Shop OBEX P1 Docs P2 Docs Learn Events
Supply Bypass Cap on Proto Board — Parallax Forums

Supply Bypass Cap on Proto Board

Ken PetersonKen Peterson Posts: 806
edited 2007-10-10 20:25 in Propeller 1
Anybody know what type of bypass cap is being used on the proto board?· We had a serious noise problem on a project we're working on in the 60 MHz range at about 150mV p-p.· We added a 0.1uF ceramic in parallel to the 1uF that is already on the board and it killed the noise.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔


The more I know, the more I know I don't know.· Is this what they call Wisdom?

Comments

  • Graham StablerGraham Stabler Posts: 2,510
    edited 2007-10-09 21:02
    They all look ceramic to me.

    Graham
  • deSilvadeSilva Posts: 2,967
    edited 2007-10-09 21:43
    The diagram in the protoboard description shows a 1uF electrolyte, most likely a tantal cap.... (I have mislaid my protoboard at the moment... maybe it's in the office..)
  • Graham StablerGraham Stabler Posts: 2,510
    edited 2007-10-09 22:45
    The diagram does indeed show an polarized cap but the only one on the board is the 1000uF electroltyic. The capacitor connected to vdd/vss is not polarized and looks just like a small ceramic, no markings at all.

    Graham
  • Ken PetersonKen Peterson Posts: 806
    edited 2007-10-10 12:42
    False alarm. The added cap actually did not work. I was misinformed. We're not sure what's causing so much noise and why the cap doesn't help.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔


    The more I know, the more I know I don't know.· Is this what they call Wisdom?
  • deSilvadeSilva Posts: 2,967
    edited 2007-10-10 14:01
    Try to reduce the clock frequency without change of application timing, if possible -> reduced noise?
    Try to increase the clock frequency without changing of application timing (most Propelers work upto 96 MHz (12 MHz x 8 or 6 MHz x 16) -> increased noise?
    Reduce the application timing if possible -> reduced noise?
    Leave out the video - if any -> reduced noise?

    Increase Vdd to 3V6 -> reduced noise?
  • Ken PetersonKen Peterson Posts: 806
    edited 2007-10-10 14:02
    Propeller off and unplugged from power supply - same noise! It's external.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔


    The more I know, the more I know I don't know.· Is this what they call Wisdom?
  • IAN STROMEIAN STROME Posts: 49
    edited 2007-10-10 20:25
    Hi Ken,
    You say it's external noise, my sincere sympathies,
    A good few years ago we were aligning floppy drives in the shadow
    of Portsdown Hill ( Portsmouth UK ).
    We learnt to ignore the pulses from the Navys 100kW+ radar that
    were clearly visisble on the scope when looking for the cats eyes.

    Hope you find a solution, short of a full Faraday cage!!

    Best Regards
    Ian
Sign In or Register to comment.