How stable would this be as a no hardware distance sensor?

I was writing and testing some code for a project I have in Customer Projects, when I noticed that each time I placed my hand within 1.5 to 2 inches it would be detected by a hanging wire connected to a propeller pin. I have I2C code running on the pin next to it so I am curious if it is creating capacitance...

Here is the code I was working on
{{

  HC-SR04 Trigger Driver
  8x HC-SR04 are used
  All Trig pins are connected to the MCP23017 on seperate lines
  All echo pins are tied together and connected to the Propeller

  Only one HC-SR04 is read at a time clockwise from Left of the
  robot device

  License: MIT

    Copyright (c) 2011-2018 Jorge Joaquin Pareja

    Permission is hereby granted, free of charge, to any person obtaining a
    copy of this software and associated documentation files (the
    "Software"), to deal in the Software without restriction, including
    without limitation the rights to use, copy, modify, merge, publish,
    distribute, sublicense, and/or sell copies of the Software, and to
    permit persons to whom the Software is furnished to do so, subject
    to the following conditions:

    The above copyright notice and this permission notice shall be included
    in all copies or substantial portions of the Software.

    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
    OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
    MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
    IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
    CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
    TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
    SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE


}}


CON
        _clkmode = xtal1 + pll16x                                               'Standard clock mode * crystal frequency = 80 MHz
        _xinfreq = 5_000_000

        ' Connect up to 16 trigger pins to the MCP23017
        ' Connect all echo pins together and connect them to a free Propeller pin and define that pin as ECHO below
        
        SDA = 0      ' Prop pin 0
        SCL = 1      ' Prop pin 1

        ECHO = 2
        
                          'Hardware addressable pins 15, 16, and 17
                          '|||
        MCPADDR    = %0100_000 ' leave off the R/W bit, Address is shifted right to put the bit in by the driver

        INPUT_BIT  = %1
        OUTPUT_BIT = %0
        
        ALLOUTPUT     = %0000_0000
        ALLINPUT      = %1111_1111

        ALLOFF    = %0000_0000

        TRIG_0    = %0000_0001  ' Left Center  GPA0
        TRIG_1    = %0000_0010  ' Left Front   GPA1
        TRIG_2    = %0000_0100  ' Front Center GPA2
        TRIG_3    = %0000_1000  ' Right Front  GPA3
        TRIG_4    = %0001_0000  ' Right Center GPA4
        TRIG_5    = %0010_0000  ' Right Rear   GPA5
        TRIG_6    = %0100_0000  ' Rear Center  GPA6
        TRIG_7    = %1000_0000  ' Left Rear    GPA7
        TRIG_8    = %0000_0001  ' spare
        TRIG_9    = %0000_0010  ' spare
        TRIG_10   = %0000_0100  ' spare
        TRIG_11   = %0000_1000  ' spare
        TRIG_12   = %0001_0000  ' spare
        TRIG_13   = %0010_0000  ' spare
        TRIG_14   = %0100_0000  ' spare
        TRIG_15   = %1000_0000  ' spare
        
        ' MCP CONFIG Registers ICON.BANK = 0
        IODIRA    = $00
        IODIRB    = $01
        IPOLA     = $02
        IPOLB     = $03
        GPINTENA  = $04
        GPINTENB  = $05
        DEFVALA   = $06
        DEFVALB   = $07
        INTCONA   = $08
        INTCONB   = $09
        IOCON     = $0A

        GPPUA     = $0C
        GPPUB     = $0D
        INTFA     = $0E
        INTFB     = $0F
        INTCAPA   = $10
        INTCAPB   = $11
        GPIOA     = $12
        GPIOB     = $13
        OLATA     = $14
        OLATB     = $15

        ' from Timing.spin
        _10us = 1_000_000 /        10                         ' Divisor for 10 us
        _1ms  = 1_000_000 /     1_000                         ' Divisor for 1 ms
        _1s   = 1_000_000 / 1_000_000                         ' Divisor for 1 s

        DEBUG = 1
        
VAR
        LONG clkcycles ' 
   
OBJ
  mcp      : "i2cDriver.spin"
  pst      : "Parallax Serial Terminal.spin" ' only use for debugging or it slows us down
  
PUB MAIN | tmp, pass
    ' init pst
    pst.Start(115200)
    mcp.Init(SCL, SDA)

    MCP_Config

    pass := 1
    tmp := 0

    REPEAT
      USS_Read(tmp)
      tmp++
      IF tmp == 16
        tmp := 0
        pst.Clear
        pst.Str(STRING("Pass: "))
        pst.Dec(pass)
        pst.NewLine
        pass++

PUB MCP_Config
    ' set all pins to output
    MCP_Write(IODIRA, ALLOUTPUT)
    MCP_Write(IODIRB, ALLOUTPUT)

    MCP_Write(GPIOA, %0000_0000)
    MCP_Write(GPIOB, %0000_0000)

