參數(shù)資料
型號(hào)： 30770
廠商： Dresden Elektronik
文件頁(yè)數(shù)： 45/74頁(yè)
文件大?。?/td> 2001K
描述： SET DERFNODE FOR AVR HOUSING
標(biāo)準(zhǔn)包裝： 1
User Manual
Version 1.1
2011-07-15
 
  deRFnode and deRFgateway
 
 
 
 
dresden elektronik
ingenieurtechnik gmbh
Enno-Heidebroek-Str. 12
12 7 Dr
n
rm  n
Tel.: +49 351  31 85 00
Fax: +49 351  3 18 50 10
wireless@dresden-elektronik.de
www. r
n- l k r nik.
Page 45 of 56
 
9.4.4. Measuring the battery voltage
The VBAT signal may be used to monitor the current battery voltage using the MCUs internal
A/D-converter. This requires a reference voltage. On ARM MCUs it must be provided exter-
nally on Pin3 which is available on the X8-Header at Pin 32. It is suggested to shortcut it to
VCC which is available on the same Header on Pins 2 and 33. Basically AVR MCUs can
handle external reference voltages too but we recommend using the internal reference volt-
age since it avoids additional external shortcut connections and enables a more precise
measurement. However in both cases during measurement, the GPIO-Pin 34 (e.g. on X8-
Header Pin 15) must not be used otherwise.
The measurement process includes:
(1) Initialization of the ADC,
(2) activation of the required ADC channel (0),
(3) perform the measurement,
(4) shut down the ADC.
 
For ARM MCUs, in peripherals/adc/adc.c the required library functions are to be
found and their invocation sequence may look like: 
#define BOARD_ADC_FREQ 300000        // ADC Frequency  
#define ADC_STARTUP_TIME_MAX    20   // returning from Idle mode (?/SPAN>s) 
#define ADC_TRACK_HOLD_TIME_MIN 600  // Track&hold Acquisition Time (ns) 
unsigned int adc_out, V_bat; 
const Pin pin = {1<<27, AT91C_BASE_PIOB, AT91C_ID_PIOB, PIO_INPUT,  
  PIO_DEFAULT};
PIO_Configure(pin, 1); 
ADC_Initialize( AT91C_BASE_ADC, 
  AT91C_ID_ADC,
  AT91C_ADC_TRGEN_DIS,
  0,
  AT91C_ADC_SLEEP_NORMAL_MODE,
  AT91C_ADC_LOWRES_10_BIT,
  BOARD_MCK,
  BOARD_ADC_FREQ,
  ADC_STARTUP_TIME_MAX,
  2*ADC_TRACK_HOLD_TIME_MIN);
 
ADC_EnableChannel(AT91C_BASE_ADC, ADC_CHANNEL_0); 
ADC_StartConversion(AT91C_BASE_ADC); 
// wait for conversion termination 
while (!ADC_IsChannelInterruptStatusSet( ADC_GetStatus(AT91C_BASE_ADC),              
  ADC_CHANNEL_0)) ;
  // perform measurement      
adc_out = ADC_GetConvertedData(AT91C_BASE_ADC, ADC_CHANNEL_0);
 
// convert the measured value to real voltage (mV) 
// voltage divider <-> V_bat = 4.73*V_meas 
// max. resolution 10bit, V_ref=3.3V <-> V_ref/0x3FF = V_meas/adc_out 
// <-> V_bat = 15.24*adc_out ~ (61*V_meas)/4  
V_bat = (61*meas)/4;
  // deactivate the ADC for power saving
ADC_DisableChannel(AT91C_BASE_ADC, ADC_CHANNEL_0); 
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