Operating Instructions First, connect the PCB to a 20 -24 V unipolar power supplying, using the terminal block labelled power in Fig. . Then select measurement settings within the firmware and flash the microcontroller. We recommend sticking to the default sample rate of 200 kHz and the default modulation frequency of ~410 Hz, but if necessary these can be changed by modifying the values of Fsig and Fsample in the pre-processor definitions of the file "LockInFirmware.ino". The relevant locations are clearly commented.