Low voltage on header pin

[Jadams]

One of my Prop 1 sensor applications stopped working after 6 months.  I found that the center header pins (red) only has 3.8V.  All 7 pins are the same.  There is 12V on the supply side of the voltage regulator and 5.05V on the regulated side.  In switch position #2 there is 12V at V+.  Trash it?

[JonnyMac]

Disconnect everything except the power supply and check again.  I'm curious as to how you're finding 5.05 on the output of the regulator and only 3.8v on the R pins as they are directly connected.  The only way to get a clean reading is with everything (that could cause a load) disconnected.

[bsnut]

I am in agreement with Jon on this. What you had connected could've caused the voltage regulator to shut down. I found the same problem when I short out a plug-in power supply.

[Jadams]

I had it disconnected when I tested it.  This time I connected the meter to pin0 (red), on the header, grounded it on the screw on the voltage regulator and turned on the power.  It took about 30 seconds to ramp up to 3.5V.  It started at 1.1 and steadily moved up to 3.5.  Could it be a bad capacitor?  I again check both sides of the regulator 12V and 5.05.

[JonnyMac]

I'm still having a hard time with this.  If you flip the board over you'll see a big fat trace from the output of the regulator directly to the R pins of the header. One fat trace and one medium trace route to the big caps we put on the board to help when servos are connected.  My point is there is such a low-Z connection to the output of the regulator that what you see there you should see on the R pins and vice-versa.

Now... don't chuck the board.  Call John B (916-770-9244) and get an RMA so you can send it him; I'm sure it's fixable.

[Jadams]

Thanks, I'll call him tomorrow.

[JackMan]

Was this Prop-1 in an area for 6 months that could have caused corrosion? Corrosion on the pins (and this is a long shot) is about the only thing that I can think of that could possibly cause the situation you are describing. As Jon said, the R pins are directly connected to the 5v side of the regulator, 5v at the regulator should be 5v at the R pins.

[Jadams]

No, this prop was located inside my shop running the following program that JohnnyMac wrote for me in a thread on August9, 2010 titled 'Debounce PIR'.  I have looked at the wiring to see if something has shorted or opened, but can't find a problem.  I have installed a new prop and cannot make if function as before.  The red light stays on all the time.  I'm not going to connect until I find the issue.  Here is the program, and thank you for inquiring about the problem:


' =========================================================================
'
'   File......
'   Purpose...
'   Author....
'   E-mail....
'   Started...
'   Updated...
'
'   {$STAMP BS1}
'   {$PBASIC 1.0}
'
' =========================================================================


' -----[ Program Description ]---------------------------------------------
'
' P6 : Connect NC contacts between P6.W and P6.B; when relay is active and
'      contacts open, P6 goes high.
'
' P5 : Configure photoresistor circuit so that input goes high when dark
'
'      +5 ---[fixed]--- P5.W ---[photoresistor]--- P5.B
'
' Remove ULN2803 pins 1, 2, and 3.


' -----[ Revision History ]------------------------------------------------


' -----[ I/O Definitions ]-------------------------------------------------

SYMBOL  PIR             = PIN7                  ' SETUP = UP; no ULN

SYMBOL  LightBeam       = PIN6                  ' SETUP = UP; no ULN
SYMBOL  Darkness        = PIN5                  ' no ULN
SYMBOL  Sounder         = PIN4                  ' piezo transducer

SYMBOL  Green           = PIN3                  ' green led
SYMBOL  Red             = PIN2                  ' red led
SYMBOL  Yellow          = PIN1                  ' yellow led
SYMBOL  Lights          = PIN0                  ' relay for 120v lights


' -----[ Constants ]-------------------------------------------------------

SYMBOL  IsOn            = 1                     ' for active-high in/out
SYMBOL  IsOff           = 0

SYMBOL  Yes             = 1                     ' for active-high in/out
SYMBOL  No              = 0

