71M6521 Demo Board User’s Manual
Revision 2.18
© 2005-2009 TERIDIAN Semiconductor Corporation
Page: 63 of 111
Figure 2-12: LCD Connections
2.3.6 OPTICAL INTERFACE
The 71M6521 IC is equipped with two pins supporting the optical interface: OPT_TX and OPT_RX. The
OPT_TX pin can be used to drive a visual or IR light LED with up to 20mA, a series resistor (R
2
2-13) helps limiting the current). The OPT_RX pin can be connected to the collector of a photo-transistor, as
shown in Figure 2-13.
Figure 2-13: Optical Interface Block Diagram
J12 on the Demo Boards has all the provisions for connecting the IR LED and photo-transistor (see Figure
2-14). Depending on the required LED current, R79 may have to be scaled. Similarly, R84 may be scaled or
removed, depending on the current generated by the photo-transistor.
segments
6521
LCD
commons
OPT_TX
R
2
R
1
OPT_RX
71M6521
V3P3D
Phototransistor
LED
100k
Ω
100pF
V3P3D
OPT_TX
R
2
R
1
OPT_RX
71M6521
V3P3D
Phototransistor
LED
100k
Ω
100pF
V3P3D