How to Make a Simple Metal Detector Circuit

Updated 5 November 2026 · Standard formula, shown below

A simple metal detector circuit can show how a changing magnetic field affects an oscillator: bring metal near its search coil and the circuit’s tone may shift. This beginner build uses a timer IC, a small audio amplifier and a hand-wound coil; it detects nearby metal rather than identifying or measuring it precisely. Gather the parts and soldering tools below, and work from a low-voltage battery.

What You’ll Need

One NE555 timer IC and an 8-pin socket (recommended)
One LM386 audio amplifier IC and an 8-pin socket (recommended)
One 100 kΩ linear potentiometer for sensitivity, one 10 kΩ resistor, and one 1 kΩ resistor
One 10 nF capacitor for the timer and one 100 nF ceramic capacitor for supply decoupling
One 10 µF electrolytic capacitor for the amplifier input and one 220 µF electrolytic capacitor for its output
One 8 Ω small speaker or piezo sounder compatible with the amplifier output
About 1 m of insulated copper wire, 0.3–0.5 mm in diameter, for the coil
A 9 V battery and clip, solderless breadboard or perforated board, hookup wire, and a nonmetallic coil former about 10 cm across
Wire cutters, a soldering iron and solder if using perforated board, and a multimeter

Use this as a basic experimental circuit, not as a guaranteed detection range or finished outdoor instrument. Keep the coil, wiring and circuit away from mains wiring; disconnect the battery before changing connections.

Step-by-Step

Make the search coil. Wind 25 turns of insulated copper wire around a roughly 10 cm nonmetallic former. Leave 10 cm leads at both ends. Remove insulation from the lead tips and check with a multimeter that the winding is continuous and not shorted to nearby conductors. Secure the turns with tape, then remove or leave the former in place. Keep the coil flat and its turns close together.
Build the timer oscillator. Place the NE555 across the breadboard’s center gap, with its notch identifying pin 1. Connect pins 1 and 8 to ground and +9 V respectively; connect pin 4 (reset) to +9 V. Join pins 2 (trigger) and 6 (threshold). Connect the 10 kΩ resistor from +9 V to pin 7 (discharge), and the 100 kΩ potentiometer between pin 7 and the joined pins 2 and 6. Wire the 10 nF capacitor from pins 2/6 to ground. Add the 100 nF capacitor between the supply rails close to the IC.
Connect the coil into the timing network. Connect the search coil between the joined pins 2/6 and ground, in parallel with the 10 nF capacitor. The coil and capacitor form the frequency-setting network; nearby metal can alter the coil’s inductance and shift the oscillator. Because component tolerances and coil construction affect the circuit, the tone and sensitivity will vary between builds.
Wire the audio stage. Put the LM386 across a breadboard gap. Connect pin 4 to ground and pin 6 to +9 V. Connect the 1 kΩ resistor from the NE555 output (pin 3) to LM386 pin 3, the non-inverting input. Connect LM386 pin 2 to ground. Connect the speaker between pin 5 and ground through the 220 µF electrolytic capacitor: its positive lead goes to pin 5 and its negative lead to the speaker. Connect the 10 µF capacitor from pin 3 to ground if the audio input is too noisy; its positive lead goes to pin 3. Check the polarity markings on electrolytic capacitors before powering up.
Check every connection before adding power. Confirm the IC pin numbers, supply polarity and ground connections against the pinout diagrams for the specific parts. Make sure no wire or component lead bridges adjacent breadboard rows. If you are using a soldering iron, work in a ventilated area, use eye protection, and let hot parts cool before handling.
Power on and find a stable tone. Connect the 9 V battery. The speaker should make a tone or buzz. Turn the potentiometer slowly through its range until the tone is clearly audible and steady. Do not leave the circuit connected if the IC or battery becomes hot, or if you smell burning; disconnect the battery and inspect for a short or reversed connection.
Test and tune the detector. Hold the coil several centimetres from metal objects, then move a coin or steel object toward it. Listen for a change in pitch or loudness. Adjust the potentiometer to make the response easier to hear, then move the coil away and confirm the tone returns. Keep your hands and other metal objects away from the coil during comparisons.
Make the build more robust. Once it works on a breadboard, transfer it to perforated board and keep coil leads short. Secure the coil to a nonmetallic handle and strain-relieve its wires. Test again after moving it: nearby batteries, speaker magnets, solder joints and metal fasteners can affect the response. Avoid enclosing the coil in metal.

Common Mistakes

Misreading IC pin numbers: Viewed from above, pin numbers run counterclockwise from the notch. Recheck the package orientation before connecting power.
Using a steel coil former: A metal former changes the coil’s behavior and can cause a false or constant response. Use plastic, cardboard or another nonmetallic material.
Expecting a long range: This simple circuit is sensitive to its coil, wiring and surroundings. It is best treated as a close-range demonstration; it will not reliably find deeply buried objects.
Reversing electrolytic capacitors: Check the marked negative stripe and the circuit’s positive connection. Incorrect polarity can damage a capacitor.
Changing several parts at once: That makes faults harder to isolate. Change one connection or adjustment, then test again.

Tips

Use fresh battery power and keep the supply and coil leads separated where possible.
Move the test object at a consistent distance and speed. A repeatable test makes small tone changes easier to notice.
Try different objects, such as a coin, steel washer and aluminum foil, but do not expect the circuit to identify the metal type.
Keep the coil still while adjusting the potentiometer. Handle movement and nearby objects can also change the sound.

Troubleshooting

No sound: Check battery voltage and polarity, then verify the LM386 pinout, speaker connection and electrolytic capacitor orientation. Confirm that the NE555 output at pin 3 is changing; a multimeter may show a varying or averaged voltage, though it cannot display the audio waveform clearly.
Constant loud buzz or unstable tone: Check for loose breadboard connections, long coil leads, a poor ground, or a coil near metal. Add the 100 nF capacitor close to the IC supply pins and shorten wires.
Sound works but metal makes no obvious difference: Test with a larger metal object close to the coil, away from other metal. Adjust the potentiometer slowly and check that the coil has the intended turns and continuous wire. A different coil or component tolerance may be needed.
Parts heat up or the battery drains quickly: Disconnect immediately. Look for a short between +9 V and ground, an incorrectly placed IC, or a speaker connected directly across the supply. Do not reconnect until the fault is corrected.

Frequently Asked Questions

Can this circuit detect gold?
It may respond to a gold object if it is close enough, but it cannot distinguish gold from other metals. Response depends on object size, shape, distance and the coil.

How deep can this detector find metal?
There is no dependable fixed depth for this simple design. Small objects are generally detectable only very close to the coil; larger objects may affect it farther away.

Can I use a different battery?
Use a stable supply within the voltage limits in the NE555 and LM386 datasheets. Do not assume a higher voltage is safe; check both parts and the speaker rating first.

Why does the tone change when I touch the coil?
Your hand and nearby objects can alter capacitance or pick up electrical noise. Keep the coil leads short and avoid touching the winding while testing.

Can I connect headphones instead of a speaker?
Not directly without checking the headphone impedance and output level. The LM386 output can be too loud for headphones; use a suitable output control and start at minimum volume.

Method: the standard formula for this calculation, rounded as each result states. See how the calculators work or report an error.