ASTABLE MULTIVIBRATORS -Astable multivibrators are counterparts to oscillators. -They produce pulses at frequencies determined by resistors and capacitors. -They use chip 555, which turns off and on as the output goes high to low between 1/3 and 2/3 Vcc. -The “duty time”, or length comparison between high time of a pulse and total time is not symmetrical unless there is a large difference between the numbers of resistors in and out of the multivibrators.