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Posted by: vivi on October 31, 2009 at 3:03 PM

I haven't built this circuit but I'll try to help.

First, the oscillations are quite slow, so you might need to wait some time before the circuit starts emitting sound. About 70 seconds with the values from the schematic. You can attach an LED+resistor between pin 3 of the 555 and ground to check if this part operates correctly.

Then, if the first part works, remove the 555 and attach the transistors emitters (which were connected to pin 3 of the NE555) to ground. You should hear a high pitched sound. If not, check this part of the circuit. You might also be generating a too high pitched tone to be audible. To check for this, temporarily attach 2 0.1uF capacitors in parallel with C2 and C3. If you hear a tone, this means C2 and C3 are too small and should be replaced by higher values.

I hope this helps.

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http://makezine.com/images/14/evasivediagram.gif is the correct diagram, in the pdf it shows the 9v shorted, between the -side of C1 and the speaker... clipping this wire should fix the problem but be sure the +9v still goes to to the speaker.

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