python3 support for scd30.py, wiring example, root comment for installing clock stretching and more Readme.

README.md

@@ -4,9 +4,20 @@ Software to read out [Sensirion SCD30](https://www.sensirion.com/en/environmenta
 
 This software is licenced under GPLv3 by [UnravelTEC OG](https://unraveltec.com) (https://unraveltec.com), 2018.
 
-## Prerequsites 
+## Prerequsites
 
-### Python 
+### Enable I2C interface on Raspberry Pi
+`sudo raspi-config` navigate to `P5 I2C` and select `<Yes>`.
+
+### Wiring SCD30 to Raspberry Pi 3 B
+- SCD30: RX/SDA -> Pi: I2C1 SDA (GPIO2)
+- SCD30: TX/SCL -> Pi: I2C1 SCL (GPIO3)
+- SCD30: VIN -> Pi: 3.3V/5.5V (use one of PWR pinouts)
+- SCD30: GND -> Pi: GND (use one of GND pinouts)
+
+You might need to run the following commands as root e.g. by typing `sudo` before running a specific command.
+
+### Python
 
 Install the following python-libraries:
 
@@ -57,6 +68,8 @@ Remember: Maximum I2C speed for SCD30 is 100kHz.
 
 # Run program
 
+You might need to run the following as root e.g. by typing `sudo` before running the script.
+
 ```
 python scd30.py
 ```

py3scd30.py

@@ -0,0 +1,183 @@
+#!/usr/bin/env python
+# coding=utf-8
+#
+# Copyright © 2018 UnravelTEC
+# Michael Maier <[email protected]>
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+#
+# If you want to relicense this code under another license, please contact [email protected].
+
+# hints from https://www.raspberrypi.org/forums/viewtopic.php?p=600515#p600515
+
+from __future__ import print_function
+
+# This module uses the services of the C pigpio library. pigpio must be running on the Pi(s) whose GPIO are to be manipulated.
+# cmd ref: http://abyz.me.uk/rpi/pigpio/python.html#i2c_write_byte_data
+import pigpio # aptitude install python-pigpio
+import time
+import struct
+import sys
+import crcmod # aptitude install python-crcmod
+
+
+def eprint(*args, **kwargs):
+  print(*args, file=sys.stderr, **kwargs)
+
+PIGPIO_HOST = '::1'
+PIGPIO_HOST = '127.0.0.1'
+
+pi = pigpio.pi(PIGPIO_HOST)
+if not pi.connected:
+  eprint("no connection to pigpio daemon at " + PIGPIO_HOST + ".")
+  exit(1)
+
+I2C_SLAVE = 0x61
+I2C_BUS = 1
+
+try:
+  pi.i2c_close(0)
+except:
+  if sys.exc_info()[1] and str(sys.exc_info()[1]) != "'unknown handle'":
+    eprint("Unknown error: ", sys.exc_type, ":", sys.exc_info()[1])
+
+try:
+	h = pi.i2c_open(I2C_BUS, I2C_SLAVE)
+except:
+	eprint("i2c open failed")
+	exit(1)
+
+# read meas interval (not documented, but works)
+
+def read_n_bytes(n):
+
+  try:
+    (count, data) = pi.i2c_read_device(h, n)
+  except:
+    eprint("error: i2c_read failed")
+    exit(1)
+
+  if count == n:
+    return data
+  else:
+    eprint("error: read measurement interval didnt return " + str(n) + "B")
+    return False
+
+def i2cWrite(data):
+  try:
+    pi.i2c_write_device(h, data)
+  except:
+    eprint("error: i2c_write failed")
+    return -1
+  return True
+
+
+def read_meas_interval():
+  ret = i2cWrite([0x46, 0x00])
+  if ret == -1:
+    return -1
+
+  try:
+    (count, data) = pi.i2c_read_device(h, 3)
+  except:
+    eprint("error: i2c_read failed")
+    exit(1)
+
+  if count == 3:
+    if len(data) == 3:
+      interval = int(data[0])*256 + int(data[1])
+      #print "measurement interval: " + str(interval) + "s, checksum " + str(data[2])
+      return interval
+    else:
+      eprint("error: no array len 3 returned, instead " + str(len(data)) + "type: " + str(type(data)))
+  else:
+    "error: read measurement interval didnt return 3B"
+
+  return -1
+
+read_meas_result = read_meas_interval()
+if read_meas_result == -1:
+  exit(1)
+
+if read_meas_result != 2:
+# if not every 2s, set it
+  eprint("setting interval to 2")
+  ret = i2cWrite([0x46, 0x00, 0x00, 0x02, 0xE3])
+  if ret == -1:
+    exit(1)
+  read_meas_interval()
+
+
+#trigger cont meas
+# TODO read out current pressure value
+pressure_mbar = 972
+LSB = 0xFF & pressure_mbar
+MSB = 0xFF & (pressure_mbar >> 8)
+#print ("MSB: " + hex(MSB) + " LSB: " + hex(LSB))
+#pressure_re = LSB + (MSB * 256)
+#print("press " + str(pressure_re))
+pressure = [MSB, LSB]
+
+pressure_array = ''.join(chr(x) for x in [pressure[0], pressure[1]])
+
+#pressure_array = ''.join(chr(x) for x in [0xBE, 0xEF]) # use for testing crc, should be 0x92
+#print(pressure_array)
+
+f_crc8 = crcmod.mkCrcFun(0x131, 0xFF, False, 0x00)
+
+#print("CRC: " + hex(f_crc8))
+i2cWrite([0x00, 0x10, pressure[0], pressure[1], f_crc8(b'123456789')])
+
+# read ready status
+while True:
+  ret = i2cWrite([0x02, 0x02])
+  if ret == -1:
+    exit(1)
+
+  data = read_n_bytes(3)
+  if data == False:
+    time.sleep(0.1)
+    continue
+
+  if data[1] == 1:
+    #print "data ready"
+    break
+  else:
+    #eprint(".")
+    time.sleep(0.1)
+
+#read measurement
+i2cWrite([0x03, 0x00])
+data = read_n_bytes(18)
+
+#print "CO2: "  + str(data[0]) +" "+ str(data[1]) +" "+ str(data[3]) +" "+ str(data[4])
+
+struct_co2 = struct.pack('>BBBB', data[0], data[1], data[3], data[4])
+float_co2 = struct.unpack('>f', struct_co2)[0]
+
+struct_T = struct.pack('>BBBB', data[6], data[7], data[9], data[10])
+float_T = struct.unpack('>f', struct_T)
+
+struct_rH = struct.pack('>BBBB', data[12], data[13], data[15], data[16])
+float_rH = struct.unpack('>f', struct_rH)[0]
+
+if float_co2 > 0.0:
+  print("gas_ppm{sensor=\"SCD30\",gas=\"CO2\"} %f" % float_co2)
+
+print("temperature_degC{sensor=\"SCD30\"} %f" % float_T)
+
+if float_rH > 0.0:
+  print("humidity_rel_percent{sensor=\"SCD30\"} %f" % float_rH)
+
+pi.i2c_close(h)