SYMBOL  Baud            = OT2400


' -----[ Variables ]-------------------------------------------------------

SYMBOL  triggers        = B0
SYMBOL   trPIR          =  BIT7
SYMBOL   trBeam         =  BIT6                 ' debounced trigger bits
SYMBOL   trDark         =  BIT5


SYMBOL  status          = B1
SYMBOL   playing        =  BIT15

SYMBOL  idx             = B2


' -----[ Initialization ]--------------------------------------------------

Power_Up:
  PINS = %00000000                              ' clear all
  DIRS = %00011111                              ' make P0-P3 outputs

  PAUSE 100000                                  ' PIR warm-up

Reset:
  PAUSE 5000                                   ' re-trigger delay


' -----[ Program Code ]----------------------------------------------------

Main:
  triggers = %11100000                          ' arm triggers
  FOR idx = 1 TO 20                             ' debounce, 100ms
    PAUSE 5
    triggers = triggers & PINS                  ' re-scan inputs
  NEXT

  Red = trDark                                  ' if dark, Red is on

  IF trBeam = Yes THEN Show_Y                   ' beam broken?
  IF trPIR = Yes THEN Show_G                    ' PIR detect?
  GOTO Main


Show_Y:

    FOR idx = 1 TO 5                             ' flash
    Sounder = Ison
    Yellow = IsOn
    PAUSE 250
    Sounder = Isoff
    Yellow = IsOff
    PAUSE 250
  NEXT



  IF Darkness = No THEN Main
  Lights = IsOn                                 ' 120v lights on
  PAUSE 20000
  Lights = IsOff

  GOTO Main


Show_G:

   FOR idx = 1 TO 10                             ' flash
    Sounder = Ison
    Green = IsOn
    PAUSE 150
    Sounder = Isoff
    Green = IsOff
    PAUSE 150
  NEXT
    PAUSE 250



  GOTO Reset


' -----[ Subroutines ]-----------------------------------------------------



' -------------------------------------------------------------------------



' -----[ User Data ]-------------------------------------------------------

[bsnut]

I'm still having a hard time with this too ???. Did you have your wiring (PIR and photoresistor) disconnected from the Prop-1, but the power supply and you had 5v at the "R" pins and at the voltage regulator?

When a voltage regulator is shorted, I have seen goofy voltages like what you are seeing. When you remove power from the regulator it resets itself. I agree with Jon on the low-Z connection thinking.     

[Jadams]

Got it.  You were right about maybe corrosion or a connection issue.  I soldered a wire from the 5V leg of the regulator to the +side of the cap located near the header pins, it's not pretty, but it works.  I'm not sure which joint caused the problem, but anyway, I'm back in business.  Thanks for all your help.  You saved me 40 bucks or so. 

[JackMan]

I'm glad you're back in business but that still doesn't make sense. Those 470uF caps are nothing but storage tanks, with no load you should have 5v at the R pins with or without those caps.

[bsnut]

I am glad you got working. Now, you know where your problem is located. The answer is, what cause the problem, the caps or something else.

One way to find out if the caps were the cause is to unsoldered the caps on 5v side to see if any of them are bad with an multimeter set on "CAP". If you chose to do it this, you can also check the traces with an multimeter set on "OHMS" where the caps were soldered leakage of voltage between the traces . Remember to remove caps before checking, so you don't get any goofy readings.

[Jadams]

I don't think the problem is in the caps.  When I soldered the wire from the regulator to the + side of the cap near the header pins, I, in effect, replaced the big fat trace to the header pins.  So the issue may have been the solder connection between the +5 on the regulator and the trace.  I have never been successful at soldering on the trace.  I'm sure there is a trick to it but I'm not very good at soldering.  So far it's working and I appreciate the help and advice.

[JonnyMac]

There may have been an iffy solder connection from the output of the regulator to the supply trace.  This is unusual as the boards are machine soldered, but there may have been corrosion on the part going into the board.  What you may have done in your resolder process is fix that joint. 

Note that when I build my own circuits using any TO-220 part I clean the legs with steel wool before soldering into the board.