This is a simple metal detector circuit, Can find various metal and adjustable sensitivity Easy to use to place near metal. The circuit inside includes a few components has IC-NE556 is at the heart of the circuit, with a principle of Monostable multivibrator then show on Moving Coil Type Meter. Though very ancient, it still has many uses.
The working principle
This project use principle of two thin metal sheets at install is under this tool parallel to the metal sheet that we want to find, as Figure 1 Which will appear a virtual capacitor. By one metal sheet will connect to pin 8,12 of IC1/1. And next metal sheet will connect to ground of circuit as Figure 2 We so have the capacitor connect with IC1/1 so making IC1/1 as the astable multivibrator continuously generate the frequency.
Figure 1 The capacitors virtual. Which caused from parallel of metal.
The capacitance virtual varies according to the type of metal found and a distance between the metal pieces to this tool. The changing of the capacitance virtual will cause The frequency signal that generates from IC1/1(NE556) will also change with.
The signal from pin 9 of IC1/1 goes to pin 6 of IC1/2. Which is connected as (Monostable multivibrator) To produces square wave out to pin 5 in each time that has triggering from IC1/1.
The signal from pin 5 of IC1/2 will be changed signal when sending through resistors-R4 and capacitor-C4 will be filtered become to direct current voltage to meter-M1. To display of finding to show us. The DC voltage level that changed follows by the capacitance virtual.
We can adjust sensitivity by VR2 and VR3 is offset voltage-controller to a meter needlepoint at zero, or full scale on the left. To compensate for the display of the meter can be easier.
When understanding the working principle of this project already. The next step is creation First, the equipment you need to buy before. Then builds the PCB as Figure 3 show Actual-size, Single-sided PCB layout.
The parts list.
IC1: NE556, Dual timer
0.25W Resistors, tolerance: 5%
R3,R4: 470 ohms
C1,C2: 2.2uF 16V, Electrolytic
C6: 47uF 16V, Electrolytic
VR1: 50K horseshoe-shaped variable resistor
VR2: 50K, potentiometer
VR3: 1K, potentiometer
C3: 1000pF 50V ceramic capacitor
C4,C5: 0.022uF 50V Mylar capacitors
M1: 200uA size Meter or VU meter
Next, assemble various components similar in Figure 4 should put a low component before such as the resistors Accordance with the following equipment height, and do not forget to be careful about the legs of the device and the value of it.
Then later assemble the circuit successfully and fully check circuit. Then press switch power on to circuit, and then adjust sensitivity (VR2) to full left. And rotate adjust offset (VR3) to fully right.
Next, see the meter needle do it deflect? If it does not deflect so adjust VR1 on PCB. You will see the meter needle deflect up. Then adjust VR1 maximum scale, net step needle will fell so stop adjusting
Later adjust VR2 to right and see meter needle must to right as adjusting, and try to adjust VR3 to the left to see what the meter needle to the left will be caught by the fine as well. Adjust VR2 and VR3 finished to its original position. It indicates that the circuit is working perfectly.
For this project can check objects with property Is it the metal? By the when we want to find metal. First, setting VR2 and VR3, press switch for power on.
Then, adjust VR3 to the left. To turn the meter needle to the left of the meter scale. Nearly end scale to the right and then to adjust VR2. To turn to the right hand of modest scale. Then adjust VR3 back to the left again. To turn the meter needle to the left again at the same location. Just this tool is available to find metal.
When found metal the meter needle will turn up. If the meter needle hit too hard, after finding metal, adjust VR2 reduced. This tool can be applied to many applications. For example, use looking for steel beam with a ceiling covered. Etc.
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