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1st soldered project having problems... — Parallax Forums

1st soldered project having problems...

JedJed Posts: 107
edited 2008-03-20 02:58 in BASIC Stamp
Ok, I'm soldering up my first prototype. I've got most of the connections made so I decided to test the board. I'm running a simple program as a test that will cycle through the 7-seg LEDs. The program works on the BOE, and I've also verified that the LEDs light if I manually connect wires from the BOE's output pins to my soldered project's LEDs, but for some reason when I pop the chip into the prototype nothing happens. I'm at a loss. I've attached a shot of the front of my board and the back as well as schematic. I mirrored the back to help see where connections are going. Does anyone have any idea why I'm having problems here? I know the back of the board is a bit messy (1st attempt at soldering), but I've verified through a magnifying loupe that there are no shorts on the backside. (there are some areas on the photo that look like shorts but it's just the wires sticking out on a diagonal angle).

Also, one other thing I've noticed: On my power connection. If I have the power switch set to off, then plug the power in, then unplug the power and then turn the power switch on, the power's LED lights up for a few seconds. Does the type of power switch I'm using have a cap or something built into it?

Post Edited (Jed) : 3/20/2008 1:24:49 AM GMT
front.jpg
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back.jpg
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pdf
pdf
Circuit Design.pdf
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Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2008-03-19 15:37
    1) Maybe you have the power switch wired incorrectly. If the large input capacitor is on the power supply side of the switch, then it will act as a battery for a short time when you turn the switch on.

    2) If your program works on a BOE, then it should work on the prototype if that is wired correctly. You really have to start with your schematic and trace through everything all over again. Perhaps you can get someone else to look at it for you (the pictures are not adequate for this) while you go through the schematic and call out the expected connections.
  • JedJed Posts: 107
    edited 2008-03-19 15:40
    On the power switch, it's charging the caps even if I do not turn the switch on at all (until the power is disconnected). So it goes like this:

    I turn the switch off, THEN plug the power in, remove the power, THEN turn the switch on and I get a momentary current.
  • Mike GreenMike Green Posts: 23,101
    edited 2008-03-19 16:21
    Like I said, you probably have the board wired differently from your schematic and there's a capacitor on the input side of the switch. I've never heard of a switch with a capacitor included within it. There are some AC outlet / filter / switch combinations, but they're sold as a combination unit.
  • Mike GreenMike Green Posts: 23,101
    edited 2008-03-20 00:25
    Jed, you mention a power LED. That's not on your schematic. What else is different between what you posted earlier and what you actually have?
  • JedJed Posts: 107
    edited 2008-03-20 00:52
    You're right, I added the LED at the last minute. Sorry about that! I added it to the schematic and reuploaded the file to the original post. So, here the other differences from my schematic:

    I/O Pins 9, 10, 11, 13, 14, & 15 are not wired yet (I wanted to test it first once I got the LEDs in there)
    the reset pin is not wired yet. (normally floats if I'm not mistaken)

    Those should not cause this problem though should they?

    I'm going to go through with a multimeter and check for shorts tonight. Visually I can't see anything wrong with the way it's wired, but maybe I've got a bad solder joint or something. Power is getting to the power LED which is placed on the regulated side of power so I know that's not my problem. Is the cap between Vcc and vss on the stamp ok?

    Post Edited (Jed) : 3/20/2008 1:26:40 AM GMT
  • JedJed Posts: 107
    edited 2008-03-20 01:40
    OK... I just measured voltage across the vss and vcc pins of the stamp and I'm only getting ~3.8V Could that be my problem, and if so why would I be getting less that the regulated output? Could my regulator be bad?
  • roboman01roboman01 Posts: 5
    edited 2008-03-20 02:47
    I had a very similar problem recently with a LM2940 Voltage regulator. The PCB for my science fair project is my second try at a circuit board for this, and when it didn't work, I tried to salvage the voltage regulator parts, but accidentally fried the LM2940 by holding my soldering iron on it too long.
  • JedJed Posts: 107
    edited 2008-03-20 02:53
    It's very possible that I fried it, like I said this is my first try soldering and the power supply was the first thing I soldered. I'll try replacing it and see if that fixes the issue.
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2008-03-20 02:58
    You should go about this in stages, the "one felled swoop" approach is a loser for a first project.·

    Start with the PS, verify; then wire the power to the Stamp, verify; then add the LED circuitry, verify.
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