Making half-duplex walkie talkie with LM386

Click to download: LM386.pdf

The walkie-talkie has low cost and simple circuit, and can be used for intercom in different rooms of the office and baby room monitoring. The talking distance can reach 2Km.
working principle

The circuit principle is shown in Figure 1 (click here to download the schematic). This circuit can only be used for "half-duplex" intercom, that is, only one party can speak and the other party can listen between the host and the extension, but not both. Listening and speaking are switched by switch S1, which is set at the host. The location of S1 shown in the figure can be spoken by extension and the host listens; if S1 is dialed down, it will become spoken by the host and listen by extension. There is only one speaker BL2 on the extension side, which acts as both a microphone and an earpiece. The same is true of the host speaker BL1. LM386 is used as a power amplifier. The signal is input from the pin â‘¢, the signal is output from the pin â‘¤, and the capacitor connected to the pins â‘ and â‘§ can adjust the circuit gain. The power supply voltage can be from 4.5-9V.
See the table below for component selection and component list.

Numbering	name	model	Quantity
R1	resistance	10K	1
C1, C3	Electrolytic capacitor	10u / 16V	2
C2	Electrolytic capacitor	100u / 16V	1
IC	Power amplifier integrated circuit	LM386	1
S1	switch	Double pole double throw	1
BL1, BL2	speaker	8Î© 0.25W	2

It is better to use twisted pair for the BL2 outgoing line to reduce interference. If necessary, a power switch can be added to avoid time and space power consumption. The disadvantage of this circuit is that the extension cannot call the host.

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