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This project is a robotic receptionist. I am testing the speaker component, the purpose of which is to give a welcoming voice message to the guests. Most of the time when melody or any type of higher frequency audio signals are concerned, we always take into account the use of piezoelectric low wattage signals with all embedded boards. This time the concern is a little different, the audio signals of human speech frequencies from the arduino board will be obtained and from that, conducting the speaker test experiment will be done.
The background of the experiment relates to the frequency response of different speakers with the power in/out and impedence. Arduino board sends PWM signals which are to be converted into analog signals and then a stage of amplification is required before sending them to the speaker. This is a requirement so that the volume will be sufficiently loud enough to be heard accurately by the guests.
Obtain the best suited speaker in respect of power, frequency and impedence. I want a clear sound, audible without interference or feedback.
Assuming very initially that 8ohm impedence speaker magnetic or piezoelectric will be a good start.
Using ua741 (op-amp) as an audio amplifier.
You have to know the speaker`s resistance so when you are connecting to a new amplifier or any unfamiliar sound system, you don`t risk damaging it. All available data should be taken into account during the testing of a system.
Body of the report
ORCAD 10.1 circuit simulation
SMPS (specification 1.5 to 12 volts)
Multi-meter (Specs: least AC-volt count of 0.001 volts)
The experiment will be done to check the best speaker, which will be used to attach with ARDUINO board. A wav file is played using ARDUINO NANO V3.0; setup consisting of 1 button, which is on a press play specific wav file loaded on SD card. The welcome recording is the wav file.
1- ARDUINO NANO V3.0 2- SD card Module.3- SD card.4- Bread Board.5- One push Button.6- Two 1K resistors.7- Two 10K resistor.8- One 1uf capacitor.9- One 0.05uf capacitor
10- One 250uf capacitor
11- Speaker.12- Wires.
13-LM386 (Audio Amplifier)
Experiment Procedure and circuit schematics
Step 1: Make circuit in ORCAD Capture and make layout. Then make a PCB of the audio Amplifier which is used to provide more current or power to the speaker.
Firstly, assume to use ua741 (op-amp) as an audio amplifier, but I find that it needs more circuitry as compared to LM386 and also signal is low. Since it is called small signal op-amps, LM386 is a low power audio amp.
Step 2: Here the coil speaker is used instead of piezoelectric speaker because the piezoelectric is used to play high frequency voice recording of wav file or we can say it is used only for listening to melody.
Firstly, assume that we are using the piezoelectric speaker with our circuit because it requires less power than other available alternatives and there is no need to add any additional amplifier and it works with the help of only one transistor BC547 or BC548 . However, I do find that the Piezoelectric speaker is only for high frequency voice recordings or we can say it is only for melody playing. Then, I tried using the coil speaker and it shows in my testing that it needs more power as compared to piezoelectric speaker so I added the additional audio amplifier to increase the amplitude of the signal to an adequate volume level.
Step 3: Now connect the speaker to the LM386 Audio Amplifier and the IC take input from ARDUINO board pin no.9. And it further connects to the IN+ (pin3) of the LM386.
Step 4: writing the code in ARDUINO 1.0.3, Algorithm of code setup is shown below.
The assumption of using piezoelectric speaker of same space as magnetic speaker was wrong as piezoelectric speakers are best at high frequency only. This was clearly determined during my testing of the two available speaker options.
RESULT Analysis using simulation software PROTEUS
With the application of 8 ohm speaker the circuit is performing well, the voice recording of the wav file is performing satisfactorily. This has been analyzed using virtual circuit in proteus and a speaker of 8ohm connected to the PC in real time.
The output is analyzed using the CRO connected to the speaker as shown in the above circuit; and by hearing the voice from the speaker connected to the PC. The results are satisfactory in this trial.
RESULT Analysis using simulation software MATLAB
In matlab I have developed the code which will show the frequency response of piezoelectric-speaker and a coil-speaker. Below are the graphs showing the varying frequency response which is obtained from trials of the two different speaker options.
It is clear from the above matlab and proteus analysis that coil-speaker performs more efficiently as compared to piezoelectric-speaker at human voice frequencies, and therefore is a more suitable choice for my purpose as a welcoming component in this robotic receptionist.
Discussion and conclusion
An Arduino UNO board was connected to 8ohm speaker with the help of LM386. The LM386 is a power amplifier designed for use in low voltage consumer applications. The power drain is only 24 milli watts when operating from a 6 volt supply, making the LM386 ideal for battery operation, which is how my robot will be powered. The PWM signal comes from the Arduino UNO board and goes to pin (3) of the LM386 with the help of RC circuit. The audio speech file is saved in SD card with wav extention. Vcc is connected to 5v, the speaker is connected to output pin (5) of the LM386. The circuit is shown in figure 1.
In conclusion, I found out that the orcad circuit for the amplifier and the 8ohm speaker is best suited for the project. The result was found by using simulation software PROTEUS, and simulation software MATLAB as shown in Fig 4, Fig 5, and Fig 6. The next step after doing the experiment test is to start assembly of the parts and finish the completed project.
Please remember that this paper is open-access and other students can use it too.
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