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Legacy Personal Blogs And then there were bumpers - don't forget the pull-ups!
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  • Author Author: alanmcdonley
  • Date Created: 10 Jun 2016 11:58 AM Date Created
  • Views 321 views
  • Likes 1 like
  • Comments 1 comment
  • negative_logic
  • python
  • robot
  • catching_control_c
  • mcp23s17
  • bumpers
Related
Recommended

And then there were bumpers - don't forget the pull-ups!

alanmcdonley
alanmcdonley
10 Jun 2016
I feel so elated to report I figured out my bumper problem. I had designed the connections to be active low using the internal pull-ups of the MCP23S17 but forgot this during my time away from my bot.

 

I used the (private/unsupported) PDALib.setDioBit(reg, pin) function to set the pull-ups and voila - I've got three working negative logic bumpers (rear, left, right). With the skirt on, this gives the bot 6 usable bump directions:

 

    • front (left + right)
    • left (and left front)
    • right (and right front)
    • left rear (left+rear)
    • right rear (right+rear)
    • rear
and "I'm in real trouble" (left+right+rear)

(The Pi Droid Alpha interface board maps the MCP23S17 DIO Bank A to be DIO 8-15, so Bank A Bits 0,1,2 are channel 8, 9, 10 in the program)

 

https://flic.kr/p/xxU7Hr

Here is my program:
# ############################# BUMPER TEST ################
import PDALib
import time
import sys
import signal

# ################# BUMPER TEST ###########

# Bumpers are on
# DIO 10   Left Front
# DIO 9      Right Front
# DIO 8      Rear
# Wired to use internal pull-ups of the MCP23S17
# Bumper value is negative logic - 0 means bumper activated, normal 1

# Encoders are on DIO 11 and 12

# ##################
# Callback and setup to catch control-C and quit program
def signal_handler(signal, frame):
  print '\n** Control-C Detected'
  PDALib.LibExit()
  sys.exit(0)

# Setup the callback to catch control-C
signal.signal(signal.SIGINT, signal_handler)
# ##################

# Set up all DIO channels as input for now
for pin in range(8,23+1):
  PDALib.pinMode(pin,PDALib.INPUT)

# Set internal pull-ups on bumper channels
PDALib.setDioBit( PDALib.DIO_GPPU, 0 )  # set pin 8 pull-up
PDALib.setDioBit( PDALib.DIO_GPPU, 1 )  # set pin 9 pull-up
PDALib.setDioBit( PDALib.DIO_GPPU, 2 )  # set pin 10 pull-up

# Loop displaying bumpers and encoders
while True:
  for pin in range(8,12+1):
    print "Pin:", pin, PDALib.digitalRead(pin)
  print "\n"
  time.sleep(1)
#end while
http://forums.mikronauts.com/viewtopic.php?f=49&t=63&p=250#wrap
  • Sign in to reply
  • DAB
    DAB over 8 years ago

    Yes, good making involves understanding the hardware and the software.

     

    Without pull up or pull down resisters you can have floating inputs, which can introduce a lot of very nasty signals and potentially kill the chip.

     

    This issue was very critical for some of the old CMOS chips.   ESD would kill them in femtoseconds.

     

    DAB

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