UnpluggedA Solar Powered Audio AmplifierWith DSP Effects

Group 16Gretchen RiveraHugo CastellanosSandra Munoz

Project Description

The “unplugged” sound system is a solar powered audio amplifier that provides the freedom to play music anywhere without having to be attached to the power grid. It provides inputs for not only musical instruments, but also for microphones and an iPod or MP3 player. The “Unplugged” also provides a DSP effects unit which allows the user to choose an audio effect and a respective input to apply the effect to.

Goals and Objectives• Power management system must be capable to fully charge

and run off a battery.• User must be able to pick which of the effects to apply and

which analog input to apply them to.• Inputs for microphone, instrument and line signal• User must be able to continuously monitor parameters such as

battery voltage, solar panel voltage and current by the means of a display.

• Must be portable

Specs and Requirements• Should weight less than 30 pounds• Capable of delivering a minimum output of 30 Watts RMS• Capable of operating for 90 minutes• Each analog input has to be equipped with an EQ circuit with a

dynamic range of +/-10 dB• To incorporate three DSP audio effects including reverb• The system must be able to run off a 12V battery• The battery must be charged solely by a 20W solar panel• The system will include 1 microphone input for low impedance

microphones, one ¼ inch instrument input and an RCA input for auxiliary audio sources

Overall Block Diagram

Audio SubsystemPreamplifier, Equalization, Mixer and Audio Amplifier

Audio Subsystem Overview

Virtual Ground• TLE2426 “The Rail Splitter” from TI• Splits input voltage in half• Provides virtual ground so op-amps can be biased• Consumes only 400 µA from the 9 V LDO

Testing Equipment• LM386 Audio Amplifier 4 Ohm RCA Speaker

• ONLY TO TEST FUNCTIONALITY• Rigorous electrical testing will be conducted eventually• DC offset, RF Noise, Frequency Response

Preamplifier IC

SSM2019 from Analog Devices• 8 lead Plastic Dual-in-line-package (PDIP)• Wide range power supply: 4V-18V• Will be operating at 9V with virtual ground • Low Quiescent Current: 4.6 mA• Voltage gain of up to 3500• Excellent noise figure @ 0.2 µV between 20 Hz – 20 kHz• ONLY ONE EXTERNAL COMPONENT

SSM2019 Implementation

Equalizer• Specs called for an EQ with at least +/- 10 dB of dynamic range• Best Solution: Baxandall Tone Control Circuit

Equalizer IC• LME 49740 from National Semiconductor

• Quad high performance, high fidelity audio operational amplifier• 14 lead DIP Package• Wide supply voltage: 4V to 17 V• Quiescent current of 20 mA for all 4 amplifiers• Excellent noise figure: 0.4 uV in the full audio range• Unity Gain Stable

• Design Specific Considerations• FL=300 Hz, FH= 1kHz• 2 Amplifiers for EQ, 2 for line level signal mixing

Baxandall Circuit

Fc=500Hz

Filter Frequency Response

• Frequency response with potentiometers at the center position

• Maximum deviation of 0.191 dB due to virtual ground

Filter Frequency Response

• Frequency Response with potentiometers fully CCW• Maximum Cut of 12 dB at both sides of the band

Filter Frequency Response

• Frequency response with potentiometers fully CW• Maximum Boost of 12 dB at both sides of the band

Equalizer Implementation

Problems • Noise• Breadboard

Capacitance

Solutions• Use Vero board• Use more accurate

components

Audio Amplifier IC• TDA1562Q from NXP Semiconductor• 70 Watt Hybrid class H audio amplifier• 17 lead SIP Package• Operates between 8V and 14.4 Volts• Quiescent Current of 90 mA• 50 W RMS Power with 9V rail

Power SubsystemBattery, Solar Panel, Battery Charger

Battery

9VRegulator

Audio SystemVoltage

Divider

LCD Microcontroller

Battery Charger

Power System Overview

Solar Panel

DSP Effects

Type Pros Cons

Lead-Acid Cheap price, stable at high temperatures, have multiple cycles

Low energy density, cannot be completely discharged

Nickel-Metal Hydride

Better cycle life than lead acid, creates no memory

High self-discharge 20% per month, circuit protection

Lithium-ion Highest energy density, light-weight, faster charge times

Most expensive, circuit protection

Batteries

Components CurrentVirtual Ground TLE2426 400μA (1)Preamplifier SSm2019 4.6mA (2)LME 49740 Equalizer 20mA (1)LME 49720 10mA (1)Amplifier TDA1562Q 90mA (1)LCD 300μA (1)Microcontroller 500μA (1)DSP Effects 100mA (1)BAXXBC0WT 9V Regulator 9

