Hardware - test signal generator

Hardware

DacqUSB

Tracker

Microdrive

Headstage

Signal generator

Software

Tint

fRate

DacqWM

The test signal generator (affectionately known as the “test rat”) produces two low-amplitude (200 µV) sine-wave signals, at 1 kHz and 6 kHz respectively (8 independent outputs are provided at each frequency). This allows headstage buffer amplifiers to be tested for correct functioning and intact wiring. The dual inputs are useful for testing and debugging differential recording setups, where it is necessary to be able to distinguish between the signals arriving at the A and B inputs of the differential amplifier.

The test generator is designed to drive a high impedance headstage amplifier, and to have very small signal levels that simulate the size of neuronal spikes: the 6 kHz output is about 150 µV peak-to-peak, and the 1 kHz output 750 µV peak-to-peak (so that the interference pattern produced in differential recording setups is clearly recognisable as 6 kHz "wobbles" on an underlying 1 kHz wave). It is powered by two 9V (PP3) batteries.

The scope image shows test waveforms on the dacq 10-channel digital oscilloscope -- sweep rate 2 ms/div, amplitudes as shown on the individual Y axes. The generator is used in single unit setups by feeding 1 kHz into the electrode inputs and 6 kHz into the reference inputs. If the wiring is correct, an interference pattern is produced which is like the 3rd and 4th traces on the attached figure. For the 1st and 2nd traces, the 1 kHz electrode inputs have failed (hence only the differential signal is visible). For the bottom four traces, only the electrode signals are visible (6 kHz reference missing).

Click for oscilloscope image