Sutter Instrument Lambda 421, Operation Manual

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LAMBDA 421 OPERATION MANUAL – REV. 1.00N (20170623)
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still further reduce the current proportionally so their operation will be appear to be the
same as the other channels even though the range of currents available has been reduced.
3.7 Control via the DG-4 Interface
In order to understand the Lambda 421 it is important to know the way the DG-4 functions.
The DG-4 selects one of 4 filter paths for the light source. The filter values, in the DG-4
context, are actually just memory locations for the settings assigned to a filter value for
positioning the two galvanometers in the optical system. These settings could be any value in
the range of 0 to 4095. There are 16 available filter values in the DG-4 command set. Filter
values can be any number from 0 to 15. Filter 0 is normally reserved as a shutter function
and may have 0 stored for both galvanometers. Filters 1, 2, 3, and 4 typically have settings
that deliver the light through one of the four physical optical filters to the output port at full
power. Filters 5-12 are typically programmed to select one of the four filter paths at reduced
power. The standard setup uses filters 5-8 to select the filters used in 1-4 at 50% output
power and 9-12 are 1-4 at 33% output power. Filters 13-15 are available but normally defined
at the factory.
We have produced the same sort of control for four LEDs using the new USB DG-4 board.
This approach produces an LED version of the DG-4 that will run with existing software that
supports the DG-4. Since the DG-4 only works with one filter active at a time this command
set does not allow computer selection of more than 1 LED at a time. We have added some
basic logic circuits that convert the value of the filter selected to a signal that activates a
specific LED driver. Each LED is gated by a logic level signal and all LEDs will have the
analog input connected to the common DAC output on the DG-4 circuit board.
Since only one LED is activated by the DG-4 control at a time we can use a single DAC to
supply the current-controlling analog voltage for all four LEDs. In the DG-4 this DAC is
normally used for setting a galvanometer command signal. The DAC value is automatically
set to a value associated with a given filter when that filter is selected. We simply connected
that DAC output to the analog current control inputs of all 4 LED drivers and we now have a
system that automatically sets the desired current for each LED as it is selected. The value
for the DAC can be stored and read back using simple software commands.
The logic level signals that active the correct LED for each filter value are derived from the 4
bit binary output normally logic level output used by the DG-4 to indicate the selected filter.
We have added logic that converts the binary filter value into four separate TTL level
outputs, one for each LED. The original binary output is also available as before. The logic
was designed so that filter values 1-4 select the corresponding LEDs, 1-4. Filter values 5-8
and 9-12 also select LEDs 1-4. Filter values 13-15 select LEDs 1-3. Filter value 0 turns off all
LEDs. Looking at this in another way:
LED 1 is activated by filter values 1, 5, 9 and 13.
LED 2 is activated by filter values 2, 6, 10 and 14.
LED 3 is activated by filter values 3, 7, 11 and 15.
LED 4 is activated by filter values 4, 8, 12
Filter 0 does not active any LED.
The DG-4 controller stores two DAC values for each of the 16 possible filter values. We have
connected the analog output of one of these two DACs to the analog current control input for