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avr / am2302
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* add init function for am2302
* add some comments
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1 parent 52d5452 commit a74a69fdba32458d3a5608c8382095cc14933c0d
@Pascal Gollor Pascal Gollor authored on 29 Jan 2015
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 am2302.c
#define SENSOR_is_hi PIN_SENSOR & (1 << SENSOR)
#define SENSOR_is_low !(PIN_SENSOR & (1 << SENSOR))
 
 
/**
* @brief init avr for am2302 sda
*/
inline void am2302_init(void);
{
DDR_SENSOR &= ~(1 << SENSOR); // define as input
PORT_SENSOR &= ~(1 << SENSOR); // disable pullup
}
 
uint8_t am2302(uint16_t *humidity, uint16_t *temp)
{
if (SENSOR_is_low)
{
SENSOR_sda_in;
 
// Bus master has released time min: 20us, typ: 30us, max: 200us
uint8_t timeout = 200;
while(SENSOR_is_hi) {_delay_us(1); if (!timeout--) {return 2;}}
while(SENSOR_is_hi)
{
_delay_us(1);
if (!timeout--)
{
return 2;
}
}
 
// AM2302 response signal min: 75us typ:80us max:85us
timeout = 85;
while(SENSOR_is_low) {_delay_us(1); if (!timeout--) {return 3;}} // response to low time
while(SENSOR_is_low)
{
_delay_us(1);
if (!timeout--)
{
return 3;
}
} // response to low time
 
timeout = 85;
while(SENSOR_is_hi) {_delay_us(1); if (!timeout--) {return 4;}} // response to high time
while(SENSOR_is_hi)
{
_delay_us(1);
if (!timeout--)
{
return 4;
}
} // response to high time
 
 
/*
* time in us: min typ max
* signal 0,1 down time: 48 50 55
*/
 
uint8_t sensor_data[5]={0};
 
for(uint8_t i = 0; i < 5; i++)
{
uint8_t sensor_byte = 0;
for(uint8_t j = 1; j <= 8; j++) // get 8 bits from sensor
// get 8 bits from sensor
for(uint8_t j = 1; j <= 8; j++)
{
// wait for sensor response
timeout = 55;
while(SENSOR_is_low) {_delay_us(1); if (!timeout--) {return 5;}} // signal "0", "1" low time
while(SENSOR_is_low)
{
_delay_us(1);
 
// if timeout == 0 => sensor do not response
if (!timeout--)
{
return 5;
}
}
 
// wait 30 us to check if bit is logical "1" or "0"
_delay_us(30);
sensor_byte <<= 1; // add new lower byte
if (SENSOR_is_hi) // if sda high after 30us => bit=1 else bit=0
sensor_byte <<= 1; // add new lower bit
 
// If sda ist high after 30 us then bit is logical "1" else it was a logical "0"
// For a logical "1" sda have to be low after 75 us.
if (SENSOR_is_hi)
{
sensor_byte |= 1;
sensor_byte |= 1; // add logical "1"
timeout = 45; // 30us - 75us = 45us
while(SENSOR_is_hi) {_delay_us(1); if (!timeout--) {return 6;}}
 
while(SENSOR_is_hi)
{
_delay_us(1);
if (!timeout--)
{
return 6;
}
}
}
}
 
sensor_data[i] = sensor_byte;
}
 
// checksum
if ( ((sensor_data[0]+sensor_data[1]+sensor_data[2]+sensor_data[3]) & 0xff ) != sensor_data[4])
if ( ((sensor_data[0] + sensor_data[1] + sensor_data[2] + sensor_data[3]) & 0xff ) != sensor_data[4])
{
// debug output
//printf("%b %b %b %b %b %b" CR, sensor_data[0], sensor_data[1], sensor_data[2], sensor_data[3], sensor_data[4], ((sensor_data[0]+sensor_data[1]+sensor_data[2]+sensor_data[3]) & 0xff ));
return 7;
}
 
*humidity = (sensor_data[0]<<8) + sensor_data[1];
*temp = (sensor_data[2]<<8) + sensor_data[3];
*humidity = (sensor_data[0] << 8) + sensor_data[1];
*temp = (sensor_data[2] << 8) + sensor_data[3];
 
return 0;
}
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 am2302.h
#define SENSOR PC0
 
 
uint8_t am2302(uint16_t *humidity, uint16_t *temp);
 
inline void am2302_init(void);
 
 
#endif /* AM2302_H_ */
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main.c