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BS2 Power Problem — Parallax Forums

BS2 Power Problem

skatjskatj Posts: 88
edited 2008-01-18 17:53 in BASIC Stamp
Whenever I make a closed circuit the Stamp's power LED doesn't light up and nothing happens. If I don't ground the circuit, the LED is lit. Any ideas what's wrong? It only just started happening.

Comments

  • FranklinFranklin Posts: 4,747
    edited 2008-01-18 02:24
    sounds like a short to me.

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    - Stephen
  • skatjskatj Posts: 88
    edited 2008-01-18 02:27
    Any way I can fix it?
  • FranklinFranklin Posts: 4,747
    edited 2008-01-18 02:34
    Check your wiring. If you could attach your schematic we could look for obvious errors.

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    - Stephen
  • skatjskatj Posts: 88
    edited 2008-01-18 02:40
    The trouble is, I have no schematic. If I connect a wire straight from Vdd to Vss, the BS2 won't light up.

    edit: Also, when I use a 9V motor (Vdd to Vss), the Stamp works. Strange..

    Post Edited (skatj) : 1/18/2008 2:59:16 AM GMT
  • FranklinFranklin Posts: 4,747
    edited 2008-01-18 04:58
    Read the documentation!!! Vdd to Vss is a short and, no the light will not light. What are you trying to do with the stamp and what are you hooking up. What do you have the stamp plugged into and how are you programming (or planning to program) it?

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    - Stephen
  • skatjskatj Posts: 88
    edited 2008-01-18 05:18
    I'm new to electronics, could you explain the difference between connecting the two motor wires to Vss and Vdd, and just connecting a wire to Vss and Vdd?
  • allanlane5allanlane5 Posts: 3,815
    edited 2008-01-18 17:53
    In order for electronics to work, you need a "voltage difference" between two points. When you connect those points with a resistance, the current that flows is described by the equation "Voltage == Current * Resistance". On the BS2, the voltage is usually 5 volts -- meaning Vdd is at +5 volts, and Vss is at "ground" or zero volts.

    When you put a motor between these two points, current flows and the motor spins. When you put a wire between those two points -- well, another name for wire is "almost zero resistance connection". Now if you had a "perfect" voltage source, one that could supply infinite current at 5 volts, then the wire would try to conduct infinite current. The wire physically can't conduct infinite current without melting -- this is what a fuse does, melt at a certain current.

    Since your voltage source is NOT perfect, when you try to get lots of current out of it, the voltage drops. So what you did with your wire is called "shorting Vdd to ground". It's not something you want to do, ever. Because when Vdd goes to zero, nothing else works.

    Bottom line -- your "closed circuit" MUST have some resistance in it -- a 220 ohm resistor is enough -- so that you don't over-stress your voltage source.· Note the 7805 on the BOE will ONLY give you one amp before IT over-heats.
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