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 an iPod or any MP3 player. The “Unplugged” also provides a DSP effects unit which allows the user to choose an audio effect and apply it to a microphone or instrument.

Goals and Objectives• Inputs for microphone, instrument or MP3 player• Power management system must be capable to fully charge

and run off a battery.• Must be portable• User must be able to apply an audio effect to an input and

monitor it by means of a display• User must be able to monitor parameters such as battery

voltage, solar panel voltage and state of charge of the battery

Specs and Requirements• Should weight less than 30 pounds• The system will include a ¼ inch TRS input for a microphone or

instrument level signals and an 1/8 inch input for an iPod or auxiliary audio source.

• Capable of delivering a minimum output of 30 Watts RMS• Capable of operating for at least 3 hours• MP3 input has to be equipped with an EQ circuit with a

dynamic range of +/-6 dB• Incorporate 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

Overall Block Diagram

Audio SubsystemVirtual Ground, Preamplifier, Mixer and Audio Amplifier

Audio Subsystem Overview

Power Distribution• TLE2426 “The Rail Splitter” from TI• Splits input voltage in half• Biases IC’s properly• Consumes only 400 µA from the 9 V LDO

Audio 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

Pre-Amplifier• Voltage Gain of 10• ¼ of LME49740• High-Pass Filter at 72 Hz

Mixer•¼ LME49740

Equalizer• Specs called for an EQ with at least +/- 6 dB of dynamic range• Best Solution: Baxandall Tone Control Circuit

Baxandall Circuit

Fl=320Hz

FH=1.1kHz

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 6 dB at both sides of the band

Filter Frequency Response

• Frequency response with potentiometers fully CW• Maximum Boost of 6 dB at both sides of the band

Audio Amplifier IC• TDA7396 from ST Microelectronics• Class H audio amplifier• 11 lead SIP Package• Operates between 8V and 14.4 Volts• Quiescent Current of 90 mA• 45 W RMS Power with 9V rail

Audio Amplifier Circuit

Power SubsystemBattery, Solar Panel, Battery Charger

Power System Overview

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 Current

Virtual 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)

LM2940T 9V Regulator 7805 5V Regulator

15mA(1)8mA (1)

Miscellaneous 70mA

Total 300mA

Summary of The Current of Different Components

Battery ChosenPower-Sonic 12V/5AH Sealed Lead Acid (AGM) Battery

•Valve regulated allows safe operation in any position•Measures L: 3.54 in W: 2.76 in H: 3.98 in•High Shelf Life (% of nominal capacity at 68°F (20°C))

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

• Weights 3.5lbs

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

KVVinR 100174.2/1

RFB3 || (RFB1THERMISTOR ||RFB2) 3.3V14.4V 3.3V

2||1||32504 RFBTHERMISTORRFBRFBKRFB

Solar Panel Mount

Solar Panel Mount

Enclosure

Enclosure•19” X 5.25 X 12.25”• Aluminum•3.3 lbs

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

Speaker

•Gallien-Krueger 210 BLX•16.5 x 23.5 x 16 inches(W,H,D)•15 inch horn•200W RMS• 30 lbs

DSP and MonitoringSubsytemMicrocontroller, DSP unit and LCD

ATmega 328

• 32KB of flash memory• 1KB EEPROM• 23 digital input/output pins• 16Mhz clock• 5V operating voltage.• Arduino Uno as development board• Programmable in C.

Microcontroller Block Diagram

Atmega 328

• Monitors solar panel voltage.• Monitors battery voltage.• Runs algorithm to determine remaining battery. • Monitors audio effects unit in order to display

the current audio effect. • Interfaces with LCD in order to display these

values.

LCDHD 44780• 2.7 to 5.5V operation • LCD drive power 3.3 to 11V• 4 lines 20 characters each • 240 character fonts• Widely used• Costs about $7• Easily interface with Atmel 328.

HD 44780

• Solar Panel voltage and battery voltage is displayed as well as audio effect.

BTSE-16FX

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

rotary encoder

BTSE-16FX

Monitoring Subsystem

Testing

Testing

• A 1kHz 2mV Pk-Pk sinusoidal wave was applied to the pre-amp and a voltage gain of 10 was confirmed

• A 1kHz 1 V Pk-Pk sinusoid was applied to the audio amplifier input and a gain of 105 dB SPL was confirmed (A jackhammer 1m away is 100 dB SPL)

• The solar panel was connected to the battery

charger for 5 hrs charging the battery by .15V with the load disconnected

• Battery discharged by .3V with load connected and solar panel attached for 5hrs.

Testing (Continued)

• Battery discharged by .4V with load connected with the solar panel charger turned off.

• The LCD values for battery voltage and solar panel voltage were compared to multimeter measurements and they were accurate to the nearest tenth of a volt.

• The grey code encoder was cycled through every possible position and the logic values were compared with a multimeter to make sure that the LCD was displaying the correct effect

Administrative

Timeline

Work DistributionHugo Sandra Gretchen

LCD X

Charger Design X

Audio Circuit Design

X

Microcontroller Coding

X

PCB Design X

PCB Soldering X

Effects Units X X

Enclosure X X X

Power Distribution

X

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 $ 40

Amplifier enclosure $40

4ohm 15 inch speaker Free

PCB $ 150

Faceplate TBD

Total Spent $ 573.54

Original Budget $ 1000

Demo • Original Enclosure

Demo (Cntd) • Original Enclosure

Questions???

UnpluggedA Solar Powered Audio AmplifierWith DSP Effects

Group 16Gretchen RiveraHugo CastellanosSandra Munoz