Single Chip AM Radio Circuit

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The ZN414 IC contains an entire automatic gain controlled AM receiver in a small three pin package. With only a few external components, a simple radio with excellent selection and reception can be constructed. Since the chip also uses a low supply voltage of only 1.3V, 3V coin cell battery can make for a physically small circuit with many covert uses. The chip has a wide bandwidth of between 150KHz and 3MHz, so by playing with values in the tuning circuit you can pick up a wide variety of signals.

Schematic

Parts

Part	Total Qty.	Description	Substitutions
R1	1	100K 1/4W Resistor
R2	1	470 Ohm 1/4W Resistor
R3	1	1K 1/4W Resistor
C1	1	0.04uF Ceramic Disc Capacitor
C2	1	365pF Variable Tuning Capacitor
C3	1	0.01uF Ceramic Disc Capacitor
D1, D2	2	1N4148 Signal Diode
U1	1	ZN414 Radio IC	MK484
L1	1	See Notes
MISC	1	Board, Holder For Batteries, Wire, Coil Form For L1

Notes

The ZN414 is obsolete. The MK484 is it's replacement, but like all special purpose ICs, it can be hard to find. At the time of this writing, there are many suppliers online that carry the IC. The ZN416 is functionally the same but with the additiion of a built in headphone amplifier.

L1 is made by winding 40 turns of 28 AWG magnet wire around a 4" non-magnetic coil form. Cardboard tubes or paper cups are ideal forms.

The audio output of the circuit is about 0.1V peak to peak, which will drive a set of crystal earphones or other very high impedance phones. A small audio amplifier made with an LM386 will allow you to use modern dynamic headphones or a small speaker.

L1, C1 and C2 are the tuning circuit. By changing them around, you can change the range of frequencies the radio is capable of. Easiest to change is L1. Simply by altering the number of coils or moving the windings farther apart, you can shift the circuit to different frequency ranges.

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