Posted on Apr 20, 2012

The circuit uses two gates of a 7400 IC cross-connected to form an astable multivibrator driven by the 1-pulse per second output of the digital clock IC. The hee-haw circuit has a low frequency astable modulator added to make a self-contained European-type siren. Tone and rate can be varied as desired by changing capacitor values.

Click here to download the full size of the above Circuit.

If the tone is too harsh, a simple R-C filter will remove the harmonic content— the multivibrator output is almost a square wave. With the resistor values shown, no startup problems occur; but if the 2.2 k or 2.7 k resistors are changed too much, latch-up can be a problem.

Leave Comment

characters left:

New Circuits



Popular Circuits

Laser Beam Light Activated Remote Control Circuit
Phoenix From Start to End
LEDs or lamps sequencer circuit
hiwatt custom 20 tube amp hum
Infra Red Remote Control
Parallel Computer Bus Description and Pinout
DIY ECG Machine On The Cheap
KTM03 type of circuit for controlling the triac
Combustible gas alarm circuit diagram 7812 7805 555
Alternately flashing lights chain multiple sets of high-power circuit 2