Hello
again.. This time I’m going to tell you how to make a very simple metal
detector with a minimum cost. I made this with a group for a module of my
degree program. The basic circuit we took from the internet and did some
modifications according to my requirements.
For this we needed few devices as below.
NE555
47kΩ resister
2.2 μF, 3.3 μF, 10 μF capacitors
Speaker (8Ω resistance)
Copper wires of 0.3mm in diameter
9V battery
Switch
Connecting wires
Here we used a 555 IC and it gives accurate oscillations and
these oscillations are controlled by the capacitor network and inductor used in
the circuit. When the inductor goes near the metal the inductance change and
frequency varies according to that. Therefore when the inductor meets a metal
it gives out a different sound from the speaker.
This is the basic circuit for the metal detector and we
changed few capacitor values from the original circuit.
FIGURE 1: BASIC CIRCUIT
All the components like resisters, speaker, capacitors and IC
can be obtained easily but when comes to the inductor it becomes more complex. When
making the inductor we used copper wires with 0.3mm diameter. Then we wound the
copper wire around circular rig foam for 200 turns. This rig foam circle has a
diameter of 15cm and height of 1.5 cm. We got these values why doing few
calculations and tests.
To find a suitable diameter for the inductor we used
inductors with few different measurements and connected it to the above circuit
and checked the accuracy by measuring output frequency. We found that with the
increment of the diameter the accuracy also increasing. So we selected 15cm. Then
we removed an inner circular portion from the rig form to make it air core and by
using equation 1 below, we calculated the number of turns of the inductor.
L
– Inductance
D
– Diameter
N
– Number of turns
H-
Height
According
to the circuit we could get 10mH inductance by 187 turns. But for better
inductance we used 200 turns which gives an inductance of 11.5mH.
FIGURE
2: INDUCTOR
After
making the inductor the circuit in Figure 1 can be connected to the project
board and test it. We did not use PCB because this is a simple circuit. We made
the circuit on a dot board as below.
FIGURE
3: CIRCUIT MOUNTED TO THE DOT BOARD
Now
the basic metal detector is ready. To give a better finishing for the device we
made a box with Perspex and attached the circuit on the dot board, batteries,
switch and speaker to that box.
FIGURE
4: COMPONENTS FIXED TO THE PERSPEX BOX
Then
we connected this box to the wood handle of the detector and then we connected
the inductor to a plastic plate and that plastic plate connected to a rod.
FIGURE
4: PERSPEX BOX CONNECTED TO THE ROD
FIGURE
5: completed metal detector
This
is a very simple metal detector and this can be improved in many aspects like technically,
appearance etc. Anyway from this post you
can get the fundamental understanding about
a metal detector and let’s meet with another post soon. Thank you for
reading..
Special thanx to Sampath and Amila...
Special thanx to Sampath and Amila...