Wiring Material

This circuit produces a waveform that decays exponentially from a set voltage to near-zero, and then rapidly resets to restart the cycle.
Initially C1 is charged to +12V, and O1, O2 are both off. The timing capacitor there discharges slowly through Rl, the exponentially decay- ing voltage appearing at low impedance at the output of unity-gain buffer RC2. R2 prevents the leakage current from O1 affecting the discharge as D1 is reverse-biased. When the voltage on Cl reaches a value just above zero that is set by R3, R4, the open collector O/P of lC‘l goes low, turning on O1 and rapidly recharging Cl. lCi ofcourse reverts to its original state almost at once, but the recharge mode is prolonged for several mil|i·  seconds by the positive feedback loop through R5, C2 and O2, to ensure Cl charges fully. After this time C2 is also fully charged, and O2 turns off, turning off Ql, and allowing the slow discharge of C1 to begin again. With the component values shown each cycle lasts about ten seconds.