Neurotechnology Research Systems
Optogenetic Controller
- 22 -
7.4
Current or Voltage Limit
In current mode, the optogenetic controller can output more current than some LEDs can handle.
To reduce the risk of damaging your LED, the current limit can be set. There are default values for
Plexon’s LED modules that can be selected, or a custom value can be entered. Reducing the current
limit also has the additional benefit of increasing your resolution because the output is an 8 bit
value ranging from 0 to the current limit. So if your limit is 1000mA, your resolution will be
approximately 3.9mA. Reducing the limit to 300mA makes your resolution 1.2mA.
In voltage mode, the output can range from 0-5V. If you know that you will never need a voltage
above a smaller value, you can set the voltage limit to increase the resolution.
7.5
Pattern Source
There are two options within the Pattern drop down: Manual Mode and File.
7.5.1
Manual Mode
In manual mode, a value is entered for the amplitude of a constant output. The units are mV or mA
depending on if the controller is in voltage or current mode respectively.
7.5.2
File
Arbitrary waveform patterns are stimulation patterns that are defined in text files with a .opt
extension. From the Pattern drop down list, select File. Then click on the folder in the File box to
browse to the previously created file. When the file is opened, a graphical representation of the
arbitrary waveform is displayed and the file is automatically loaded into the controller.
7.5.2.1
Creating a stimulation pattern file
The controller operates at 10kHz, meaning the stimulation output is updated every 100µs. A user-
defined pattern file is simply a list of stimulation output values that are desired every 100µs. Each
value is followed by a “line feed” and a “carriage return.” This means that if you want to maintain
the same value for a longer period of time, you must repeat the value (desired time/100µs) times.
For example, stimulating 100mA for 1ms would require 10 consecutive lines of “100.”
7.6
Repetitions and Count
A file based pattern can be played continuously or a finite number of time based on the setting of
the Repetitions parameter. When finite Repetitions are selected, the number of repetitions may be
set using the Count parameter. Note that these controls are not visible when Manual Mode is
selected as the pattern source.