This is Stray Magnetic field meter circuit,using LED display.
Electronic technology is common. Although it has much useful. But it is a kind of environmental pollution. Which is called “Electomog” or we will called Stray Magnetic fields (SMFs). And, Some experts said that “SMFs” has the effect to the human body.
The SMFs that is referenced in this project will be low frequency is in range of 200-1200 Hz. The Effects of SMFs. Could be caused by a monitor computer and high voltage cable. This meter that can use to measure the magnetic field to find a source of the magnetic field so can Avoid and to have a minimal effect.
There are a lot of people believe that the strong magnetic fields, that can cause side effects to people exposed to it. During the years 1988-1990, has a number of organizations. In Europe and North America that cause fears have explored the possibility of between the magnetic field. and Results that will make people sick or Discomfort as (cancer or diseases associated with the central nervous system) example: Causes Sclerosis.
In America and Sweden has legislated that. Do not manufacture power supplies with magnetic fields up to 200-300nT. In many countries they do on the computer monitor must be standard MPRII and TCO. Which defines the maximum magnetic field that is emitted from the device. If you feel fear about the effects of the magnetic field. To check the system that generates the magnetic field and the magnetic field. It will be in the range 100nT-2.3uT. Measurement will be the distance actually like while you are working on your computer screen to measure the position of your head etc.
The principle of meter is shown a block diagram in Figure 1 the induction coil was used to detect the magnetic field. Which output that get is AC volts about 1uV And this output will be amplifier up to 101 times by Op-amp X1
Figure 1 Block Diagram of stray magnetic fields meter circuit.
The Op-amp will be connected with the integrator circuits are X2. Which will serves as the frequency-dependent amplification. The resistors R4-R6 will acts to feed back, to ensure that the operation of the circuit is stable. And another Another reason is if using cheap equipment the circuit will not work well, so have to the feed back and must to ensure that maximum gain is x101 (1+R6/R5) this value of R6/R5 also set minimum frequency range.
The circuit of this meter is shown in Figure 2 which it consists of many parts of the input signal amplifier, integrated circuit, automatically feed back circuit, rectifier circuit, the display circuit and final the power supply.
The input amplifier circuit will use IC1a will be a signal amplifier from L1-inductor coil. This signal will be amplified up about 101 times
The integrator circuit will use an IC1b. And the rectifier circuit will use IC1c, this really circuit is a differential amplifier circuit, which the averaged voltage from output of the integrator circuit that very less, thus the output power energy so nonlinear, is a half wave rectifier of AC voltage with R16, C6. In case that use digital meter, will use the value of R18-R20 and C7. A various factor value will cause correcting and is determined with the rectifier circuits. Therefore, this OP-amp must swing over IC1a or IC1b.
Both op-amp IC1a and IC1b will take only the sine wave signal. Which will get the signal that is a D.C. about 3V. The IC1c will get about 0-volts. Meaning of Op-amp can amplify the signal of 2.2 times.
The voltage drop across C6 will be used by the display driver circuit by IC2, which will show the density (strength) of the magnetic field. The driver will have its reference voltage and the power supply voltage. The voltage of 1.25 volts, a voltage is applied to both OP-AMP IC1a and IC1b the voltage at point A has value as follows:
[(R14+R15) / R15] x 1.25V = 3V
The least voltage that IC2 will use drive is 1.2V. Therefore IC will be driven with an average differential voltage of signal value, that will use as 1.2×3.141 = 3Vp-p. Because the amplification is done at that rectifier circuit is The OP-AMP will have the widest range of the amplifier. The voltage of the battery will not effect the meter.
The display driver will control 10 LEDs. The circuit is indicated clearly. Which LED will show the intensity of the magnetic field. When LED D10 glow. Measuring the intensity of the magnetic field > 2.3uV. Which maximum more value that set in MPRII (250 nT). If the meter is connected into the digital voltmeter will have to install the rang of a meter at DC volts at 200 mV. The measuring range is 50nT-2uT.
How to build this project.
The PCB is built has been successfully created, as Figure 3. and Figure 4 is the component layout. The induction coil is the work you have done with caution. The core of the coils are made with a sheet of PCB 2 splice plates, similar to a sandwich. But separated by wire size 1.3 mm. = 4 pcs. And solder inlet position makes. And take a pair plate splice into the mainboard. The dual point to joint with coil 2 points and point 3 Are provided to make the forces between two plates attached to the mainboard and more athletic.
The coil winding 121 turns and use coil with diameter 0.2 mm. The coil is wrapped, it is about 5 layer. Finished solder between the mainboard with the board of the coil at that point prepared the 3 point.
After that, it consists of various devices with its position. Careful the polarity of the capacitor and other devices. The IC: you will directly soldering with PCB Or will also use the socket as well.
End devices are LEDs, these diodes will be divided into three groups. Each group will have a different color. D1-D3 use green will show safe levels. D4-D6 use yellow will show untrusted. and D7-D10 use Red color indicates the level of danger. After S1-switch and 9-volts battery is connected successfully. The circuit is ready to use.
Meter Range (LED) : 100 nT – 2.3 uT
Scale : The logarithm
Meter range (DVM) : 50 nT – 2 uT
Scale : Linear
Frequency range : 40 Hz – 10 kHz
(+ 1.5 dB)
The maximum error of 5%.
Current drain 10 mA
The power supply: 9-volts
T = tesia is A unit of magnetic flux density in the system.
SI unit is equal to 1 weber m-2.
The part you will need
Resistors ¼ watts
R1, R9, R11*, R14: 10K
R2*, R5, R7*: 1K
R3*, R6, R16: 100K
R4, R8: 1M
R10, R12: 22K 1%
R13: 100 ohm
R18, R19*: 39K
R20: 82K 1%
R is the resistor values ??marked with * 1% mistakes.
C1, C7: 100uF 16V, Electrolytic
C2: 10nF 50V, Polyester
C3: 4.7uF 16V, Electrolytic
C4: 10uF 16V, Electrolytic
C5: 47pF 50V, Ceramic
C6: 2.2uF 16V, Electrolytic
C8: 100uF 16V, Electrolytic
IC2: LM3915, Dot/Bar Display Driver
D1-D3: LED: Green
D4-D6: LED: Yellow
D7-D10: LED: Red
D11: 1N4148, 75V 150mA Diodes
L1 see text.
Holder battery and 9V battery
ON/OFF Switch etc.
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