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APPENDIX A
Appendix A: Adding a LED to Amplifier Boards
All RHD2000 amplifier boards provide solder holes for +3.3 V power (“VDD”) and ground
(“GND”). A series combination of an LED and a current-limiting resistor should be sol-
dered in series between these two holes, as shown in the photo to the right.
One side of the LED will have a flat edge. The terminal on this side should be connected
to ground. The other terminal should be connected through the resistor to power.
The value of the series resistor is chosen using the following equation:
R = (V
DD
– V
LED
) / I
LED
The power supply voltage V
DD
will be approximately 3.3 V. Most red, green, or yellow LEDs have voltage drops (V
LED
) around 2.0 V when they are active.
Blue and white LEDs have voltage drops greater than 3.3 V, so they cannot be used effectively with these boards.
The current I
LED
required to produce a reasonable amount of light depends on the type of LED. Older LEDs require 10-20 mA of current, while newer
“low power” LEDs produce the same amount of light with 1-2 mA of current.
This range of parameters yields resistances in the range of 65 Ω to 1300 Ω. It is recommended that different values be tried experimentally to deter-
mine a value of current that produces desired light levels before final soldering.
Some amplifier boards provide an additional solder hole for the RHD2000 auxiliary digital output pin
auxout
, labeled “DO” on the circuit board. (The
RHD2164 amplifier board and the 16-channel RHD2132 amplifier board with 18-pin electrode connector omit this connection to save space.)
It is possible to control the
auxout
pin in real time using a selected digital input signal on the SmartBox
™
. Under the “Configure” tab in the SmartBox
™
interface software there is a button labeled “Configure Realtime Control” in the “Auxiliary Digital Output Pins” box. Clicking this button opens a dialog
that allows users to enable real-time control and to select which digital input will be used to control the digital output pin on particular chips.
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