Vcc ~ ground -=|

Discussion in 'The Projects Forum' started by tech5563, Oct 29, 2010.

  1. tech5563

    Thread Starter New Member

    Sep 30, 2010
    totaly of the wall noob question here :s

    on most of the schematics i have seen here and on software circuit test programs. why do they not show where you have to connect the vcc or ground pins of an ic chip like the 4017 or 74hc163 etc.?.

    are we to assume that say pin 16 goes to the + and say pin 7 to goes to ground on all designs.?.

    or is it that all pins that are not shown in a schematic means its unused?

    sorry i maybe a pc tech of over 30 years but now getting into electronics
    i must say i feel like little worm on a very big hook in a very deep ocean lol soz
  2. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    I don't know what programs you have used. I do have experience with EAGLE. You can show the power pins, if you want to by using the invoke button. However, having the power pins separate can make make reading the schematic easier as it is less cluttered. The power pins are then handled separately.

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  3. beenthere

    Retired Moderator

    Apr 20, 2004
    That is almost always the case. But there are ICs that use other pins for Vcc & ground. The best bet is to get the data sheet for the logic IC to resolve all questions.
    tech5563 likes this.
  4. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    Yes on most schematics the ground and power pins will be assumed to hooked to power distribution busses, or will be shown as a series of numbered pins and power lines all connected, but located in a corner of the drawing, or on a second page, removed from the actual drawings of those devices elsewhere in the circuit.
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  5. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    MultiSim does this as well, when you choose a gate, it labels them A-D or A-F in the case of a Hex inverter.

    Then just the logic symbols are put on the schematic. As long as there is logic 5V and GND on the same schematic, it uses them for the power. If you build a circuit board from the schematic, you need to remember to add power runs if not using the multisim board routing.
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  6. themindflayer


    Oct 29, 2010
    some ics are multiple packages built into a single IC like the 7408 (Quad 2 i/p and gate) and such circuits are easier to understand if we use logic gate symbol of the 'and' gate so designers prefer the ic broken into its components .. another advantage is that this also makes it easier for placing each gate where req in the schematic and labelled as U1A, U1B, U1C and U1D .... and since each 'and' gate uses the same power supply pins it is better to show them once than with each gate again and again.... or even better not show them at all ....
    tech5563 likes this.
  7. tech5563

    Thread Starter New Member

    Sep 30, 2010
    Thankyou all so much for your help i really appreciate it :D
  8. SgtWookie


    Jul 17, 2007
    There is no "hard and fast" rule about which pins get Vcc/Vdd/GND/Vee/Vss applied to them. Unless you like smoke, look up the datasheet for the IC in question.

    Something else that will "bite" you is that besides not showing the Vcc/Vdd/GND/Vee/Vss pins on schematics, they won't show the supply bypass capacitors.

    Virtually any IC, whether digital or analog, requires at a minimum of an 0.1uF/100nF metal poly film or ceramic cap connected from GND to each power supply "rail" pin.

    Some, notably the 555 timer and variants, require more than one supply bypass capacitor. You have to look at the datasheet for the particular IC being used to be certain of the requirements.

    If you omit the required bypass capacitor(s), you WILL have problems.