Building a ADSR or LFO with certain features can become very complex and costly. And there are features that can not be realized at all. Like special waveforms. Other functions are hard to realize in the analog domain. So i wanted to experiment with a microprocessor in the digital domain. To start with i build a testboard around the ATMega328p and the 12bit analog to digital converter MCP4921. I added some hardware features that i found might be useful.
Analog inputs: 4Pots 2CV
CV inputs with selectable threshold +2.5V/+5V
Several digital inputs for switches.
Two digital inputs normalized to 5V with overvoltage protection
Analog output with 12bit DAC MCP4921</li>
Analog output switchable 0..5V / 0..10V / -5V..+5V
2 LED for visualizing analog output
External clock 20MHz
External voltage reference