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Raspberry Pi LM386 1W Battery Powered Audio Amplifier

2013-06-23 10:07 By Jason Birch

A low cost, simple, audio amplifier which can be used on a battery powered Raspberry Pi microcomputer. Using an LM386-4 audio amplifier integrated circuit. The power consumed during silence is ~5mA.

The video here demonstrates the project which this article describes how to build.

The article breaks the project down into several stages:

  • Circuit
  • Build
  • Project Costing


Circuit for Amplifier

The LM386 can operate on voltages between 4V and 12V which makes it idea for battery powered applications. When developing the circuit on a breadboard, I powered the circuit using a 9V NiMH rechargeable PP3 battery. In use on my project the circuit powers from 6 x AA NiMH rechargeable batteries, which comes to approximately 7.2V. The 5V supply to the Raspberry Pi should also be able to power the amplifier as long as the supply has approximately 200mA capacity spare, above the Raspberry Pi and accessories requirements. In audio silence the amplifier consumes ~5mA.

The left and right input are each taken through a 100K resistor and then merged together before going through a decoupling capacitor.

A large capacitor has been placed across the power supply, this is so that when the amplifier needs to draw a lot of current for a loud or bassy sound, there is extra power in reserve for a short period of time, to reduce the audio distortion. This also helps when the battery starts to lose it's charge.

The remainder of the circuit has been taken from the datasheet for the LM386 amplifier.

I use the LM386-4 variant of this amplifier, this provides a maximum of 1W output power, which is quite loud for a small speaker.

Two builds of the circuit can be used if stereo output is required. However there are ICs available which can provide stereo output from a single IC and would probably be more appropriate.

The circuit is placed on a small piece of strip board and arranged so that only six tracks need to be cut in a row. There are two connectors. One for the speaker; + and -, the other for power and input signals; left, right, power and ground. The links used in the circuit are all made from the leads cut from the other components.

Project Cost
Item Reference Qty Each Cost
Stripboard 95 x 64mm 37 holes x 24 holes BitsBox 1 £0.85 £0.85
3.5mm Stereo Jack Plug BitsBox 1 £0.42 £0.42
Speaker 8 Ohm 1W eBay 1 £4.00 £4.00
Crimp socket BitsBox 6 £0.09 £0.54
Crimp housing 2 way BitsBox 1 £0.29 £0.29
Crimp housing 4 way BitsBox 1 £0.30 £0.30
Header strip 8 way BitsBox 1 £0.14 £0.14
10nF Polyester film Capacitor BitsBox 2 £0.11 £0.22
100uF Electrolytic Capacitor BitsBox 2 £0.07 £0.14
10uF Electrolytic Capacitor BitsBox 1 £0.07 £0.07
100R Resistor Carbon film 1/4W 5% BitsBox 1 £0.04 £0.04
100K Resistor Carbon film 1/4W 5% BitsBox 2 £0.04 £0.08
LM386N-4 1W Audio Amplifier BitsBox 1 £0.79 £0.79
8-pin DIL socket BitsBox 1 £0.12 £0.12
TOTAL £8.00