Timing/Waveshaping Circuits

Thread Starter


Joined Feb 2, 2010
1)Construct a pulse stretcher using a 74221 one-shot. Select appropriate components to make the pulse width approximately 0.5 s.

74221 PDF

2)Design a variable duty-cycle wave generator using a 555 timer. The output frequency should be 10 kHz and the duty cycle should vary from 15% - 85%. Use a 10 turn, 10 kohm potentiometer to control the duty cycle. The diode in the modified astable multivibrator circuit below theoretically allows the Rb resistance to be shorted out during the charge cycle. The new equations for this circuit will be:

tL = 0.75 Rb C
tH = 0.75 Ra C



Joined Apr 20, 2004
There are data sheets for both devices. Use the part number in Google to find them. Both will have the information you need.