Overview
My background is pure software. To be able to manipulate the virtual world (software) using the physical world (hardware), for me is exciting and new. I wanted to share my experiences and get some feedback.
Goal
Manipulate relays using buttons.
Button 1 - activates relay 6
Button 2 - activates relay 7
Button 3 - deactivates all relays
Button 1 - activates relay 6
Button 2 - activates relay 7
Button 3 - deactivates all relays
Preparing your Raspberry Pi
Schematic
For the sake of simplicity of the diagram I used LEDs, but my actual circuit used an 8 channel relay module where channel 6 and 7 are connected in place of the LEDs.
Script
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| #!/usr/bin/python | |
| import smbus | |
| import sys | |
| import time | |
| bus = smbus.SMBus(1) | |
| address = 0x20 | |
| bus.write_byte_data(address,0x00,0x00) # set A7-A0 as output pins | |
| bus.write_byte_data(address,0x01,0x07) # set B0-B3 as input pins , B4-7 as output 0000111 | |
| bankA=0x12 | |
| bankB=0x13 | |
| def main(): | |
| a = 0 | |
| b = 0 | |
| inp = 0 | |
| delay = 0.05 | |
| #Turnoff all outputs in bank A | |
| a = 255 # 11111111 | |
| bus.write_byte_data(address,bankA,a) | |
| #Reset all buttons | |
| #you need to bring them up using a 10KOhm resistor connected to 3.3v | |
| #You can't just do the following using code and expect it to be stable | |
| #If you do the following without the 3.3v it will be unpredictable. | |
| b = 255 # 11111111 | |
| bus.write_byte_data(address,bankB,b) | |
| while True: | |
| # read input from bank B and store to "inp" variable | |
| inp = bus.read_byte_data(address,bankB) | |
| #Check if button B0 is pressed, light relay A6 | |
| if inp == 254: # 11111110 (B0) | |
| #print "B7" | |
| bus.write_byte_data(address,bankA,191) #light relay A6 10111111 | |
| #Check if button B1 is pressed, light relay A7 | |
| if inp == 253: # 11111101 (B1) | |
| #print "B6" | |
| bus.write_byte_data(address,bankA,127) #light relay A7 01111111 | |
| #Check if button B2 is pressed, light relay A6 | |
| if inp == 251: # 11111011 (B2) | |
| #print "B5" | |
| bus.write_byte_data(address,bankA,255) #turn off all relay A7 11111111 | |
| time.sleep(delay) | |
| print str(inp) | |
| if __name__ == "__main__": | |
| main() | |
