Crossbow Technology MIB300, Руководство пользователя

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MPR/MIB User’s Manual
Wireless Sensor Networks
Doc. # 7430-0021-06 Rev. A Page 24
To compute the battery voltage:
1. Set the BAT_MON processor pin (PA5/AD5) to HI.
2. Program the application code to measure ADC Channel 7.
3. Compute battery voltage, V
batt
, from Channel 7’s data by:
Count ADC FS ADC V V
ref batt
_ _
× =
where:
V
batt
= Battery voltage
ADC_FS = 1024
V
ref
= External voltage reference = 1.223 V
ADC_Count = Data from the ADC measurement of Channel 7
6.5 MICA2DOT Battery Voltage Monitor
Unlike the MICAz and the MICA2, the MICA2DOT uses a Schottky reference diode (S103AW)
as a voltage reference that can be used to measure battery voltage (
V
batt
). Since the eight-channel,
ATMega128L ADC uses the battery voltage as a full-scale reference, the ADC full scale
(
ADC_FS ) voltage value changes as the battery voltage changes. In order to calibrate the battery
voltage an external voltage reference ( V
ref
) is required.
To compute the battery voltage:
1. Set processor pins PW7 (PC7/A15) to LO and PW6 (PC6/A14) to HI.
2. Program the application code to measure ADC Channel 1 (ADC1).
3. Compute battery voltage, V
batt
, from channel 1’s data by:
Count ADC FS ADC V V
ref batt
_ _
× =
where:
V
batt
= Battery voltage
ADC_FS = 1024
V
ref
= External voltage reference = 0.6 volts
ADC_Count = Data from the ADC measurement of Channel 1