UM0943
Hardware description
Doc ID 17476 Rev 1
5/22
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7-segment (+dot) display (11)
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STLED325 (12)
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32.768 kHz RTC crystal (13)
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8 discrete LEDs for brightness (14)
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UART pinouts (15)
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Wake-up key: WAKE UP (16)
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DC buzzer for alarm function (17)
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Super cap for backup (18) (battery backup can be replaced by a lithium ion battery for
longer backup time)
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System reset switch (19)
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DC power jack (20)
1.1
Power supply unit
The board is equipped with a DC jack into which an external adaptor (9 V-18 V, 500 mA) can
be plugged. The board consists of a 5 V output switching regulator for higher efficiency and
a 3.3 V output linear regulator onboard to give regulated outputs, as required. The board
may also be powered up using a PC laptop adaptor. The user must ensure that the external
PSU jack is of the center positive type, although reverse polarity does not damage the
demonstration board. A bicolor “PWR/STBY” LED (D4) is shown in
. When in
normal operation the PWR/STBY LED is green and turns red when the system is in standby
condition.
Figure 4.
DC power jack
www.BDTIC.com/ST
