This featherwing provides a high-impedance gain stage and a simple envelope follower for piezo contact microphones.
The piezo is connected via a standard 3.5mm TRS shielded audio connector with the following pinout:
- Tip: piezo signal
- Ring: piezo ground
- Sleeve: cable shield (not connected on piezo end)
The board requires a bipolar +12V/-12V power supply, provided via a 4pos Molex SL connector with the following pinout:
- 1: +12V
- 2: GND
- 3: -12V
- 4: signal out (default to unattenuated envelope follower signal).
Jumpers and plated holes are provided to configure which signals are sent to which pins.
- By default, the SL connector gets the unattenuated envelope follower signal.
- By default, no analog pins on the feather headers are connected. Use wire jumpers to connect signals to the analog pins you want to use.
- Jumpers can configure the amplifier stage gain, as well as the envelope follower decay time. By default, the gain is 100x and the decay is set with a 270k resistor.