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Assuming:
-
a voltage of 5V across the series combination of the LED and resistor and
-
a 1.6V drop across the LED
Find the design value of the current limiting resistor such that the current
through the LED will be approximately 7 mA. Select a resistor
from the parts bin that is as close as possible to your
design value. Assemble the portion of the transmitter prior to the
potentiometer (R2) noting that the longer terminal of the LED is the
anode (See Figure 
).
Figure: Diode Types with Polarity Indication
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