Note: Code is cross-compiled in windows 10.
Code:
package main
import (
"fmt"
"io"
"log"
"net/http"
aosong "github.com/d2r2/go-aosong"
i2c "github.com/d2r2/go-i2c"
)
const i2CAddress = 0x5c
const i2CBus = 1
// Server struct
type Server struct {
Sensor *aosong.Sensor
I2C *i2c.I2C
}
func main() {
var err error
s := Server{Sensor: aosong.NewSensor(aosong.AM2320)}
s.I2C, err = i2c.NewI2C(i2CAddress, i2CBus)
if err != nil {
log.Printf(err.Error())
}
fmt.Println(s.Sensor.ReadRelativeHumidityAndTemperature(s.I2C))
defer s.I2C.Close()
}
Debug info:
2019-02-12T10:29:19.692 [ i2c] DEBUG Write 3 hex bytes: [030004]
2019-02-12T10:29:19.697 [ i2c] DEBUG Read 8 hex bytes: [0304012500d92045]
2019-02-12T10:29:19.698 [ i2c] DEBUG Read 8 hex bytes: [0000000000000000]
CRCs doesn't match: CRC from sensor(0) != calculated CRC(6912)
Any ideea why the CRC from sensor is 0?
I am able to read the sensor on the same bus with the same address with a python script.
#!/usr/bin/python
import posix
from fcntl import ioctl
import time
class AM2320:
I2C_ADDR = 0x5c
I2C_SLAVE = 0x0703
def __init__(self, i2cbus = 1):
self._i2cbus = i2cbus
@staticmethod
def _calc_crc16(data):
crc = 0xFFFF
for x in data:
crc = crc ^ x
for bit in range(0, 8):
if (crc & 0x0001) == 0x0001:
crc >>= 1
crc ^= 0xA001
else:
crc >>= 1
return crc
@staticmethod
def _combine_bytes(msb, lsb):
return msb << 8 | lsb
def readSensor(self):
fd = posix.open("/dev/i2c-%d" % self._i2cbus, posix.O_RDWR)
ioctl(fd, self.I2C_SLAVE, self.I2C_ADDR)
# wake AM2320 up, goes to sleep to not warm up and affect the humidity sensor
# This write will fail as AM2320 won't ACK this write
try:
posix.write(fd, b'\0x00')
except:
pass
time.sleep(0.001) #Wait at least 0.8ms, at most 3ms
# write at addr 0x03, start reg = 0x00, num regs = 0x04 */
posix.write(fd, b'\x03\x00\x04')
time.sleep(0.0016) #Wait at least 1.5ms for result
# Read out 8 bytes of result data
# Byte 0: Should be Modbus function code 0x03
# Byte 1: Should be number of registers to read (0x04)
# Byte 2: Humidity msb
# Byte 3: Humidity lsb
# Byte 4: Temperature msb
# Byte 5: Temperature lsb
# Byte 6: CRC lsb byte
# Byte 7: CRC msb byte
data = bytearray(posix.read(fd, 8))
# Check data[0] and data[1]
if data[0] != 0x03 or data[1] != 0x04:
raise Exception("First two read bytes are a mismatch")
# CRC check
if self._calc_crc16(data[0:6]) != self._combine_bytes(data[7], data[6]):
raise Exception("CRC failed")
# Temperature resolution is 16Bit,
# temperature highest bit (Bit15) is equal to 1 indicates a
# negative temperature, the temperature highest bit (Bit15)
# is equal to 0 indicates a positive temperature;
# temperature in addition to the most significant bit (Bit14 ~ Bit0)
# indicates the temperature sensor string value.
# Temperature sensor value is a string of 10 times the
# actual temperature value.
temp = self._combine_bytes(data[4], data[5])
if temp & 0x8000:
temp = -(temp & 0x7FFF)
temp /= 10.0
humi = self._combine_bytes(data[2], data[3]) / 10.0
return (temp, humi)
am2320 = AM2320(1)
(t,h) = am2320.readSensor()
print t, h
