Intermediate

Crystal Radio

Build a passive AM radio receiver that uses an antenna signal, tuned circuit, diode detector, and sensitive earphone.

Safety first, always.

ElectroLab AI teaches theory, low-voltage electronics, and planning concepts. Mains voltage, switchboards, fixed wiring, high-current systems, and legal electrical work must only be performed by licensed electricians where required.

Open Safety Center

Guided visual build

See it, place it, test it, then debug it.

Visual schematic

Crystal radio signal path

The antenna feeds a tuned LC circuit, then a diode detector extracts audio for the earpiece.

Low-voltage model

TP1: antenna

TP2: tuned circuit

TP3: detector audio

Power low-voltage projects from batteries or current-limited supplies first. Stop if a part heats, smells, sparks, or behaves unexpectedly.

Interactive build mode

Crystal Radio step-by-step

Move one build action at a time. Treat each step as a checkpoint before adding the next connection.

Progress

1 / 5

Current action

Wind or prepare the tuning coil.

Wiring focus

Stage 1 of 5

tuning coil

variable capacitor

detector diode

antenna/earth

station tuning

Identify the part and orientation before placing the next wire.

Do not use outdoor antennas near power lines or during storms. Keep antennas far from mains wiring.

Project test bench

Pre-flight, first power, and fault response.

Treat this like the bench checklist beside the project. Tick what is proven, then use the symptom picker if the circuit does not behave.

Readiness

Do not power this yet

Pre-flight checks

Power source voltage matches the project parts.Positive and negative rails are identified and not swapped.Polarized parts have been checked before power-up.A current limit, fuse, resistor, or safe supply protects the first test.Meter is set to the correct mode before touching probes to the circuit.Diode direction is known.Antenna and earth connections are safe and appropriate.Coil enamel is scraped clean at contact points.

Before power

Measure supply polarity and expected voltage at the rails.

During first power

Use current limiting and watch for heat, dimming, or voltage collapse.

After a fault

Power off, isolate one section, then measure from source toward load.

Build target

Explore resonance, detection, antennas, and radio waves without a battery.

Build steps

1.Wind or prepare the tuning coil.

2.Connect the coil and variable capacitor as a tuned circuit.

3.Add the detector diode from the tuned point to the earphone.

4.Connect a long antenna and a good earth or counterpoise.

5.Tune slowly while listening through a high-impedance earpiece.

What you are learning

1.The LC circuit resonates at selected radio frequencies.

2.The diode detects the audio envelope from AM signals.

3.Antenna length and grounding strongly affect signal strength.

Bench tests

1.Check coil continuity.

2.Try tapping the coil at different turn counts.

3.Compare day and night reception.

Fault finding

1.No stations: improve antenna, ground, or diode orientation.

2.Very quiet audio: use a high-impedance earphone or audio transformer.

3.Only one station: improve tuning range or coil spacing.

Upgrades

1.Add a simple audio amplifier after the detector.

2.Build a better variable capacitor mount.

3.Experiment with different coil diameters.

Project safety

Do not use outdoor antennas near power lines or during storms. Keep antennas far from mains wiring.