Envelope generator

A digital envelope generator for an analogue synthesiser

This project is an attack-sustain-decay-release (ADSR) envelope generator for an analogue synthesiser. The circuit is based on an ATtiny85 microcontroller.

Description

There's not much to say really. The four control potentiometers are connected between 5v and ground. The wiper of each is connected to an analogue input on the AtTiny.

The gate input might be 12v or more, so it is connected via a 10k resistor to the base of an NPN transistor whose collector goes to a pin of the AtTiny.

The PWM output from the AtTiny goes via a low-pass filter (10k/47n) to an op-amp in non-inverting configuration. The feedback gives an adjustable gain so you can tweak the output level to match your VCO or VCF "standard" levels.

Analogue power comes from the synthesizer's 15-0-15 power supply. The logic supply is regulated using a 5v linear. I used a 78L05

Source code for the ATtiny85

• gitlab
• github

If you want to clone the repository, go up a level.

Circuit diagram

Click image for a larger version.

The round-tuit department

The project might fit into an AtTiny13 with a few tweaks to the software. It might make the module a bit cheaper to build.