Since finding a cheap alternative to PLC whilst using an industrial protocol is a popular idea the Raspberry Pi has caught many eyes on doing this. I posted once on reading a temperature sensor and serving it up on the Pi using ModbusTCP. This time I expound on it and show you how to control something. In this case it will be a PC 12v fan.
Parts:
- 1 x Raspberry pi
- 1 x Darlington Transistor
- 1 x PC Fan (with about 500ma load)
- 1 x 12v DC Power Supply
Setup:
- Installing pymodbus and dependencies:
- sudo apt-get install python-pymodbus python-twisted-conch
- Wire up your Fan, LED, or motor
- View my code from Github.
Video of what I did:
Source Code:
from pymodbus.server.async import StartTcpServer
from pymodbus.device import ModbusDeviceIdentification
from pymodbus.datastore import ModbusSequentialDataBlock, ModbusSlaveContext, ModbusServerContext
from pymodbus.transaction import ModbusRtuFramer, ModbusAsciiFramer
from twisted.internet.task import LoopingCall
from threading import Thread
import pid
import threading
from time import sleep
import RPi.GPIO as GPIO
import os
os.system('modprobe w1-gpio')
os.system('modprobe w1-therm')
#set up Raspberry GPIO
GPIO.setmode(GPIO.BCM)
GPIO.setwarnings(False)
GPIO.setup(25,GPIO.OUT)
pwm = GPIO.PWM(25,60)
pwmDutyCycle=100
pwm.start(pwmDutyCycle)
temperaturePoll = None
class Temp(Thread):
"""
A class for getting the current temp of a DS18B20
"""
def __init__(self, fileName=''):
Thread.__init__(self)
super(Temp, self).__init__()
self._stop = threading.Event()
self.tempDir = '/sys/bus/w1/devices/'
list = os.listdir(self.tempDir)
if(list[0][:2]=="28"):
fileName=list[0]
self.fileName = fileName
self.currentTemp = -999
self.correctionFactor = 1;
self.enabled = True
self.Run=True
def run(self):
while self.isEnabled():
try:
f = open(self.tempDir + self.fileName + "/w1_slave", 'r')
except IOError as e:
print "Error: File " + self.tempDir + self.fileName + "/w1_slave" + " does not exits"
return;
lines=f.readlines()
crcLine=lines[0]
tempLine=lines[1]
result_list = tempLine.split("=")
temp = float(result_list[-1])/1000 # temp in Celcius
temp = temp + self.correctionFactor # correction factor
#if you want to convert to Celcius, comment this line
temp = (9.0/5.0)*temp + 32
if crcLine.find("NO") > -1:
temp = -999
self.currentTemp = temp
#print "Current: " + str(self.currentTemp) + " " + str(self.fileName)
sleep(.5)
#returns the current temp for the probe
def getCurrentTemp(self):
return self.currentTemp
#setter to enable this probe
def setEnabled(self, enabled):
self.enabled = enabled
#getter
def isEnabled(self):
return self.enabled
def updating_writer(a):
context = a[0]
register = 3
slave_id = 0x00
address = 0x00
global pwmDutyCycle,temp
#uncomment to debug temperature
print temp.getCurrentTemp()
values = [int(pwmDutyCycle),temp.getCurrentTemp()*100]
context[slave_id].setValues(register,address,values)
def read_context(a):
context = a[0]
register = 3
slave_id = 0x00
address = 0x00
value = context[slave_id].getValues(register,address)[0]
global pwmDutyCycle
if(value!=pwmDutyCycle):
print value
pwmDutyCycle=value
pwm.ChangeDutyCycle(pwmDutyCycle)
def main():
store = ModbusSlaveContext(
di = ModbusSequentialDataBlock(0, [0]*100),
co = ModbusSequentialDataBlock(0, [0]*100),
hr = ModbusSequentialDataBlock(0, [0]*100),
ir = ModbusSequentialDataBlock(0, [0]*100))
context = ModbusServerContext(slaves=store, single=True)
identity = ModbusDeviceIdentification()
identity.VendorName = 'pymodbus'
identity.ProductCode = 'PM'
identity.VendorUrl = 'http://github.com/simplyautomationized'
identity.ProductName = 'pymodbus Server'
identity.ModelName = 'pymodbus Server'
identity.MajorMinorRevision = '1.0'
time = 5 # 5 seconds delaytime = 5 # 5 seconds delay
writer = LoopingCall(read_context,a=(context,))
loop = LoopingCall(updating_writer, a=(context,))
loop.start(.5) # initially delay by time
writer.start(.1)
StartTcpServer(context, identity=identity)#, address=("localhost", 502))
#cleanup async tasks
temp.setEnabled(False)
loop.stop()
writer.stop()
GPIO.cleanup()
if __name__ == "__main__":
temp = Temp()
temp.start()
main()
