Development History

The D188 Remote Electrode Selector was originally developed for Dr Christopher Brown, formerly of Cambridge University, but now a senior lecturer in the Department of Psychology at Liverpool University.  As part of his research into complex regional pain syndrome, Chris was particularly interested in sequentially or randomly directing the output from a single Digitimer DS7A stimulator to individual fingers via standard digital ring electrodes.

Using Matlab software to control the digital outputs of an inexpensive Labjack DAQ device, the D188 could respond to TTL high/low levels to switch between the 8 channels.  Use of the D188 meant Chris only needed one stimulator to stimulate one of eight fingers.

D189 for Low Voltage/Current Applications

As the relays we use in the D188 are not specified for low currents/voltages, the D189 was introduced specifically for users of our lower current/voltage non-human research stimulators, including the DS2A, DS3 or DS4.  Importantly, unlike the D188, the D189 does not include safety features that are in place to protect the subject during use.

D187 Introduces Individual Control of Each Output Socket

One obvious limitation that the D188 and D189 share, is that they can only switch between 8 discrete pairs of outputs, so it wasn’t long before our customers started asking for an electrode selector with more arbitrary control of the output state and polarity.  The first step in any product development process is the selection of a product identifier and as Digitimer had already used “D190” for our earlier foray into the transcranial magnetic stimulation field, we opted to designate this new advanced remote electrode selector the “D187”.  Once a name was chosen, development could begin in earnest!

The new D187 Advanced Remote Electrode Selector is visually familiar to users of the D188 or D189, but in contrast to these units, it features bi-colour LEDs associated with each output, is powered via its USB socket and is supplied with a dedicated Windows compatioble GUI.  The D187 is currently undergoing global prototype testing at a number of laboratories, but having received excellent feedback from all our evaluators, we are already accepting orders for it.

Choosing the right Remote Electrode Selector

The simplest way to narrow down your options, is to consider the voltage/current you will require.  The D189 employs a specific type of mechanical relay which is suited to low current/voltage applications, so if you need an electrode selector for a stimulator that outputs no more than 100V/50mA and you are conducting non-human research, then the D189 will be your best choice.

For applications that require higher current or voltage and safety for a human subject, you need to choose between the new D187 and D188.  As both are appropriate for up to 400V or 1A (for brief pulses of up to 2ms), they can both be used with our DS5, DS7A, DS7AH, DS7R and DS8R stimulators.  Although all three electrode selectors switch within a few milliseconds, the switching times for the D188 are a little faster than the D187, however, the ability to configure each of the 16 outputs as a Cathode, Anode or Disconnected makes the D187 far more versatile.  For instance, you can incorporate the D187 into a grid electrode arrangement and stimulate at any point within the grid.  If 8 discrete pairs of electrodes are all you need, then both the D188 and D187 would be options.

Software or Digital Control

For the D188 and D189, precisely timed remote control is possible through the use of TTL compatible digital lines from your data acquisition system. One to one control requires eight digital inputs, but the D188/D189 Remote Electrode Selectors can also operate in a multiplexed mode where only four digital inputs are required.

Alternatively, a USB connection to the host computer allows software control of the D188/D189 via a DLL-based API, which can be accessed using your preferred software (C, C++, Visual Basic, C# etc). The D188 and D189 are recognized and controllable as serial devices within LINUX operating systems, although our virtual front panel software is not LINUX compatible.

Due to its added complexity, the D187 is supplied with dedicated control software.  Each of the 16 outputs of the D187 can be configured as a cathode, anode or inactive, so there are over 43 million potential electrode combinations.  Output configurations required for a particular experimental protocol may defined via our graphical user interface (GUI) and mapped within the D187 software as decimal, binary or hexadecimal values.  Previously defined configurations may then be activated via changes in the state of the 8 rear panel digital inputs.

Designed for a variety of research applications

The D188 and D189 are silent in operation and the software control panel allows the operator to toggle the LED indicator lights on and off. As a result, the subject of stimulation is not provided with any audible or visual cues of stimulus delivery.  In contrast, the D187 does produce a very low volume noise when the relays actuate and there is currently no means to turn off the LEDs, but this feature may be added in the future.  At the moment, we recommend the D187 is shielded or enclosed in a box when visual or audible cues need to be avoided.

Our electrode selectors are not supplied with any stimulator input or electrode connection cables, but it is possible to purchase additional plugs and cables to suit your specific requirements.  These allow direct connection to our complete range of isolated stimulators. We also offer output extension cables in order to increase the distance between the stimulating electrode and the D187/8/9 output sockets.

The Digitimer Remote Electrode Selectors are not medical devices and their use is restricted to research applications, however, the D188 and D187 have been designed to meet certain aspects of IEC 60601-1 relating to safety in human use.  The D189 is NOT recommended for human use.

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