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Power Supply

Mr Diesel DudeMr Diesel Dude Posts: 13
edited 2010-03-14 03:38 in General Discussion
I've built my first project with the SX chip. It works fine when it is powered by a 9V battery, but I need to install it in a device where a regulated 12V power supply will provide the juice. When I try to power this project from a 12V regulated power supply, it won't run. It is getting 5V (+/- 5 mV) to the Vdd pin in all cases. I've even tried replacing the voltage regulator hoping that might have been the problem. Any ideas?

Comments

  • Martin HodgeMartin Hodge Posts: 1,246
    edited 2010-03-11 04:15
    "it won't run" is a bit vague, but. How do you have the RESET pin wired? make sure you have .1uf filter caps on the VCC next to the chip. Check your GND is making continuity all the way back to your power source.

    Can you provide schematic, pics, code?

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  • Mr Diesel DudeMr Diesel Dude Posts: 13
    edited 2010-03-11 06:47
    I'm using 10 uF caps... is that a problem? I had 1.0 uF caps, but I changed them out only because I've noticed a few commercial designs that I have (one being Parallax's SX Tech board) using the bigger caps (at least on one side of the voltage regulator). I've not tried 0.1 uF caps yet. The code does not seem to be a problem as it works fine on the 9V battery. By the by, what I mean by "won't run" is that the outputs are not doing anything when the SX is attached to the 12V power supply.
  • Martin HodgeMartin Hodge Posts: 1,246
    edited 2010-03-11 17:29
    You really need 0.1uF decoupling cap(s) right at the VDD pin(s) of the chip to filter out noise from the power supply. Those are in addition to the large ones on the vreg. I have no idea if that's what's causing your specific problem, but they are important. Without a schematic or picture of your circuit we can't help you much further.

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  • Mr Diesel DudeMr Diesel Dude Posts: 13
    edited 2010-03-11 19:35
    I hope the attached drawing is adequate. Also, a few additional comments:

    1. The SX circuit does work with the variable voltage power supply. However, it only works from about 7V through 9V. I understand why it starts at 7, but I don't understand why is stops at 9. The regulator is rated up to 32 volts.

    2. I told you previously that the circuit "does not run on the 12V power supply". Actually, it outputs 0 volts on the outputs (Rb 0 on the drawing) most of the time. I was testing it after reading your post yesterday, and on one occasion it actually went to 5 volts on Rb 0. Again, this only happens once the voltage supply (power supply) is increased above 9 volts. Seems like noice could be an issue, but then why would it only become a problem above 9 volts?

    Thanks
    pdf
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    sx.pdf
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  • PJAllenPJAllen Banned Posts: 5,065
    edited 2010-03-11 19:42
    Troubleshoot the power (5V) without the SX.· It has to be wiring and/or a bad regulator.
  • Martin HodgeMartin Hodge Posts: 1,246
    edited 2010-03-11 21:15
    Are you clocking the circuit from the SX-Key? Is it a serial key or a USB key? Have you tried running the circuit with a crystal or resonator with the key disconnected? I have a lot of trouble with the USB key. Sometimes it will output a clock and sometimes not. I always clock my circuits with a crystal or resonator unless I'm using the debug function.

    You don't need the 10K on /mclr unless there's a switch on the line, though it shouldn't hurt being there.

    Is the voltage reg connected to VSS? that's missing on your schematic.

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    -MH
  • Mr Diesel DudeMr Diesel Dude Posts: 13
    edited 2010-03-11 22:19
    I am clocking from the SX key; both serial and USB (I had to replace the serial key last week after I inadvertantly got it connected to 9Vfreaked.gif ). Anyway, it works fine at 9V so I don't think I have a clock issue, and yes, I am running it without the SX key.

    I don't have the voltage reg. connected to Vss. I thought the drawing showed this, but it goes to 12V and to ground, with the output going to Vdd after the 10 uF caps. How should the regulator connect to Vss if other than this?

    ps - thanks for the tip on the mclr. I thought as much, but wanted to make sure.
  • Martin HodgeMartin Hodge Posts: 1,246
    edited 2010-03-12 01:44
    You have me throughly confused now. You say you are clocking from the Key and then you say your not, which is it?

