Sim800 hardware design v1.05

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4.14. ADC
Table 27: Pin definition of the ADC
Pin name Pin number Description
ADC 25 Analog to Digital Converter
SIM800_Hardware Design_V1.05 48 2014-03-25
SIM800 provides an auxiliary ADC, which can be used to measure the voltage. User can use AT command
“AT+CADC” to read the voltage value. For details of this AT command, please refer to document [1].
Table 28: 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 29: Pin definition of the PWM
Pin name
Pin number Description
PWM1/GPIO22 35 PWM1, multiplex with GPIO22
PWM2/GPIO23 36 PWM2, multiplex with GPIO23
Note: SIM800 can only support 1 PWM synchronously, if customer set PIN 35 as PWM, so PIN36 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: