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Topic: Electret microphone doesnt seem to work. (Read 377 times) previous topic - next topic

saos

Oct 09, 2018, 09:02 am Last Edit: Oct 09, 2018, 09:24 am by saos
Hello , i am working on my final semester project. I have made a circuit on a breadboard that uses a mic to detect sound and light up leds. However when i finished the circuit , sound doesnt seem to get detected by the mic and the leds doesnt even lit up. When i inserted power to the breadboard the leds are lit up for a split second upon inserting the pins to breadboard. Is my electret mic faulty?

Here is the schematic.

Paul__B

Is my electret mic faulty?
No, but it generates only a few millivolts and you require a lot of millivolts to switch that first transistor.

Nice schematic.

DVDdoug

Quote
Hello , i am working on my final semester project.
In electronics???    

Check the DC output (collector) of Q1.  The circuit might work if you adjust the bias on the transistor (by adjusting R2).

If you have an oscilloscope at school you can do some AC/signal measurements to find out if you need more amplification or louder sound.  

Of course, your audio signal is AC so at best your LEDs will only be on half of the time so you won't get "full brightness".   In reality, they will be on less than half the time.

jremington

#3
Oct 09, 2018, 05:33 pm Last Edit: Oct 09, 2018, 05:45 pm by jremington
Too little gain and the second stage bias is way too low. Here is a simulation of the circuit using LTSpice, suggesting that the LED current is about 3 uA maximum.


saos

#4
Oct 09, 2018, 06:02 pm Last Edit: Oct 09, 2018, 06:03 pm by saos
im sorry im a complete beginner on this , i have followed many tutorials that uses this same schematic except that they used a 9mm instead of a 6mm microphone that i used.In their videos , the circuit seems to be working fine. I have also make sure that i connected the components properly and in the end they dont produce the same results as in the tutorials.

jremington

#5
Oct 09, 2018, 06:07 pm Last Edit: Oct 09, 2018, 06:08 pm by jremington
Quote
im sorry im a complete beginner on this
And this is your final semester project?  Having taught analog electronics design, I would fail this project.

At some point, you will hopefully learn to pay attention in class. Or do you attend class at all?

saos

#6
Oct 09, 2018, 06:26 pm Last Edit: Oct 09, 2018, 06:31 pm by saos
I took computer science and this is my first sem , as far as what i've learned in class i wasnt taught on what are the transistors , resistors , capacitors do or even how to use the breadboard. I dont even know why i got this project on my first sem. But im also trying to learn about these. Anyways thank you for the help everyone.

DVDdoug

#7
Oct 09, 2018, 08:03 pm Last Edit: Oct 09, 2018, 08:22 pm by DVDdoug
Quote
I took computer science and this is my first sem , as far as what i've learned in class i wasnt taught on what are the transistors , resistors , capacitors do or even how to use the breadboard. I dont even know why i got this project on my first sem.
I don't know where "they" got it either, and I don't know why you'd be doing an electronics project after studying computer science (which should be mostly software).

I misunderstood you.  I thought this was your final semester  in college.    But, now I understand it's the final project  for this  semester.



This is the Arduino  General Electronics forum so if you want to do something similar in software (with the Arduino) take a look at this.   It was really designed to work with hard-wired line-level audio signals (about 1V) but it  also works with the SparkFun Microphone Board (which has a built-in preamp).     

...With the SparkFun board, I had to turn-up my TV louder than I normally listen to get "good blinking".  At normal sound levels it was just blinking randomly.  I could probably get better results by tweaking the noise threshold but I didn't bother since it wasn't intended to be used with a microphone.

Quote
i have followed many tutorials that uses this same schematic except that they used a 9mm instead of a 6mm microphone that i used.In their videos …
A larger microphone might be more sensitive and it might not.   The transistors have quite a bit of tolerance (variation) too and because of that it probably should have a pot (potentiometer = variable resistor) to adjust the bias.  And of course, the signal level depends on loudness.*    I'm not going to say it can't work... maybe with louder sound and/or a resistor change... but it's a screwy circuit...      It's particularly strange to identically-drive 4 LEDs with 4 transistors instead of driving them all with one transistor (with separate current-limiting resistors for each LED).



* Almost everything with a microphone has a sensitivity control or volume/level control because sound levels very a LOT.  ...A lot more than you may realize since our ears are (approximately) logarithmic.   I don't know if this thing is supposed to work with a live rock band or with normal conversation.

P.S.
If you want to continue with this - R1 may be too high.   Check the microphone specs.    Typically, I see 2K being used with electret mics.  The voltage across the microphone should be between about 2V and about 4.5V (half of 9V).   (Higher resistance will give you less voltage across the mic.)


jremington

#8
Oct 09, 2018, 11:31 pm Last Edit: Oct 10, 2018, 12:26 am by jremington
Quote
I dont even know why i got this project on my first sem.
This is a terrible project for computer science, as it has nothing at all to do with computer science.

Complain to your instructors.

MarkT

Hello , i am working on my final semester project. I have made a circuit on a breadboard that uses a mic to detect sound and light up leds. However when i finished the circuit , sound doesnt seem to get detected by the mic and the leds doesnt even lit up. When i inserted power to the breadboard the leds are lit up for a split second upon inserting the pins to breadboard. Is my electret mic faulty?

Here is the schematic.

Various problems with that circuit at a glance - completely unstable biasing for the first transistor and not enough gain. 

Try moving the top of R2 to the collector of Q1, not the 9V rail, then it might bias sensibly - currently its
probably nearly saturated and unable to do anything.

Why 4 transistors to drive the LEDs in parallel?  If the LEDs are red just put them in series and use one transistor to drive the whole string.

You'd get much more stable and predictable behaviour using opamps and comparators I reckon.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

saos

Hey everyone,  thank you for trying to help even though i know nothing about circuitry. I tried changing my circuit diagram and it finally works. Looking forward to learn about this more and do more projects!.

polymorph

How did you change it? Did you change it as MarkT suggested, or in some other way?
Steve Greenfield AE7HD
Drawing Schematics: tinyurl.com/23mo9pf - tinyurl.com/o97ysyx - https://tinyurl.com/Technote8
Multitasking: forum.arduino.cc/index.php?topic=223286.0
gammon.com.au/blink - gammon.com.au/serial - gammon.com.au/interrupts

saos

i used a 4k7 resistor to connect to the mic and used a 1uf capacitor instead of a 0.1uf. Then i followed the advice to put the leds in a series using one transistor.After that i used a 47uf to connect to the negative and positive power line.

ChrisTenone

i used a 4k7 resistor to connect to the mic and used a 1uf capacitor instead of a 0.1uf. Then i followed the advice to put the leds in a series using one transistor.After that i used a 47uf to connect to the negative and positive power line.
Can you show a schematic of the working circuit?
Atmosphere carries combustion vapors to places where they will do good instead of harm - Mike Faraday's 'History of a Candle': https://www.youtube.com/watch?v=6W0MHZ4jb4A

Whoops ::)

saos


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