The DS3 provides a precise constant current, isolated stimulus, controllable in pulse duration and amplitude from self-contained batteries. The range of pulse durations available can be varied using a six-position switch and multiplier within the range 20 microseconds to 2 seconds as well as being externally controlled (gated). A three-turn dial on the front panel of the stimulator provides a continuous adjustment of the output amplitude which is indicated on the vernier dial as 0.2 to 3.2. With the four ranges (x10μA; x100μA; x1mA and x10mA), currents from 2μA to 32mA can be selected. The existence of an output pulse is indicated by an LED. The Output is optically isolated from the trigger source ensuring a very low capacitive coupling between trigger source and stimulator to reduce artifacts. The self-contained batteries, without a DC-DC converter, ensure that the stimulator is ultra-quiet and does not induce any high-frequency noise into the recording system.