Author Topic: What could cause dc voltage on non-connected pins?  (Read 1133 times)

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Offline Andy-In_over_my_headTopic starter

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What could cause dc voltage on non-connected pins?
« on: January 05, 2018, 04:53:41 am »
So I made a little board for playing with 8 pin chips that have power top right and ground bottom left. I’m powered with 7805 to top right pin and the 3 pins below that are solo. However, I have 5v on pin 8, 2.73v on pin 7, 1.075v on pin 6 and .540v on pin 5. Nothing on ground or 2-4. Could flux residue carry voltage? I cleaned most off so I’m confused what is causing this.
Thanks in advance for the help!
"I'd rather be buried then ungrateful to be given life and food on the table. And in a world this shaky and unstable, we've got to be less hateful!"
 

Offline Peabody

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Re: What could cause dc voltage on non-connected pins?
« Reply #1 on: January 05, 2018, 05:02:50 am »
Not sure what you mean by top right and bottom left.  But the voltage that may be present on any pin could result from normal connections inside the chip.  If you would tell us which 8-pin chip you have, perhaps someone who also has that chip could see if he gets the same readings. 
 

Offline Richard Crowley

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Re: What could cause dc voltage on non-connected pins?
« Reply #2 on: January 05, 2018, 05:14:48 am »
Please learn how to identify the pins by number. "Top right" and "bottom left" mean nothing without proper context.
Note also that all 8-pin chips are NOT all the same.  So, a generic question like this is not valid.
As @Peabody mentioned, what you are seeing is quite normal because of the circuitry inside your (unidentified) chip.
 
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Offline Andy-In_over_my_headTopic starter

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Re: What could cause dc voltage on non-connected pins?
« Reply #4 on: January 05, 2018, 07:04:30 am »
 I think I wrote this wrong. There’s no chip. There’s no specific PIN numbers but if I had to use pins, an example would attiny85 with Vcc as pin 8 and ground as pin 4. Pin 8-7 has 5 megs resistance, 8-6 = 10 meg, 8-5 = 22 meg. I get the voltages but why? I put my BK precision 879B probes into the flux I have and got no resistance at any distance from each other. So on basic perf board, what am I missing?
And I’m sorry if I can’t type out the perfect explanation. I posted in a beginner section with a beginner problem. I know enough to get by with my own projects but just haven’t had this particular problem before. I think I made this confusing by not being forward saying there’s not chip on this board. A 7805 to put power and ground to opposite corners on an empty 8 pin socket.
"I'd rather be buried then ungrateful to be given life and food on the table. And in a world this shaky and unstable, we've got to be less hateful!"
 

Offline Andy-In_over_my_headTopic starter

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Re: What could cause dc voltage on non-connected pins?
« Reply #5 on: January 05, 2018, 07:07:33 am »
Okay. I understand then. I moved to Hawaii this pst year and it’s very humid. So after I get the flux super hot and with the humidity it’s became conductive. Makes sense why I get no resistances putting the leads into the flux.
"I'd rather be buried then ungrateful to be given life and food on the table. And in a world this shaky and unstable, we've got to be less hateful!"
 


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