130μA (1)

Miscellaneous 70mA Total 300mA

Summary of The Current of Different Components

Battery ChosenPower-Sonic 12V/7 AH Sealed Lead Acid (AGM) Battery

• Valve regulated allows safe operation in any position• Measures L: 5.95 in W: 2.56 in H: 3.70 in• High Shelf Life (% of nominal capacity at 68°F (20°C))

1 Month 97% 3 Months 91% 6 Months 83%

• Weights 4.8 lbs

Solar PanelsType Pros Cons

Monocrystalline Silicon

Max efficiency 22.7%, produce voltage even at low lights conditions

Most expensive

Polycrystalline Silicon

Cheaper than monocrystalline

Not able to charge when weather is cloudy

Amorphous Silicon Least expensive, can continue to charge at cloudy conditions

Lowest efficiency 5-7 %, short lifetime

Solar Panel Chosen

20 Watt Solar Panel DC 12V Monocrystalline PV Module by HQRP

• Open Circuit Voltage (Voc): 21.6V•    Short Circuit Current (Isc): 1.3A•    Maximum Power Voltage (Vmp): 17.2V• Maximum Power Current (Imp): 1.17A• Dimensions: 420x420x25 mm

IV Curve of Solar Panel

Battery Charging Circuit

Buck configurationDC/DC converter

Battery Charger Prototype

Enclosure Considerations

Yamaha BR 15 Speaker• 19.1” X 25.8” X 14.4” (W,H,D)• 15 inch horn• 200W RMS• 30 lbs

Crown CE1000 • 19” X 5.25 X 12.25”• Rugged Steel• 5.3 lbs

Enclosure Considerations

SKB 4 unit rack case• 22.50” X 9.5” X 21.50”• 12 Lbs

Enclosure Concept• Amplifier enclosure mounted inside SKB case

Enclosure Concept

DSP and MonitoringSubsytemMicrocontroller, DSP unit and LCD

Arduino Mega 2560

• Preassembled with ATmega2560• 256KB of flash memory• 4KB EEPROM• 54 digital input/output pins• 16Mhz clock• 5V operating voltage.• Programmable in C.

Microcontroller Block Diagram

Arduino Mega2560

• Will monitor solar panel voltage and current.• Will also monitor battery voltage.• Will interface with LCD in order to display these

values• Will run a charger state machine with four states,

on, off, bulk and float which will help determine what the state of the charger should be.

Arduino Mega2560

LCD

HD 44780• 2.7 to 5.5V operation • LCD drive power 3.3 to

11V• Provides a choice of size• 240 character fonts• Widely used• Costs about $7

Nokia 3310

• 2.7-3.3V operation• Graphical LCD• 48 row, 85 column

output• 40X38 mm size• Not readily available• Costs about $6.

HD 44780

• Availability• Widely used in previous projects• Did not need graphical functionality• 20X4 provided enough space• Easily interface with Arduino Mega.

HD44780

HD 44780

• Solar Panel voltage and current will be displayed as well as battery voltage.

ADAU1702 issues

• Reverb comes standard on library but chip does not support it.

• The ADAU14x family supports reverb• Development board is about $400.• Would not meet budget or specs.

BTSE-16FX Effects Module

• Provides 16 different digital audio effects• 5V power supply• 64 X 35 mm in size• Costs about $16 dolars.• Effects will be controlled using a 4 bit grey code

rotary encoder

BTSE-16FX

Possible Problems• PCB Design

• Eagle is inadequate for our needs• 100 mm x 80 mm is too small!• Not sure how to transfer programmed ATmega to final PCB.

• Heat Dissipation• Forced air- extra power consumption

Administrative

BudgetItem Price

Solar Panel $ 108.95

Arduino Mega $ 59.65

Battery $ 21.60

IC’s $ 44.63

DSP FX $ 15.00

LCD $ 7.00

Heatsinks $ 9.00

Capacitors $ 12.38

Breadboards $ 35.80

Potentiometers $ 29.53

Perforated board Free

Mis. Audio Connectors $ 10

Amplifier enclosure Free

4ohm 15 inch speaker Free

PCB $ 100

Faceplate TBD

Total Spent $ 442

Original Budget $ 1000

Progress

Research (95%)

Design (95%)

Parts (90%)

Prototyping (60%)

Testing (60%)

PCB (10%)

Overall (60%)

0 10 20 30 40 50 60 70 80 90 100

Questions???

UnpluggedA Solar Powered Audio AmplifierWith DSP Effects

Group 16Gretchen RiveraHugo CastellanosSandra Munoz