Amplifier Version 2 - Schematic

This simple amplifier has two channels, each one requiring just two OpAmps, two potentiometers and one resistor. It is a DC voltage amplifier where the lower and upper bound of the input range can be adjusted, for example to -500 mV and +500 mV. It outputs a voltage between GND and VCC (3.3v). Before you build this yourself (it’s not too hard) keep in mind that it will need to be calibrated before its first use and it is also a good idea to put a 10k resistor between each output and the corresponding input pin of your ADC or microcontroller.

Note that this amplifier is supposed to be used with battery power only since it has no filter to remove the usual 50-60 Hz noise band. For the same reason it is also suceptible to simple RFI noise from nearby powerlines. Using it indoors is only recommended when the ADC sampling rate is at or below 1 Hz (one sample per second). It is best suited for use in field locations at some distance from urban electrical noise sources!

Microcontroller and microSD card - Video 1

Microcontroller,microSD card and Amplifier - Video 2

Microcontroller,microSD card and Amplifier - Video 3

Amplifier Version 2 - Calibration

The goal is to calibrate Amplifier Version 2 to have an input range between -500 mV (lower bound) and +1000 mV (upper bound) that will be mapped to the output range between 0V and 3.3V (VCC). We use the names that appear in the schematic at the top of the page. We describe the process for the upper channel (E1). The lower channel (E2) is just the same.

Create a test voltage that matches your desired input lower bound of -500 mV. This can be done with a single battery and a potentiometer as a voltage divider. Set both potentiometers to zero (RP2 slider to the left and RP1 slider to the right). Apply the test voltage to the input (E1). Connect a multimeter to the output (ADC1) and read the voltage. The output voltage should be negative. Slowly increase RP2 (move slider to the right) up to the point where the multimeter reads an output voltage of excatly 0V. You are done with calibrating the input lower bound. Disconnect everything.

Create a test voltage that matches your desired input upper bound of +1000 mV and connect it to the input (E1). Measure the output (ADC1) with the multimeter. It should show a positive value below 3.3V (VCC). Slowly increase RP1 (move slider to the left) up to the point where the output voltage reaches 3.3V. You are done with calibrating the input upper bound.

After you have done this for the lower channel (E2) as well the Amplifier Version 2 will be read for use.