Check out this interesting wideband AC millivoltmeter circuit from 1990. The simple design features 12 ranges, decent accuracy, 200 µV accuracy, and a frequency range from 20 Hz to more than 2 MHz.

The below circuit diagram uses Arduino UNO R4 WiFi as a main controller, but you can use any other microcontroller by swapping it and making little modifications to the code. Here I decided to use ...