPLIFIER CIRCUIT
This is by far the most difficult step. If you are not able to complete
this step, this project may not be for you. All it really requires is a
little bit of patience, and some basic soldering ability.
Complete the circuit as shown on the diagram. This circuit will be built
on the printed circuit board. Start your build on one end or the other so
that there will be room for adding the relay to the board.
STEP 2: ADD THE RELAY CIRCUIT
Next, we add the relay to some of the spare room on the PC board. New
connections on the diagram are shown in gray.
STEP 3: INTERFACING WITH THE CELLPHONE
Cut and strip the wires of the headset as close as possible to one of the
earbuds. If you have a mono headset, this should be easy as there is only
one choice! Use your multimeter to find which of the two wires leading to
the earbud is (+), and which is (-). You can do this by plugging the
handset in to the cellphone and checking for voltage readings as you press
keys, etc, which causes a sound signal (voltage) to be sent to the earbud
lines. If you exposed a single wire (+) surrounded by an insulating line
(-) when you cut the headset, you don't need to plug it in and test to
know the difference. Unplug the headset again and splice the (+) headset
wire you just exposed to the (+input) wire on the printed circuit. Splice
the (-) wire to the (-input) wire.
STEP 4: SPLICING THE CIRCUIT INTO YOUR ELEMENT
Carefully connect the (+power) wire on the printed circuit to a source of
constant 12V power. Connect the (-ground) wire to ground. Splice the
(-actuator) wire to the door unlock wire. This wire is located above the
left kickpanel on the driver's side, under the dash. This wire is white
with a green stripe.
STEP 5: TEST AND MOUNT
At this point, you can plug the cellphone into the headset and call the
phone. This should cause the ringtone, otherwise heard through the
earbud, to cause the amplifier to send a much higher voltage through the
relay, thereby causing the unlock wire to connect with ground and thus
unlock the door. If you have issues here, check all of your connections.
It also doesn't hurt to have your cell headset volume at maximum and a
loud but simple ringtone selected. (I use a single DING text message
tone)... If all is well, mount the bare circuit neatly into the plastic
project box and use double-sided tape to secure it under the dash or on
the firewall. Plug your phone charger in to an auxiliary outlet (that's
only on when the key is on) or go ahead and carefully disassemble (smash)
the 12VDC plug on your phone charger and wire the charger in directly.
Secure the phone under the dash or against the firewall. (I use velcro to
attach it under the dash. If you keep the phone in an area away from the
firewall or body, it will have less signal blocked by steel and get better
reception.)
IF YOU MADE IT THIS FAR... ENJOY YOUR E-STAR!
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