PUB USS_Read(device) | cnt1, cnt2, Microseconds, Distance
    CASE device
      0:
        MCP_PinGPB(ALLOFF)
        MCP_PinGPA(TRIG_0)
        WaitUsec10
        MCP_PinGPA(ALLOFF)
      1:
        MCP_PinGPB(ALLOFF)
        MCP_PinGPA(TRIG_1)
        WaitUsec10
        MCP_PinGPA(ALLOFF)
      2:
        MCP_PinGPB(ALLOFF)
        MCP_PinGPA(TRIG_2)
        WaitUsec10
        MCP_PinGPA(ALLOFF)
      3:
        MCP_PinGPB(ALLOFF)
        MCP_PinGPA(TRIG_3)
        WaitUsec10
        MCP_PinGPA(ALLOFF)
      4:
        MCP_PinGPB(ALLOFF)
        MCP_PinGPA(TRIG_4)
        WaitUsec10
        MCP_PinGPA(ALLOFF)
      5:
        MCP_PinGPB(ALLOFF)
        MCP_PinGPA(TRIG_5)
        WaitUsec10
        MCP_PinGPA(ALLOFF)
      6:
        MCP_PinGPB(ALLOFF)
        MCP_PinGPA(TRIG_6)
        WaitUsec10
        MCP_PinGPA(ALLOFF)
      7:
        MCP_PinGPB(ALLOFF)
        MCP_PinGPA(TRIG_7)
        WaitUsec10
        MCP_PinGPA(ALLOFF)
      8:
        MCP_PinGPA(ALLOFF)
        MCP_PinGPB(TRIG_8)
        WaitUsec10
        MCP_PinGPB(ALLOFF)
      9:
        MCP_PinGPA(ALLOFF)
        MCP_PinGPB(TRIG_9)
        WaitUsec10
        MCP_PinGPB(ALLOFF)
      10:
        MCP_PinGPA(ALLOFF)
        MCP_PinGPB(TRIG_10)
        WaitUsec10
        MCP_PinGPB(ALLOFF)
      11:
        MCP_PinGPA(ALLOFF)
        MCP_PinGPB(TRIG_11)
        WaitUsec10
        MCP_PinGPB(ALLOFF)
      12:
        MCP_PinGPA(ALLOFF)
        MCP_PinGPB(TRIG_12)
        WaitUsec10
        MCP_PinGPB(ALLOFF)
      13:
        MCP_PinGPA(ALLOFF)
        MCP_PinGPB(TRIG_13)
        WaitUsec10
        MCP_PinGPB(ALLOFF)
      14:
        MCP_PinGPA(ALLOFF)
        MCP_PinGPB(TRIG_14)
        WaitUsec10
        MCP_PinGPB(ALLOFF)
      15:
        MCP_PinGPA(ALLOFF)
        MCP_PinGPB(TRIG_15)
        WaitUsec10
        MCP_PinGPB(ALLOFF)

    ' Start reading
    WAITPNE(0, |< ECHO, 0)
      cnt1 := CNT
      WAITPEQ(0, |< ECHO, 0)
      cnt2 := CNT
      Microseconds := (||(cnt1 - cnt2) / (CLKFREQ / 1_000_000)) >> 1
      if DEBUG == 1
        pst.Home
        pst.ClearEnd
        pst.Dec(Microseconds)
        pst.Str(STRING(" us. "))
      Distance := Millimeters(Microseconds)

      IF DEBUG == 1
        pst.Dec(Distance)
        pst.Str(STRING(" mm."))

      pause1ms(100)

'From Timing.spin
PUB pause1ms(period)
    '' Pause execution for period (in units of 1 ms).
    clkcycles := ((CLKFREQ / _1ms * period) - 4296) #> 381     ' Calculate 1 ms time unit
    WAITCNT(clkcycles + CNT)                                   ' Wait for designated time

PUB Millimeters(ms) : Distance                                                  
''Measure object distance in millimeters
                                              
  Distance := ms * 10_000 / TO_CM                                       ' Distance In Millimeters


PUB WaitUsec10
    WAITCNT ((mcp#uSec * 10) + cnt)
      

PUB MCP_PinGPA(data)
    mcp.WriteByteA8(MCPADDR, GPIOA, data)

PUB MCP_PinGPB(data)
    mcp.WriteByteA8(MCPADDR, GPIOB, data)    

PUB MCP_Write(reg, data)
    mcp.WriteByteA8(MCPADDR, reg, data)

DAT
        TO_CM         LONG      29_386 

I have never noticed this with the Propeller before.
Can an anomaly like this be relied upon to work all the time?


Here is a video showing it:


Jorge P.

Comments

  • 5 Comments sorted by Date Added Votes
  • I came across http://www.ti.com/lit/an/snoa928a/snoa928a.pdf some time ago - it may be relevant to you.

    Mike R...
  • JonnyMacJonnyMac Posts: 6,090
    edited May 29 Vote Up0Vote Down
    As you know, breadboards are like a bunch capacitors and can be problematic in development. I've used the MCP23017 in a few commercial apps with proper PCBs without any problems; one of them was a networked HVAC system that used the MCP23017 to provide chips select signals to a large array of sensors -- similar to what you're doing.

    I've attached my MCP23017 object in case you'd like to compare code.
    Jon McPhalen
    Hollywood, CA
    It's Jon or JonnyMac -- please do not call me Jonny.
  • JonnyMac wrote: »
    I've attached my MCP23017 object in case you'd like to compare code.

    The I2C driver is based off your code, modified by Erlend Fj. Your included zip seems newer so I'll give it a try.
    Jorge P.
  • That is a nice demonstration that our electronic circuits are not just a collections of components that do whatever they do connected by wires that do nothing except connect those components together electrically. The so called "lumped circuit model".

    No, our circuits are a big wobbly jelly of electric and magnetic fields that allow every part to interact with every other, including parts that we don't think of as being in the circuit, like your hand. In ways that are often difficult to fathom. Ping on one part of that jelly and all the other parts quiver.
  • kwinnkwinn Posts: 7,963
    That is probably caused by the signal your body is picking up from the 50/60Hz AC lines all around you. A fairly common phenomenon when using prototyping boards and point to point wiring with chips that have very high input impedances.
    In science there is no authority. There is only experiment.
    Life is unpredictable. Eat dessert first.
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