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Designing Mini Megaphone Circuit Using LM386


A megaphone, also known as a bullhorn or loudhailer, is a device that amplifies sound, typically a person's voice, to be heard over greater distances. It's a cone-shaped acoustic horn that's portable and easy to use. Here designed a mini megaphone circuit using a single Op-Amp LM386 and some discrete components, which makes it a useful, portable, and very cost-effective solution.

Components List

The following components are required to make this diy mini megaphone:

  1. U1: LM386N Low-voltage audio-power amplifier IC - 1 pcs.
  2. Q1: Electret mic 9x6mm - 1 pcs.
  3. R1: 2.2kΩ 1/4W Resistor - 1 pcs.
  4. R2: 10Ω 1/4W Resistor - 1 pcs.
  5. R3: 10kΩ Trimmer potentiometer - 1 pcs.
  6. SW1: Tactile push button switch 6x6x5mm - 1 pcs.
  7. C1: 220nF Ceramic capacitor - 1 pcs.
  8. C2: 100nF Ceramic capacitor - 1 pcs.
  9. C3, C4: 470uF 16V Electrolytic capacitor - 2 pcs.
  10. SPKR1: 8Ω Horn speaker - 1 pcs.
  11. J1, J2: 2-Pin Screw terminal connector - 2 pcs.

Mini Megaphone Circuit Diagram

The schematic of diy mini megaphone circuit using lm386 is shown below.

Schematic of Mini Megaphone Circuit using LM386

The working principle of the mini megaphone circuit is simple. The main component of the circuit is the popular LM386 (U1), which is used to drive low-impedance loads such as an 8Ω speaker, and operates on a single supply voltage ranging from +4 to +12 V. The complete Technical Details can be found in the LM386 datasheet .

When the user presses the push button, the input DC voltage turns on the circuit. The input voice from the electret microphone (Q1) is converted into a signal, which is then fed into a non-inverting operational amplifier (Op-amp) circuit. This Op-amp amplifies the sound through an external horn speaker (SPKR1), allowing it to be heard over greater distances. The output sound volume can be regulated using a trimmer potentiometer (R3).

Mini Megaphone PCB Design

Assemble the circuit on a PCB as it saves time and minimizes assembly errors. An actual-size, single-side PCB with component layout for the mini megaphone circuit is shown below. Carefully assemble the components and double-check for any overlooked errors.

Top Silk Layer of Mini Megaphone PCB Bottom Copper Layer of Mini Megaphone PCB
Mini Megaphone PCB Layout. A PCB for the mini megaphone circuit.

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