DS4 - Computer Controlled

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The DS4 has been developed to meet the needs of laboratory scientists who require a stimulus isolator that can output a
bi-phasic isolated constant current stimulus in response to an external command voltage signal, provided by a computer
DAC via software. Such a requirement is already met by our NeuroLog System in the form of the NL512 Biphasic Buffer
and NL800A Stimulus Isolators, but the DS4 provides our first standalone device to meet this need.

The DS4 accepts a variety of voltage input ranges (±1V, ±2.5V, ±5V and ±10V) and produces a constant current stimulus output in 4 overlapping ranges (±10μA, ±100μA, ±1mA and ±10mA) from a compliance voltage of ±48V. In addition, the DS4 has a GATE input which allows multiple DS4's to be connected to a single analogue voltage source, with each DS4 being digitally enabled, separately.

One of the problems with stimulators that make use of an external voltage source to define a stimulus waveform is that
small offsets or noisy baseline signals from the DAC's used to drive them can result in unwanted battery drain or perhaps
worse, low amplitude stimulation. The DS4 uses a special "inactivity sensor" to monitor the input voltage and disable the
DS4 output if this voltage falls within 0±0.2% of the full scale value for a user selectable time period of 100ms, 200ms, 1s
or 2s. Unlike other devices which only produce an output when the input voltage exceeds a threshold value, this "inactivity
sensor" reduces battery usage and damaging "leak currents" during infrequent stimulation, while at the same time
maintaining low levels of zero crossing distortion for repetitive waveforms.

The DS4 uses an external power supply to power the input control circuitry and readily available/inexpensive batteries to
provide the opto-isolated stimulus voltage source.

Output: Bi-phasic constant current proportional to the input voltage

Output Ranges: ±10μA; ±100μA; ±1mA; ±10mA for a full scale input

Output Duration: >2μs

Compliance: ±48V from 8x GP23A batteries

Linearity: ±3% of full scale output for each output range

Output Impedance: >900Mohms

Output Rise Time: <5μs (1kohm load), <40μs (1Mohm load)

Frequency Response: Expected DS4 output is maintained for frequencies up to 5kHz.

Inputs:

IN: Ranges: ±1; ±2.5; ±5; ±10 V full scale (selected by an internal jumper) with a limit of ±12V max. without damage.

Input Impedance: 1Mohm

GATE: Range: TTL; Gate OFF if Low; Gate ON if High or open circuit. Limit of ±15V max.

Input Impedance: 10kohm

Inactivity Sensor: The output is disabled if the voltage input remains within 0±0.2% of the full scale value for a user selectable period of 100ms, 200ms, 1s or 2s. This time period can be adjusted with an internal jumper.

Connections: Output - 2mm shrouded, touch-proof sockets (red and black) spaced at 0.75"

Input - Front panel BNC socket

Gate - Front panel BNC socket

Battery Test - Six 2mm sockets

Power - Socket for external power supply

Controls: Gate - On/Off toggle (Off overides BNC input)

Output Range - 4 position rotary switch

Power - On/Off toggle switch

Indicators: Power ON LED Green (lit when the power supply is connected and DS4 is switched On)

Gate Enabled LED Amber (lit when Gate is On and the Gate Input is held TTL high)

Phase +ve LED Amber (lit when input exceeds +0.2% of full scale voltage)

Phase -ve LED Amber (lit when input exceeds -0.2% of full scale voltage)

Power: Included external power supply (input voltage 110V - 220V) providing ±15V DC output. 10 x 12V GP23A Batteries.

Mounting: One or two stimulators may be mounted in a 19" rack using a specially fabricated frame (model D121-11).

Dimensions: 190 x 110 x 80 (w x h x d)

Weight: 500g (approx.)

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