I was building a logic circuitry that performs 8 bit multiplier 16 bit divider using decoders as finite state machine in breadboards. the circuit is a bit large and i wonder why grounds or low voltage doesn't spread to other part of the circuitry or ICs. When test with logic probe, the reading has noise and most of the time, there will be no reading.

I come to a point to try to short VCC and ground. This solves everything. The circuitry has grounds to the whole circuit or to all ICs. And also, LEDs have high brightness.

My question is in large circuits, why does ground not spread evenly to other ICs or other parts of the circuit? and What is the explanation of the ground and VCC shorting solve this problem?

  • 3
    \$\begingroup\$ Show a picture of your breadboard, indicating where you are "shorting Vcc and Ground". Note that on many plastic breadboards, the Vcc and Ground rails along the sides of the breadboard are broken in the middle of the board. \$\endgroup\$ – Peter Bennett Apr 3 '16 at 23:58

It sounds like you had a mechanical issue with poor connections, which was temporarily cured by a bit of arc welding. I doubt anything electronic occurred, you just got some weird lucky break. Normally shorting Vcc and ground will explode, destruct or evaporate the weakest link in the Vcc and ground wiring between the short and the power supply.

On an overcurrent-protected power supply, shorting Vcc and ground will cause the power supply to crowbar, i.e. Shut off and re-energize, effectively rebooting the circuit. While also, obviously, draining any capacitance between Vcc and ground. So it does affect the circuit,

  • \$\begingroup\$ But, i am also doing that solution for my other large circuitry such as demultiplexer input and output circuitry. It just solves the problem. I think its not luck. THeres gotta be an explanation for that. Because if i lift up the gnd wire before the connection of the IC's ground pin then i test the wire with logic probe, there is a reading of gnd. \$\endgroup\$ – Karl Kangleon Apr 3 '16 at 23:43
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    \$\begingroup\$ Shorting Vcc and ground is never a proper solution to any problem. Unless the problem is "testing the power supply's overcurrent protection". If you don't know why it solves the problem, it's the very definition of luck. \$\endgroup\$ – Harper - Reinstate Monica Apr 4 '16 at 0:23

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