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Basic Stamp suddenly stops working — Parallax Forums

Basic Stamp suddenly stops working

PatriciaPatricia Posts: 4
edited 2011-10-06 14:56 in BASIC Stamp
I am using the BS2p24 and BS2 to run a data telemetry board. Every once in a while, the basic stamps stop responding. I pop in a new one and it works, but somehow the other stamp has died. Not sure what I am doing to them, sometimes a certain stamp will run forever with no problems, others just stop all of a sudden after working well for weeks or months.

I am powering the board from a 24 V DC supply that is regulated to 5V by a LM7805. Once I sent the stamps back to Digikey where I ordered them and they said there was nothing wrong with them. Every once in a while a stamp that has gone "bad" will come back. It will have stopped being identified by the software, and when I put in a different stamp that one is identified with no problem. I will label the bad one, check it again using the BOE board, and still no identification. But I will put in on a shelf for a month and it will work again. On other occasions the same stamp will be dead forever.

When I run the identification on the software, the Loopback and Echo says: Yes on both. The only thing I could think of is that the power is low and the ones that come back to life are finally getting the right power. As for the ones that stay dead forever, I'm not sure how I killed them.

Any advice would be helpful. I've attached a pdf of the schematic.
pdf
pdf
subsea_v8_s2 Model (1).pdf
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Comments

  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2011-10-06 13:33
    A couple things come to mind:

    1. You're supplying your regulated +5V to the Stamp's Vin pin, which needs at least +5.5V for proper operation. The +5V should go to the Vdd pin instead.

    2. Your schematic doesn't specify what kind/size caps you use on the regulators. Can you elaborate?

    -Phil
  • PatriciaPatricia Posts: 4
    edited 2011-10-06 13:58
    They are 0.33 uF. I took the stamp off that failed last time and put it on the BOE board and checked it with 7V and 9V on VIN with a lab power supply and still got nothing. Then I put in a new stamp and it worked fine.
  • Mike GreenMike Green Posts: 23,101
    edited 2011-10-06 14:23
    You should put a call in to Parallax Tech Support. They'll probably have you send in the Stamps to try to figure out what's happening. What you're observing doesn't make sense. The 78xx regulators are pretty robust and there's not a requirement for any particular capacitors on it. The use of the +5V Vin connection is a potential problem in that the Stamp's built-in regulator, even though low drop-out, does drop at least 1/2V and that gets Vdd dangerously close to the point where the Stamp will reset and stay in reset. That should go away if you put the Stamp in a Board of Education with at least a +7V supply, but that's not what you're seeing.

    Make up a complete schematic of your setup and either post it here or at least send it to Parallax Tech Support.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2011-10-06 14:56
    A lot will also depend on the signals coming in on that 12-pin connector. Since you don't provide any protection to the Stamp pins, if any one of them has a high-voltage or negative-going glitch, it could fry the Stamp.

    Also pursuant to the Vin/Vdd issue (but probably not relevant to the Stamp burning out), your ADCs are not both powered the same. On one, Vcc and Vref come from the Stamp's Vdd output, which will be too low; on the other, Vcc comes from +5V and Vref from Vdd.

    -Phil
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