5 • Circuit Descriptions
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80116-443
10.16
LED display
For the display, a 7-segment display for 3 characters was chosen. In addi-
tion, there are four other LEDs for lighting up the buttons and four for dis-
playing the various statuses.
Control of the LED cathodes is via the data bus of Port B and a driver,
ULN2803. The LED anodes are controlled by Port T via the transistors of
type BC817. Control is sequential with a basic frequency of 62 Hz.
The LED "ON" time can be changed via the brightness setting in the service
mode. The LED "ON" time can be adjusted to between 0.1 ms and 1 ms.
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