Power Supply Prob.

Discussion in 'General Electronics Chat' started by m4ch1n314ngu4g3, Dec 14, 2013.

  1. gootee

    Senior Member

    Apr 24, 2007
    447
    51
    Try a heavier power supply.

    Also, if you are not using decoupling and bypass capacitors, that will be a significant problem.

    Surely you have a small bypass cap for each chip's power connection. But then you also need to scatter electrolytic caps around your circuit. A 10uF for each chip would be good but you might get away with fewer.

    Each breadboard should also have at least 100uF where the power enters the board.

    And any centralized power distribution point should have some significant capacitance, too, especially if it's more than a few inches from the psu.

    I hope you're not going to try to run this at any high speed.
     
  2. m4ch1n314ngu4g3

    Thread Starter New Member

    Aug 20, 2013
    27
    1
    Hmm, well the maximum clock rate will be 16 MHz but the only chips that it will be affecting are the main program counters and the frequency divider binary counter chip, which in turn will all output an 8 MHz frequency of the least significant bit. There will be some long wires that carry these signals to the inputs of some 74LS126 buffers that invoke the timing for the storage and latching of data into the 74HC574 registers.

    Other than that, the most common frequencies will be at 8 MHz and I am thinking of using bypass capacitors after I have completed the low speed 1 Hz to 4 Hz testing and have continued onto running at full speed.

    Others said that .1 uF per chip is enough, but 10 uF is a hundred times that. You basically told me to use 10 to 100 times the capacitance of what I was previously told; .1 uF per chip, 10 uF per board, and maybe 100 uF at major points. Is there any specific significance when using these capacitances between 8 to 16 MHz?
     
  3. antonv

    Active Member

    Nov 27, 2012
    148
    26
    You shouldn't need more than 0.1uF per chip plus an electrolytic per module as has been suggested.

    Before putting regulators everywhere, try redoing your star wiring: make the star by soldering a pair of wires for each module to the wires coming from the power supply. Don't rely on breadboard to make this connection. The only wires plugged into the breadboard should be the final connections to each module.
     
  4. m4ch1n314ngu4g3

    Thread Starter New Member

    Aug 20, 2013
    27
    1
    Yeah, I bought a small prototyping board and plan on soldering the power adapter to it while making a set of soldering connections from which to do all the star connections. Power supply -> Power adapter on Prototype board -> Soldered power bus on Prototype board -> Wires -> individual bread boards. So yeah, the only breadboard connections are the ones to each individual breadboard or module as you have said.

    And if I were to use the power (voltage) regulators, would it work if I only used seven 7805 chips, one for each row of boards, and solder them to the prototyping board? I believe that logically they should each only be driving approximately one seventh (1/7) of the total current depending on the chips that are located on that row of breadboards. I'd rather do that as 21 7805s is a lot and I don't have much space on the board as well as on the prototyping board.
     
  5. antonv

    Active Member

    Nov 27, 2012
    148
    26
    7 should be fine. They may need heat sinks though.
     
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