DrJoe Geschrieben December 19, 2018 at 08:47 Share Geschrieben December 19, 2018 at 08:47 Hallo, bitte um mithilfe wenn der ds18b20 sensor mit dem Python script Temperaturen unter null °C ausliest, ergeben sich fehlerhafte werte: Sensor2: 4094.81 °C ? Herausgefunden habe ich das durch einfaches tauschen der Position der sensoren von innen/aussen. hat jemand eine Idee? hier der Code: #!/usr/bin/env python # -*- coding: utf-8 -*- HOST = "localhost" PORT = 4223 UID = "GGW" # Change XYZ to the UID of your One Wire Bricklet import time from tinkerforge.ip_connection import IPConnection from tinkerforge.bricklet_one_wire import BrickletOneWire if __name__ == "__main__": ipcon = IPConnection() # Create IP connection ow = BrickletOneWire(UID, ipcon) # Create device object ipcon.connect(HOST, PORT) # Connect to brickd # Don't use device before ipcon is connected ids = ow.search_bus().identifier print ids #id 13114784581154432808L ow.write_command(13114784581154432808L, 78) # WRITE SCRATCHPAD ow.write(0) # ALARM H (unused) ow.write(0) # ALARM L (unused) ow.write(127) # CONFIGURATION: 12 bit mode # Read temperature 2 times for i in range(2): ow.write_command(13114784581154432808L, 68) # CONVERT T (start temperature conversion) time.sleep(2) # Wait for conversion to finish ow.write_command(13114784581154432808L, 190) # READ SCRATCHPAD t_low = ow.read().data t_high = ow.read().data temperature1 = ('{:6.2f}'.format((t_low | (t_high << ) / 16.0)) print "Sensor1: %s °C" % temperature1 ipcon.disconnect() if __name__ == "__main__": ipcon = IPConnection() # Create IP connection ow = BrickletOneWire(UID, ipcon) # Create device object ipcon.connect(HOST, PORT) # Connect to brickd # Don't use device before ipcon is connected ow.write_command(15348569994255425064L, 78) ow.write(0) # ALARM H (unused) ow.write(0) # ALARM L (unused) ow.write(127) # CONFIGURATION: 12 bit mode # Read temperature 2 times for i in range(2): ow.write_command(15348569994255425064L, 68) time.sleep(2) # Wait for conversion to finish ow.write_command(15348569994255425064L, 190) t_low = ow.read().data t_high = ow.read().data temperature2 = ('{:6.2f}'.format((t_low | (t_high << ) / 16.0)) print "Sensor2: %s °C" % temperature2 ipcon.disconnect() Ausgabe: (15348569994255425064L, 13114784581154432808L) Sensor1: 20.25 °C Sensor1: 20.31 °C Sensor2: 4095.69 °C Sensor2: 4095.69 °C ? Zitieren Link zu diesem Kommentar Share on other sites More sharing options...
rtrbt Geschrieben December 19, 2018 at 11:05 Share Geschrieben December 19, 2018 at 11:05 Das ist ein Bug in unserem Beispiel. Damit negative Temperaturen funktionieren, muss der Code wie folgt abgeändert werden: temperature1 = ('{:6.2f}'.format((t_low | (t_high << ) / 16.0)) muss stattdessen temperature1 = (t_low | (t_high << ) if temperature1 > 1 << 12: temperature1 -= 1 << 16 # Negative 12-bit values are sign-extended to 16-bit two's complement. temperature1 /= 16.0 # 12 bit mode measures in units of 1/16°C. temperature1 = '{:6.2f}'.format(temperature1) sein, bei temperature2 analog. Das Problem ist, dass der Temperatursensor eine 12 Bit lange Zahl in Zweier-Komplement-Form ausgibt (und die aufgeblasen auf 16 Bit, damit sie zwei Byte füllt). Das hat der Beispielcode bisher nicht beachtet. Ich behebe das mal in den Beispielen aller Sprachen. Zitieren Link zu diesem Kommentar Share on other sites More sharing options...
DrJoe Geschrieben December 19, 2018 at 17:56 Autor Share Geschrieben December 19, 2018 at 17:56 it works: (15348569994255425064L, 13114784581154432808L) Sensor1: 20.69 °C Sensor1: 20.69 °C Sensor2: -0.25 °C Sensor2: -0.25 °C Vielen Dank Zitieren Link zu diesem Kommentar Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.