This is a basic circuit for a gold detector!
It uses magnets and electricity to see if there is a metal nearby, even gold.
The circuit makes a special kind of electricity that flows back and forth really fast.
This creates a magnetic field around a coil.
When any metal gets close, the electricity flow changes.
This simple project is a fun way to learn how metal detectors work, but it might not be the best for finding real buried treasure!
Circuit Working:
Parts List:
| Component Type | Description | Quantity |
|---|---|---|
| Resistors (All resistors are 1/4 watt unless specified) | 47k | 1 |
| 220Ω | 1 | |
| Capacitors | Ceramic 10nF | 1 |
| Ceramic 4.7nF | 1 | |
| Ceramic 1nF (each) | 2 | |
| Electrolytic Capacitor | 47µF 25V | 1 |
| Semiconductors | Transistor BC547 | 1 |
| Inductors/Coils | Search Coil 16 turns, 6″ diameter (12cm) | 1 |
| Other | Switch button | 1 |
| 9V Battery | 1 |
The schematic above is a simple metal detector circuit, which can detect gold, other metals and even coins it has limitations compared to more sophisticated metal detectors.
Here are some working details and additional data to consider:
The circuit creates an oscillating magnetic field around the search coil with a frequency of approximately 140 kHz.
When a metal object is brought near the search coil eddy currents are induced in the metal object, which can affect the inductance of the coil.
This change in inductance causes the oscillator frequency to shift.
The AM radio picks up a harmonic of the oscillator frequency as a beat or squeal.
When the search coil comes near a metal object the change in oscillator frequency causes a shift in the tone of the squeal.
The range of this simple metal detector is limited to a few centimeters depending on the size and type of metal object.
Also, it will likely pick up a lot of false positives from environmental factors like mineralized ground.
Here are some additional points to consider:
The radio needs to be tuned to a frequency close to a harmonic of the oscillator frequency to hear the beat or squeal.
There is no specific radio station to tune into as you are using the radio to detect a beat frequency created by the interaction between the circuit and the search coil.
The number of turns and the diameter of the coil will affect the frequency of the oscillator.
The coil in the schematic is specified as 6 turns with a 12 cm diameter, but you can experiment with different coil configurations to improve performance.
This circuit is battery powered and low voltage so it is generally safe to use.
However, as with any electrical project you should use common sense safety practices when building it.
Overall, this is a simple and educational project to learn about the basics of metal detection.
However, you should not expect performance comparable to commercial metal detectors.
Formulas:
Creating a sensitive oscillator that can identify variations in the grounds conductivity brought on by metal particles, such as gold, is the first step in designing a simple circuit for a gold detector.
Here is a simplified formula:
f or oscillation frequency:
The LC inductor capacitor tank circuit, which is produced with the search coil (inductor) and capacitors in the circuit, usually determines the oscillator frequency.
The oscillator frequency is affected when the search coil senses a change in inductance (caused by being close to conductive material such as gold).
f = 1 / 2π√L * Ceq
where,
- L is the search coils inductance.
- The equivalent capacitance of the capacitors in the tank circuit is denoted by Ceq.
Note:
This formula offers a theoretical foundation for comprehending the operation of a gold detector circuit and the roles played by resistors, capacitors and search coils.
Accurate detection results need careful calibration and adjustments to component levels.
How to Build:
To build a Simple Gold Detector Circuit follow the below mentioned steps:
- Connect base of the transistor Q1 to R1 47k resistor which is then connected to the positive side of the battery.
- Connect the collector of the transistor Q1 to two capacitors C2 and C3 1nF which is then connected to the positive side of the battery.
- Connect the emitter of the transistor Q1 to resistor R2 and the negative side of the battery.
- Connect resistor R1 and capacitor C1 in series from positive supply to negative supply.
- Connect a search coil one end to collector of Q1 and other end to positive supply.
- Connect a push button to positive supply of battery.
- Connect a capacitor C5 from positive supply to negative supply.
Note:
- This circuit is battery powered and low voltage so it is generally safe to use.
- However, as with any electrical project you should use common sense safety practices when building it.
Conclusion:
A simple gold detector circuit offers a glimpse into the world of metal detection using the concept of oscillating magnetic fields.
While it can find gold and other metals nearby its range is limited and it lacks the ability to pinpoint specific metals or overcome environmental noise.
However, building this basic circuit serves as a fun learning experience for understanding the core principles behind metal detection technology.