Hi, I need a way of altering the frequency of a 555 astable multivibrator over a period of about 5 seconds... from around 100hz to 500hz, so some way of changing the divider/timing resistors or capacitor. I need as linear a response as posible for this, but that is not vital. Any ideas? cheers
Circuit here gives a sweep output frequency siren, using a couple of 555s, first one to set the sweep period. Looks like the voltage at Control pin#5 on the second 555 is varied by the charge on the 330uF cap to vary the frequency of the sound oscillator. One to play with, looks fun even if it's no good for you.
http://www.web-ee.com/primers/files/555AN.pdf some good stuff. For a wide range linear up & down sweep I think I'd use a quad opamp, 2 for a triangle-wave generator followed by a variable gain amplifier (like front end of this), use the spare for a unity-gain buffered virtual ground. Feed the wave to a 555 pin#5.
