Small Loudspeaker for Computer or Cell Phone

Small Loudspeaker is a fun project to do, you can connect it to your Cellphone or Laptop through a 3.5mm audio jack and can enjoy your own loudspeaker. You can also connect it to any device which has a 3.5 mm audio output, like TV, music player, video games etc. We have used LM386 IC to amplify sound, with a few external components.

LM386 is a low voltage audio amplifier and frequently used in battery powered music devices like radios, guitars, toys etc. The gain range is 20 to 200, gain is internally set to 20 (without using external component) but can be increased to 200 by using resistor and capacitor between PIN 1 and 8, or just with a capacitor. Voltage gain simply means that Voltage out is 200 times the Voltage IN. LM386 has a wide supply voltage range 4-12v. Below is the Pin diagram of LM386:

Pin description of LM386 along with the functions of external components used for amplification:

PIN 1 and 8: These are the gain control PINs, internally the gain is set to 20 but it can be increased up to 200 by using a capacitor between PIN 1 and 8. We have used 10uF capacitor C1 to get the highest gain i.e. 200. Gain can be adjusted to any value between 20 to 200 by using proper capacitor.

Pin 2 and 3: These are the input PINs for sound signals. Pin 2 is the negative input terminal, connected to the ground. Pin 3 is the positive input terminal, in which sound signal is fed to be amplified. We have connected one terminal of 3.5 audio jack to this input PIN 3 and the other terminal to Ground. 3.5 mm Pin is further connected to the Laptop’s audio jack.

3.5 mm stereo audio jack is found in mostly headphones, there are generally two types 3.5 mm audio Jack, TRS (TIP RING SLEEVE) and TRRS (TIP RING RING SLEEVE). In TRRS one extra terminal is generally for Microphone. We have used TRS audio jack here and soldered two wire to it, one to Ground (Sleeve) and other to Right audio (Ring) . You can understand by below images:

Pin 4 and 6: These are the power supply Pins of IC, Pin 6 for is +Vcc and Pin 4 is Ground. The circuit can be powered with voltage between 5-12v.

Pin 5: This is the output PIN, from which we get the amplified sound signal.

The output signal has both AC and DC component, and DC component is undesirable and can’t be fed to Speaker. So to remove this DC component, a capacitor C2 of 220uF has been used.

Along with this capacitor, a filter circuit of Capacitor C3 (.05uF) and resistor R1 (10k) has been used at the output PIN 5. This filter also called the “Zobel network”, this electronic filter is used to remove the sudden High frequency oscillations or noise.

Pin 7: This is the bypass terminal. It can be left open or can be grounded using a capacitor for stability.

Components

• IC LM386
• 3.5 mm audio Jack
• Speaker 8ohm
• Capacitors- 220uF, 10uF (two), 0.05uF
• Resistor- 10k
• Battery 5-12v

Circuit Diagram and Explanation

I have cut the male to male 3.5 mm audio jack and solder two wires, but one should a female 3.5 mm audio jack for bread board. And connect one end of male to male audio jack to female audio jack and other end to computer.

This circuit is quite similar to my previous circuit “LM386 Based Audio Amplifier Circuit”, we just replaced the Condenser Mic with the 3.5 mm audio jack to provide the input sound. Also potentiometer has been removed, because there is already a sound control in computer’s Music player.

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