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“AT+CADC” to read the voltage value. For details of this AT command, please refer to
document [1].
Table 29: ADC specification
Parameter
Min
Typ
Max
Unit
Voltage range
0
-
2.8
V
ADC Resolution
-
10
-
bits
Sampling rate
-
-
1.0833
MHz
ADC precision
10
20
mV
Note: the voltage should less than 2.8V, or the ADC may be damaged.
4.15
PWM
Table 30: Pin definition of the PWM
Pin name
Pin number
Description
PWM1
42
PWM1, multiplex with GPIO4
PWM2
41
PWM2, multiplex with GPIO3
Note: SIM808 can only support 1 PWM synchronously, if customer set PIN 42 as PWM, so PIN41 can only be used as GPIO.
PWM output frequency varies from 0 to 2KHz.Two 7-bit unsigned binary parameters are used for the output
period and for the duty cycle. The AT command “AT + SPWM” is used to set the output period and duty cycle of
the PWM. For details, please refer to
document [1].
A typical circuit of the PWM drives buzzer is shown in the following figure:
4.7K
47K
VBAT
PWM
Figure 47: Reference circuit of PWM drive buzzer
Table 31: Buzzer output characteristics
Parameter
Min
Typ
Max
Unit
Working voltage
2.5
2.8
2.9
V
Working current
16
mA
Note: PWM pin must keep low when module in the boot process.
Table 32: PWM multiplex function
SIM808_Hardware Design_V1.00 2014.03.27
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