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Discussion in 'General Electronics Discussion' started by digital96, Nov 11, 2012.

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  1. digital96

    digital96

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    Nov 11, 2012
    Hello. I'm new to this forum and to electronics, but a few days ago I ordered some digital integrated circuits from NTE through Radio Shack's website. (An NTE4071B, an NTE4013B, and an NTE4516B.) When I got my order, I took the chips to my room where I had all my other electronics stuff and made a simple test circuit on my breadboard. There were stickers on the packets saying that they were sensitive to static electricity, but at some times, the LED for the output would turn on when I got my hand anywhere near the circuit. I thought that maybe it was the carpet in my room, so I moved everything to the basement. But still it kept happening. I even tried using long wires to get the switches away from the circuit, but since there was metal on them, now the LED would also turn on if I got my hand near the switches. I've tried to discharge myself by touching metal before using the electronics, but no help. In all the time I spent looking for answers on the internet I've never seen anyone else have these issues. Please tell me if you know how to fix this.
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    11,522
    2,654
    Nov 17, 2011
    These are CMOS ics. CMOS has a very high input impedance (MegOhms). You should always tie unused inputs to a defined logic level by using either pull-up or pull-down resistors. Never leave CMOS inputs open. They will catch any static electricity and cause the gates to go haywire.

    That's what you're seing.

    In fact, I employed this behaviour on purpose many years ago for a small gimmick: A box containing to AAA batteries, a 4 gate CMOS ic and an LED. Whenever someone came near to the box the LED would light.

    But that's not what you want in an orderly circuit.

    Harald
     
  3. digital96

    digital96

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    Nov 11, 2012
    Thanks a lot! The chips are working normally now.
     
  4. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    They were working normally before, as well :D

    Bob
     
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