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.

VIDEO 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 Reference: LM386 Raspberry Pi OS Images

Circuit for Amplifier
Circuit 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. Build 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