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electronic wireless drum-kit |
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- page last modified, March
2013- (página en
castellano)
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| a
simple and nice working envelope follower |
| The
picture shows a PCB with two
envelope filters (followers) incorporated. The PCB is designed as
satellite to be connected on a base circuit look
here. Using SMD (surface mounted devices) allows to build a electronic circuit very small that allows, on the other hand, to use of all possible analog inputs of the base-circuit. |
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| The circuit is
quite straight forward. Using a rail to rail single opa336 with the positive input, pin 3, connected to GND, the op-amp amplifies only the positive part of the incoming signal. As the goal is to get the envelope of the signal (a variable DC signal) only one diode, a 1N4148, is used to forward the positive signal achieved from the piezo-transducer. The voltage charges C3 and discharged through R3. The time constant is with 56k and 470nF aprox. 25ms. Increasing the values of R3 and C3 increases the decay time. As I use the circuit to trigger a self made PAD I use a small discharge time of 25ms . As we are not interested in signals above 1000Hz the feedback (R1, 100k) of the op-amp is in parallel with a small capacitor of 2,2nF. The cutoff frequency is about 720Hz. To improve the sensitivity a Schottky diode can be replacing the 1N4148. For my use I connected a 56k resistance in serial with C1 to dump the amplification. |
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