Here are some circuits to help protect your precious microcontroller’s inputs.

Protecting microcontroller analog inputs

Using Mutable Instruments’ Grids as our first example

• You will need a rail to rail op amp. A popular choice would be an MCP6002 chip.
• The op amp would be powered by 5v and ground (not +-12V!). This will “clamp” the cv signal.
• The output of the op amp connects to an analog input of a microcontroller.
• You would need a negative reference voltage source. Grids used a Zener diode. VEE is -12v.
• I usually use a 7905 -5v negative voltage regulator for the reference voltage.
• This is an inverting op amp circuit, you would need to adjust your code to accept inverted values

Adding an input amplitude knob

Adding an input amplitude knob to the Grids circuit would help us accept a wide range of signals in combination with the offset knob. 0-5v, 0-10v, and +-5v.

Protecting microcontroller digital inputs

• It uses an NPN transistor with a pullup resistor
• Note that the Arduino pin will be low when the gate is high, code with this in mind.
• It connects directly to a digital input pin of the Arduino
• To protect your inputs more, you could add clamping diodes to the base of the transistor like below
• The bat42 Schottky diode is commonly used for this purpose

Disclaimer: The information provided in this blog is based on my personal experience and knowledge. I am not formally educated in electronics design, and any design or information should be undertaken at your own risk. It is always recommended to consult with a qualified professional or conduct thorough research before attempting any electronics project. I do not guarantee the accuracy, completeness, or reliability of the information presented on this blog. By using this blog, you agree that I shall not be held responsible for any damages or losses that may arise from your use of the information provided.