Theme: Development of Arduino Metal detector Contents: Introduction

Circuit Diagram:
We have used an Arduino Nano for controlling whole this Metal Detector Project. A LED and Buzzer are used as metal detection indicator. A Coil and capacitor is used for the detection of metals. A signal diode is also used for reducing the voltage. And a resistor for limiting the current to the Arduino pin.


Working Explanation:
Working of this Arduino Metal Detector is bit tricky. Here we provide the block wave or pulse, generated by Arduino, to the LR high pass filter. Due to this, short spikes will be generated by the coil in every transition. The pulse length of the generated spikes is proportional to the inductance of the coil. So with the help of these Spike pulses, we can measure the inductance of Coil. But here it is difficult to measure inductance precisely with those spikes because those spikes are of very short duration (approx. 0.5 microseconds) and that is very difficult to be measured by Arduino.

So instead of this, we used a capacitor that is charged by the rising pulse or spike. And it required few pulses to charge the capacitor to the point where its voltage can be read by Arduino analog pin A5. Then Arduino read the voltage of this capacitor by using ADC. After reading voltage, the capacitor quickly discharged by making capPin pin as output and setting it to low. This whole process takes around 200 microseconds to complete. For better result, we repeat measurements and took an average of the results. That’s how we can measure the approximate inductance of Coil. After getting the result we transfer the results to the LED and buzzer to detect the presence of metal. Check the Complete code given at the end of this Article to understand the working.
Complete Arduino code is given at the end of this Article. In the programming part of this project, we have used two Arduino pins, one for generating block waves to be fed in Coil and second analog pin to read capacitor voltage. Other than these two pins, we have used two more Arduino pins for connecting LED and buzzer.
You can check the complete code and Demonstration Video of Arduino Metal Detector below. You can see that whenever it detects some metal the LED and Buzzer start to blink very fastly.