Annoying alarm generator

Thread Starter

kuxz

Joined Oct 11, 2014
4
I would like to create an annoying alarm generator through the use of LM358. I've tried to generate a square wave output using this circuit (http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/square.html) and the output connected to a capacitor before going to a 8ohm, 0.25W speaker. However, I am only able to hear a monotone output. Do I need a audio amplifier circuit?

However, I am only limited to a few analog components for my project which includes:
LM358
BJT
MOSFET
resistor
Capacitor
Diode

Desired annoying alarm tone link:
 

Thread Starter

kuxz

Joined Oct 11, 2014
4
This is the current circuit that I've built and the 8ohm, 0.25W speaker is connected after the 1uF capacitor. The duty cycle of the output can be controlled through tuning the potentiometer R1 and R4. The problem is that even though I am able to control the duty cycle of the output, the sound generated from the speaker remains to be monotone. Do I need to modulate the frequency in order to generate the tone?

Circuit.JPG

Waveform.JPG
 

Brownout

Joined Jan 10, 2012
2,390
I don't understand. You say you have a monotone generator, but you wan to generate the tone. You're gonna need to describe what the tone is.
 

DickCappels

Joined Aug 21, 2008
5,952
By listening to your example, it is clear that two oscillators are in use. One to make the tone and the other to vary the frequency as a function of time. Back in the 1960's we did this with a couple of neon lamps and a few resistors and capacitors. Now it needs integrated circuits?)

I have tried two different browsers. I can see your simulator output but I cannot see your schematic. Please try again.

@Brownout You can hear the tone by playing the YouTube clip.
 

Brownout

Joined Jan 10, 2012
2,390
@Brownout You can hear the tone by playing the YouTube clip.
Thanks, I don't do videos (for several different reasons) but I have the idea form your description. Here is a circuit that does it:

http://www.circuittrue.com/make-simple-flasher-with-beeper-circuit-for-turn-indicator-switch-in-motorcycle/alarm-schematics-alarm-circuits-it-uses-two-555-timers-in-the-circuit-the-555-on-the-right-is-wired-as-an-alarm-tone-generator/

If the Ts wants an explanation, there are several here that can do that.
 

Dodgydave

Joined Jun 22, 2012
8,476
Your missing a 100K resistor from pin 3 to pin 4 ground, the first op amp is a sawtooth generator and needs a half rail supply on pin 3.
 

ian field

Joined Oct 27, 2012
6,539
Thanks, I don't do videos (for several different reasons) but I have the idea form your description. Here is a circuit that does it:

http://www.circuittrue.com/make-simple-flasher-with-beeper-circuit-for-turn-indicator-switch-in-motorcycle/alarm-schematics-alarm-circuits-it-uses-two-555-timers-in-the-circuit-the-555-on-the-right-is-wired-as-an-alarm-tone-generator/

If the Ts wants an explanation, there are several here that can do that.
Apparently there is a commercial product called an Annoyatron that would save a lot of experimenting and construction.
 

DickCappels

Joined Aug 21, 2008
5,952
Ditto see post #8.......
<<== Take note, you really need that resistor. I can't see how the circuit would even work in the simulator without that 100k resistor.

@Brownout, the TS is looking for a continuously varying tone rather than the bi-frequency British siren. Do you have one ready to go that drives the NE555 control voltage input with a repeating function (e.g. sawtooth, sine, etc.)?
 

WBahn

Joined Mar 31, 2012
24,854
Apparently there is a commercial product called an Annoyatron that would save a lot of experimenting and construction.
Yep, why waste time on experimenting and construction when solving a homework problem. Much better to just use a commercial product. Should the grade be based on how expensive the product is, or on how cheap?
 
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