T W R - S 0 8 L L / L H U S E R G U I D E
A P R I L 2 7 , 2 0 1 0
U S E R G U I D E
13
VDD1 Enable
The VDD1 option jumper disconnects the BUZZER, and Light sensor from board power for
low-power operation. Figure 9: below shows the option header settings for use with the
VDD1_EN
Buzzer
The TWR-S08 board provides an externally modulated piezo-buzzer for audible applications.
A push-pull drive circuit allows the target MCU to easily drive the buzzer at a center frequency
of 2400 Hz. Figure 9: below shows the option header settings for use with the buzzer.
Light Sensor
A surface-mount phototransistor, at RZ1, provides light sensitive, variable input for user
applications. Current flow within the phototransistor is inversely proportional to light intensity
incident on the surface of the device. A rail-to-rail OP amp at U5 boosts the photocell output to
useable levels. Figure 9: below shows the option header settings for use with the light sensor
Figure 9: USER1 Option Header, JP7
Signal
ON
OFF
Buzzer
PTC2/TPM1CH0
Enabled (*)
Disabled
RZ1
PTA6/ADP6
Enabled (*)
Disabled
VDD1
VDD
Enabled (*)
Disabled
JP7
(*)
– Default Position
CAUTION:
SW1 and RZ1 share a common MCU signal input. If both components are
enabled at the same time, SW 1 may not function properly.
Pushbutton Switches
The TWR-S08 applies 4, normally open, push-button switches for user input. Each push-
button switch is configured for active-low operation. A 22pF capacitor is applied to each push-
button switch to minimize switch bounce. An external pull-up is applied to SW4 for use as and
IRQ* input; however, no bias is applied to the remaining push-button inputs. Use of target
MCU internal pull-ups is required for proper operation.
Figure 10 below shows the user switch connections to the target MCU. Since each push-
button switch is normally-open, no option header is applied.