Metal Detector Circuit Schematic using Beat Frequency Oscillator (BFO)


Posted on Feb 7, 2014

The simplest method of detecting metal is by beat frequency oscillator. The circuit basically consists of two balanced oscillator. One acts as the detector element, the other provides the reference signal. This oscillator frequency reference is set to fix value, whilst the detector oscillator varies depending on the metal presence. The reference o


Metal Detector Circuit Schematic using Beat Frequency Oscillator (BFO)
Click here to download the full size of the above Circuit.

scillator can be constructed using various circuit topology: inductor-capacitor (LC), resistor-capacitor (RC), or even a crystal (quartz) oscillator. While the reference oscillator can be implemented using various circuit topology, the detector oscillator always use inductor-capacitor topology, because the mechanism will be using the magnetic induction property of the detected object, and the inductor component of the detector oscillator will be the detecting probe. With the absence of a metal near the detector probe (the inductor component of the detector oscillator), the detector oscillator is tuned to have same frequency as the reference oscillator. The output of the detector oscillator and the reference oscillator output is mixed using hetero-dyne mixer circuit, producing a beat frequency output of zero Hz, or a very low frequency if both oscillator is slightly unbalanced. In the presence of a metal near the detector probe, the detector oscillator will shift it`s frequency, and the mixer output will produce a tone with frequency equal to the difference of the reference and the detector frequency. The figure below shows one of the simple metal detector circuit. You can see the reference circuit is a simple RC circuit, and its frequency is determined by R1-P2-C1. The detector oscillator is an LC oscillator with the frequency is determined by the L1-C2-C3 values. The NAND gates use CMOS 4011 chip, a low power component...




Leave Comment

characters left:

Related Circuits

  • New Circuits

    .

     


    Popular Circuits

    Miniature Black and White TV System
    Motorcycle Alarm
    Oscilloscope triggered sweep circuit
    Pushbutton-Controlled Power Switch
    PS2 mouse and BASIC Stamp computer
    How to Increase TDA2030 Amplifier Gain PCB
    A SHORT WAVE REGENERATIVE RECEIVER
    Peripheral circuits MIC5158 a simple 5V input 3.3V 10A output linear regulator circuit



    Top