Pulse Induction Metal Detectors

Spirit PI wireless metal detector based Arduino

Spirit pi wireless metal detector based Arduino is an impulse metal detector. This metal detector is based on an Arduino or esp32 micro-controller and a smartphone. this metal detector is easier to assemble although it contains more parts than vlf detectors  like “smart hunter” because we don’t need to adjust the coils and adjust the balance of the coils. In this metal detector we only use one coil, which is both TX transmitting and RX receiving. One coil sends a signal and then receives it. this type of metal detector (pulse) operates at a very low frequency, only around 60 hz, which makes it easier for us to process the signal, for example with an Arduino micro-controller.
To make it wireless, it decided to use the hc-05 Bluetooth module and thus send the data received from the coil to the smartphone. To process the data in the smartphone, that will use a new application called “spirit pi” wireless metal detector.

Components list for Spirit wireless metal detector based Arduino:

  • Arduino (nano, mega, uno, etc.) or ESP32 micro-controller
  • Bluetooth module HC-05 or HC-06
  • Smartphone (android 4.4 or higher)
  • Copper enameled wire 0.4 – 0.7 (for winding 25 turns on a circle with a diameter of 20 cm)
  • Transistors BC547 and BC557
  • Operational amplifier TL072
  • C3 – Capacitor (1000uF 16V)
  • C2 – Capacitor (10uF 16V)
  • C1 – Capacitor (1uF 16V)
  • Two diodes N4148
  • R1, R3 – resistances (1kΩ 1/4w)
  • R2 – Resistance (6.8kΩ 1/4w)
  • R4 – Resistance (100Ω 1/4w)
  • R5 – Resistance (150Ω 1/4w)
  • R7 – Resistance (220Ω 1w)
  • R6 – Resistance (390Ω 1/4w)
  • R9 – Resistance (62kΩ 1/4w)
  • R8 – Resistance (2MΩ 1/4w)
  • R11, R13 – Resistances (100kΩ 1/4w)
  • R10, R12 – Resistance (47kΩ 1/4w)
  • R14 – Resistance (10kΩ 1/4w)


Assembling the circuit board for the Spirit metal detector based Arduino

The first step we need to do is prepare everything before assembling on the PCB. All the components are ready to use, we just need to upload the firmware to the Arduino and increase the baud rate of the HC-05 Bluetooth module .
Before uploading the main code to Arduino, we have to upload a small code to help us choose the baud rate of the hc-05 Bluetooth module and change the Bluetooth module name.
This method is only suitable for the hc-05 Bluetooth module . If you have another Bluetooth module like hc-06 , you can search in the internet, there is a lot of information on this topic.
First take Arduino and connect it to PC . Download the code that you find here, the code is called “Sketch_commands_at”. Once the sketch is uploaded, we connect the Bluetooth module. The Tx pin of the Bluetooth module is connected to digital pin 10 of the Arduino, and the Rx pin of the Bluetooth module is connected to digital pin 11 of the Arduino.
To enter the AT command mode of the Bluetooth module, we have to do the following:
We press the button on the HC-05 Bluetooth module at the same time as turning on the power. The LED will start blinking slowly, which means it is in AT mode and we can send AT commands to the Bluetooth module. Now we open the program Arduino IDE and open Serial Monitor which you can find in Tools. On the Serial Monitor, make sure ” Ambos NL & CR ” and ” 38400 baud ” are displayed .
Now we write: ” AT ” on the monitor of the series and press Enter . If we did everything correctly, the message ” OK ” should appear , if it does not appear, look at the previous steps.
If your answer is “ OK, ” we can now change the baud rate. We write the following:
AT + UART = 115200,0,0 and press enter, if everything goes well, the message “ OK”, Which means the baud rate has been changed successfully. The next step is to change the name so that a friendly name appears on our smartphone. We write AT + NAME = Spirit PI and press enter. The message ” OK ” should appear again . Ready! We have already changed the baud rate and the name of the Bluetooth module.
In the next step, we will need to make a circuit and upload the main sketch to the Arduino. At the moment we can disable the Bluetooth module and the Arduino, we will need them in the next step.

Download sketch for AT command Bluetooth module

Now we will prepare all the necessary components. In the previous step, we configured the Bluetooth module, and now, before proceeding with the assembly of the circuit, we need to upload the main sketch to the Arduino. If you have not yet configured the Bluetooth module, return to the previous step. The main sketch can be found here under this description. After loading the main sketch, we solder all the components, following as shown in the diagram. If everything is done correctly and there are no errors, the metal detector is immediately ready for use and does not need to be adjusted. Before testing, you need to connect the APP to the Bluetooth module. You can see how to connect the Bluetooth module with your smartphone.After connecting the Bluetooth module, we go to the connection of the ” Spirit PI ” application (Bluetooth must be activated) and open the settings. In the settings, select ” Select Bluetooth module “. In the window that appears, we select the name of our Bluetooth module. It should be “Spirit PI”. Ready !! From now on, when you open the app, just click the Connect button and the app will connect to the coil.

The schematic diagram

Below you can find a schematic diagram and a basic sketch for Arduino.

Spirit PI wireless metal detector based Arduino

Download the main sketch for Arduino

Scheme for version 2.0.0 on ESP32:

The best results can be achieved by replacing the Arduino with an ESP32 micro-controller. The ESP32 is more powerful and also has a built-in Bluetooth module, so the circuit will be more compact. The cost of esp32 is not much higher than that of Arduino, but if we take into account that we do not need to buy a Bluetooth module, it turns out that ESP32 is cheaper than Arduino. The sketch for the ESP32 is slightly different and we cannot upload the sketch from the Arduino to the ESP32, if you do not see the download link for the sketch for the ESP32 it will be available soon. In the diagram below, you can clearly see that it is not very different from the circuit on the Arduino.
Spirit PI wireless metal detector based Arduino

Spirit PI wireless metal detector based Arduino

Spirit PI wireless metal detector based Arduino

Download sketch and PCB for ESP32

The Coil construction :

The coil is pretty simple and only has 25 turns. To increase the sensitivity, you can try increasing or decreasing the number of turns. In the next video tutorial, you can see how this is done. There are several ways to make a reel, but I like the one I use in the video. The coil diameter is 20 cm and the enamel wire thickness is 0.7 mm. We can use from 0.5mm to 0.7mm.

Link to Android Application




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