An electromagnetic field (EMF) meter or gaussmeter measures the relative strength of magnetic fields. EMF meters can be used for a number of reasons from testing the strength of electromagnets to checking for magnetic fields around unshielded electronics to searching for magnetic field disturbances when ghost hunting. If you want to build an EMF meter, you can purchase all the necessary parts at your local hardware store and should have it assembled and testing magnetic fields in less than an hour.
Connect the 5-volt voltage regulator to pins 1, 2, and 3 on the upper left hand side of the breadboard's power bus.
Attach the red 9-volt battery connector wire to pin 1 on the 5-volt voltage regulator.
Connect the black 9-volt battery connector wire to pin 2 on the 5-volt voltage regulator.
Set the Hall Effect device into the upper right hand side of the breadboard's power bus in line with the 5-volt voltage regulator.
Connect a green wire from pin 3 on the 5-volt voltage regulator to pin 1 of the Hall Device.
Connect a black wire from pin 2 on the 5-volt voltage regulator to pin 2 on the hall device.
Adjust the digital voltmeter to read 20 VDC and attach the red lead to pin 3 on the Hall device and the black lead to pin 2 of the Hall device.
Plug a 9-volt battery into the battery connector and attach it to the breadboard with the two rubber bands. The voltmeter should read approximately 2.5 volts without any magnetic field interference.
Place a magnet near the device and observe reading on the meter changing. To calculate the strength of the magnetic field, multiply the change between the calibrated zero reading (approximately 2.5 volts) and your current reading by 1,000 and divide by the Hall device's sensitivity. A positive result indicates a magnetic north pole and a negative result indicates a magnetic south pole.