Patches: 1) Swap U1 Vin/Vout -- 3 cuts + 3 wires Notes: 1) U1 Vin/Vout pins are swapped 2) Add a reset circuit Use a SNLVC2G06 (dual open collector inverter): At VCC = 5V: VIH = .7 * VCC = 3.5V VIL = .3 * VCC = 1.5V VOL = .55V IOL = 32mA Assuming that the capacitor is clamped to VOL most of the time, the R*C that corresponds to charging from VOL to VIH in T seconds: The basic capacitor charging equation: V(t) = VOL + (VCC - VOL) * (1 - e(-t/R*C)) (1) Replacing V(t) with VIH and T: VIH = VOL + (VCC - VOL) * (1 - e(-T/R*C)) (2) Solving for RC: (VIH - VOL)/(VCC - VOL) = 1 - e(-T/R*C)) (3) e(-T/R*C) = 1 - (VIH - VOL)/(VCC - VOL) (4) -T/R*C = ln(1 - (VIH - VOL)/(VCC - VOL)) (5) R*C = -T/ln(1 - (VIH - VOL)/(VCC - VOL)) (6) Substituting in for T=1ms, VIH, VOL, and VCC: R*C = -.001/ln(1 - (3.5 - .55)/(5 - .55)) (7) R*C = -.001/-1.08744 R*C = .009196 (8) Setting C = .1uF R = .009196 / .0000001 = 9196 Using an R near 10K should do the trick: The maximum discharge current is IOL. Use Ohm's law to determine determine discharge resistor: V = I * R R = V / I = 5 / .032 = 156.25 Setting Rdischarge = 180 should be good enough. The charge/discharge ratio is: Rcharge/Rdischarge = 10K/180 = 55.5