Category:PCB Assembly Raspberry Pi

Group Administrators: 1 | Group Member: 47 | Group Threads: 44

The Raspberry Pi is a series of small single-board computers developed in the United Kingdom by the Raspberry Pi Foundation to promote the teaching of basic computer science in schools and in developing countries.

Thread Reply
Control a fan based on the current temperature with a Raspberry Pi Reply 2017-01-21 20:06:15
1K+ views
1 comments
516 likes

frmendozat

Leave A Message

Follow


Requirements


  • Raspberry Pi
    • Used in article: Model B Revision 1.0 with Raspbian (Debian GNU/Linux 7.6 (wheezy))
  • I2C temperature sensor
    • Used in article: TMP102
  • Method to connect Raspberry Pi to internet
    • Use in article: Raspberry Pi wired directly to router
  • Google account to create and access sheets
  • NMOS or NPN transistor capable of handling the voltage and current requirements of the fan
  • Schottky diode
  • Small DC fan
    • Used in article: 12V/600mA fan
Set Up the HardwareTemp sensor


Follow the instructions in this article to connect a temperature sensor to the Raspberry Pi.
Fan
Follow the wiring diagram below to connect the Raspberry Pi to the temp sensor and to the fan through the transistor. The diode is there to prevent the fan from damaging the transistor due to potential voltage flyback when turning the fan off. A diode in this configuration is sometimes called asnubber. You have to cut the ground wire feeding the fan in order to put the transistor in series. The transistor is acting as alow-side switchin this configuration.
The maximum current of the Pi GPIO output is 16mA. This means the transistor must have a high enough hFE to conduct the current needed to run the fan. Size the base resistor to limit the amount of current the Pi delivers to the transistor to avoid damage. I used 180 ohms which would give a base current of approximately (3.3-0.7)/180 = 14.4mA. The transistor I selected has an hFE of 150 when conducting 2A, so switching a 600mA load is no problem.

Software

I2C

Follow the article here to setup I2C to communicate to the temp sensor.

Installing GPIO capability

Type the following in the Pi terminal to install GPIO capability: sudo apt-get install python-rpi.gpio

Testing Connections

Upload the following Python program to the Raspberry Pi in order to test the fan control from the GPIO. Run the script "turn_fan_on.py" or "turn_fan_off.py" in order to verify the connections.

turn_fan_on.py

 

                    import RPi.GPIO as GPIO

GPIO.setwarnings(False)
GPIO.setmode(GPIO.BCM)
FAN_PIN = 23
GPIO.setup(FAN_PIN, GPIO.OUT)
GPIO.output(FAN_PIN, True) 

turn_fan_off.py

 

                    import RPi.GPIO as GPIO

GPIO.setwarnings(False)
GPIO.setmode(GPIO.BCM)
FAN_PIN = 23
GPIO.setup(FAN_PIN, GPIO.OUT)
GPIO.output(FAN_PIN, False) 

Controlling the fan based on temperature

The following script implements some logic that turns on the fan when the temperature has risen above TEMP_THRESHOLD. The fan will stay on until the temperature drops below the threshold - TEMP_HYST. This way the fan doesn't rapidly turn on and off when the room is around the temperature threshold.

 

                    import RPi.GPIO as GPIO
import smbus
import time
#0 = /dev/i2c-0
#1 = /dev/i2c-1
I2C_BUS = 0
bus = smbus.SMBus(I2C_BUS)
    
#7 bit address (will be left shifted to add the read write bit)
DEVICE_ADDRESS = 0x48      
TEMP_THRESHOLD = 78
TEMP_HYST = 2

GPIO.setwarnings(False)
GPIO.setmode(GPIO.BCM)
FAN_PIN = 23
GPIO.setup(FAN_PIN, GPIO.OUT)

while True:
	time.sleep(1)
	#Read the temp register
	temp_reg_12bit = bus.read_word_data(DEVICE_ADDRESS , 0 )
	temp_low = (temp_reg_12bit & 0xff00) >> 8
	temp_high = (temp_reg_12bit & 0x00ff)
	#convert to temp from page 6 of datasheet
	temp  = ((( temp_high * 256 ) + temp_low) >> 4 )
	#handle negative temps
	if temp > 0x7FF:
		temp = temp-4096;
	temp_C = float(temp) * 0.0625
	temp_F = temp_C * 9/5+32
	print "Temp = %3.1f C -- %3.1f F" % (temp_C,temp_F)

	#control the fan based on the temp
	if(temp_F > TEMP_THRESHOLD):
		GPIO.output(FAN_PIN, True)
	if(temp_F < (TEMP_THRESHOLD - TEMP_HYST)):
		GPIO.output(FAN_PIN, False) 
516 likes
Statement: This post is only the personal view of the author and does not represent the opinions of ALLPCB.com.

Chicken Hacker

Leave A Message

Follow

Good resource for new beginners.
ThreadReply