Magnetometer

The circuit described in this article is incredibly sensitive to changes in the magnetic field. It can be used to detect earthquakes, but it can also function as a car alarm or for theft prevention. The construction is straightforward and only standard components have been used in the design.

Resistors
R1 = 470kΩ
R2 = 330kΩ
R3 = 220kΩ
R4,R10,R13 = 47kΩ
R5,R6,R7,R9,R11 = 100kΩ
R8 = 10Ω
R12 = 10kΩ
P1 = 1MΩ preset
P2 = 10kΩ preset
P3,P4 = 100kΩ multiturn preset
Capacitors
C1 = 10µF 16V radial
C2 = 1µF 16V radial
C3,C4,C5,C9,C12 = 470nF
C6,C7,C10,C13,C14,C15 = 100µF 16V radial
C8,C11,C16,C17 = 100nF
Semicondcutors
D1-D4,D6-D10 = LED, red, 3mm
D5 = LED, green, 3mm
D11 = 1N4148
IC1 = LM380N-8
IC2 = 4069UB (unbuffered version)
IC3 = TL072CN
IC4 = LM3914N
IC5 = 78L12
Miscellaneous
S1 = pushbutton, 1 make contact
L1 = coil, e.g. discarded mains transformer 230 V / 12 V @2A
PCB, ref. 050276-1 from www.thepcbshop.com