Hey all take a look, i need to design a sound activated alarm sensor using a microphone...this seems like it would do the trick (and it has to use an lm741 btw).

However...if you notice on the right hand side, the microphone trails off (with an indicator arrow) does this mean that i should connect it to ground or VCC?

Also, what do i connect the speaker to? It also has that trailing indicator arrow.

 

The schematic drawing has several errors.

- 0-100V must be 0-100mV instead.
- The 10K resistor at the output of the Opamp has to be connected to the gate of the SCR. An SCR has 3 terminals instead of the two shown:

http://en.wikipedia.org/wiki/Silicon-controlled_rectifier

- One side of the speaker (used as microphone, connected to the + input of the Opamp) is to be connected to the GND.
- One side of the buzzer (A speaker won't work here) should be connected to the +15VDC

The concept seems primitive. It might nevertheless work well though.
- You should consider adding a potentiometer to have a bit of control over the sensitivity.

 

Maybe something like this:

Edit: What he said, except the label is 0-10V

 

There are many things wrong with that circuit.

1) The 741 op amp is a poor choice. This op amp requires a dual power supply. You might be better to use a single supply op amp such as an LM358.

2) Your op amp has no feedback and hence you are using it with open-loop gain which is like 100,000. You should limit the gain to about 300-500.

3) Most miniature microphones are of the electret type. These need to be biased properly with about a 1kΩ pullup resistor.

4) The 1kΩ resistor in series with the SCR does not belong there. This is going to severely limit the current to the Sonalert to the point where it wouldn't work.

5) You need to trigger the GATE of the SCR.

 

He isn't using a microphone. He's using a speaker for a microphone.
Not likely it will ever get to 10 volts, but that's what the sensitivity adjustment is for.

 

Thanks for your assistance everyone, if i wanted to find another similar circuit, what are the key words i can search for?

 

Maybe something like this

Nice editing.

Edit: What he said

What makes you think it's a he ?

http://en.wikipedia.org/wiki/Yoko_Tsuno

except the label is 0-10

Unless I have eyesight problems or a serious drug addiction, I still read 0-100 .

 

Got it. 0-10 volts times 1k/101k = 99mv.

It's a sound activated alarm. That's my first guess at googling.

Edit: Welcome, female person.