Voltage controlled envelope generator

I did build this circuit arround an up-down integrator made from a half LM3900. The logic produces signals for each phase of the envelope, these can be made visible with LEDs, and can act to trigger various events, i.e. delayed vibrato.

Operation overview: When the gate goes high the flipflop inside the 555 sets, the output is the attack signal which switches the attack CV to the exponentiator and the current from the exponentiator to the "up" input of the 3900-integrator. When the output of the integrator reaches 10V the 555 resets and "attack" goes low. The decay signal is asserted when gate input is high, and attack is low, and the output is higher than the sustain level. The current is now switched to the "down" input of the 3900. The output now decays until the output is less than the sustain CV. Then both switches to the 3900 are open and the integrator goes to a hold mode. (The logic signal for this part can be simply derived from the others.) Finally when the gate goes low, the circuit goes to the sustain mode, which is like decay mode, but switched to a different input. The supply bypassing is not shown, use a 4.7uF cap across the 555s power rails. The supplies of the other logic ICs should be decoupled with 100nF each. Also one should add adders for more inputs. The schematic is not 100% ready. Although I will give it a redesign, eliminating the need for the negative supply (and using up the spare amp of the 3900) , the circuit is fully functioning.