Step 1: Tools and Materials
(x1) 9V Relay (Radioshack Catalog #: 275-005)
(xvar) jumper wires (Radioshack Catalog #: 276-102)
(x2) Heavy duty 9V battery clips (Radioshack Catalog #: 270-324)
(x2) 9V batteries (Radioshack Catalog #: 23-866)
(x1) Prototyping PCB (Radioshack Catalog #: 276-170)
(x1) Piezo Buzzer (Radioshack Catalog #: 273-080)
(x1) 5K Ohm Potentiometer (Radioshack Catalog #: 271-1714)
(x1) Potentiometer cap (Radioshack Catalog #: 274-415)
(x1) 470 Ohm Resistor (Radioshack Catalog #: 271-1317)
(x1) 3" diameter acrylic tube
(x1) Magnet (Radioshack Catalog #: 64-1888)
(xvar) lamp-pull ball-chain
Hot Glue Gun
I used a laser cutter to make my own personal enclosure, but one could easily modify a pre-made project enclosure to suit the needs of this project.
Step 2: Modify the 9V Relay
I trimmed all of the leads off of the relay except the ones that attach to both ends of the coil. I then soldered wires from each of the leads from the coil.
The purpose of the magnet coil in this circuit is to detect when the hanging magnet from the cylinder passes over it. The magnet sways when the earth moves, triggering the piezo buzzer to sound, and the LED to illuminate.
Step 3: Create a Home for the 9V Relay.
Using CorelDraw, I generated a series of files for the enclosure, and then used .3" thick acrylic sheets to make the housing.
The file has 6 sides, with holes for the piezo buzzer, LED, and the acrylic tube. It is attached to this step of the instructable.
After I had my laser-cut parts, I glued my relay into it's home in the round, that will later be inserted into the tube.
I placed the relay into it's nook, then hot-glued it into place. After it was in place, I soldered a wire from each of the leads.
Step 4: The Circuit
Step 5: Connecting Two Batteries to the PCB
I designated one ground rail, one 9v + rail, and another 9V - rail. I soldered the red positive wire from one battery clip to the top rail of the PCB, and took the black negative wire of the same clip and soldered it to the lower part of column 47. I soldered the other battery clip in by connecting the red positive wire next to the negative wire of the other clip, and the black wire to the clip of the bottom rail.
Step 6: Solder the 741 Op Amps
Step 7: Pin 4 and 7
Step 8: Pin 6 to Pin 3, and Pin 3 to GND
This is essentially reading the shifting output of the magnetic coil inside the relay, and comparing it to a normalized value.
Pin 3 on the left opAmp IC gets connected to the grounded rail that was established in column 47 of the PCB.
Step 9: Solder the Relay .
Step 10: Potentiometer
Step 11: Wire Buzzer and LED
I ran a 470 Ohm resistor from the 9V+ rail, and connected that resistor to the positive lead of the LED. Both the LED and Piezo buzzer's negative lead run to the output pin (6) of the right IC.
Step 12: Assemble the Enclosure & Sink the Magnet to the Relay Coil Into the Tube.
I punched a small hole in the lid of the acrylic tube with a nail, and then ran the lamp chain with a magnet hot-glued to it so that the magnet just hovered over the relay coil. You want to hang the magnet so that it almost touches, you can see that it wants to stick to the relay, but it doesn't actually magnetize to the component.