    In your drawing; Vss connects to GND and both caps connect to GND, but VR1 only has two connections. There should be a third pin on VR1 to connect also to GND.

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  • Mr Diesel DudeMr Diesel Dude Posts: 13
    edited 2010-03-12 01:58
    Sorry to confuse you; I may not have understood your question well. To be clear, let's say the SX key is not connected. It programs fine and then it is removed. I am using the internal 4MHz clock of the SX.

    Regarding VR1: my drawing is incorrect. I should have drawn a third pin direct to ground.
  • Martin HodgeMartin Hodge Posts: 1,246
    edited 2010-03-12 02:14
    If you're not making ANY changes to the circuit and just switching from a 9v batt into the vreg, to a 12v source. Then something must be wrong with the 12v power supply.

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    -MH
  • Mr Diesel DudeMr Diesel Dude Posts: 13
    edited 2010-03-12 02:32
    That's what I was thinking, but it is a high end Hewlett Packard. Nonetheless, I cut up some wires and rigged it into my Parallax SX Tech board (the one that says 6 to 9 volts). I cranked it all the way up to 24V and it worked perfect. I think the power supply is OK.
    My project is on a breadboard. Do you think that might be leaking somewhere?


    Thanks for any continued ideas.
  • Martin HodgeMartin Hodge Posts: 1,246
    edited 2010-03-12 03:20
    Out of ideas, sorry.

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  • RobotWorkshopRobotWorkshop Posts: 2,307
    edited 2010-03-12 15:09
    According to your schematic you have the same +12V source powering some other things. You don't list part #'s so we don't know exactly what those are. When you are powering the circuit at 9V are the rest of them powered by 9V too??

    How do you know the SX28 chip isn't running???? Are you basing that on the rest of your circuit???

    Try connecting an LED (with current limiting resistor) to one of the other unused pins (you have plenty of them available) and add code to toggle it on and off at certain points in your program. You can even add a few of them of you want to monitor several things. That way you can use those to tell if the chip is running. It might be running fine but you just might not be getting the output you expect because the rest of your circuit.

    It is a good practice to use a 10K pull-up resistor on the /MCLR line so I would keep that there. I always install one and you should leave it in place.

    Your comment "but it is a high end Hewlett Packard" is a dangerous one. By saying that it sounds like you've made assumptions that it must be fine and as a result may ignore the possibility that may be the problem and looking elsewhere. To really troubleshoot things NEVER assume anything is good unless you test it and verify it is ok. The things people immediately rule out are often ones that can be the problem.

    What kind of Hewlett Packard power supply is it? Would this be a switching style power supply?? Some of those won't work properly unless there is a load on them. Your circuit shouldn't take much power at all and for some switching supplies it may not be enough of a load.

    Just a few more things to look at.

    Robert
  • Mr Diesel DudeMr Diesel Dude Posts: 13
    edited 2010-03-12 20:24
    Thanks Robert,

    Also thanks to Shmoopy and·PJ for the really great advise. You guys all provided the "where to look". It is just tuff looking at problem that you created yourself and actually "seeing" it. You know what they say, "you need another set of eyes"... to proof your work.

    At the risk of being labeled an idiot, I want to tell you what the problem turned out to be, as I feel I owe this to you guys and the community.

    While I drew the schematic correctly, I inadvertanly pulled the MCLR pin up to supply voltage instead of Vdd. I guess the SX can handle up to about 9V on this pin before it quits working. No damage done to the chip though, and I'm sure I·applied at least 14V to this pin.


    One last problem if you have any input: The debug screen does not work properly. It displays, but the area where you can "step", "walk", "run" is always greyed out. However, when I developed this on the SX Tech board, the debug screen works perfect... it is only on the in system version that I have a problem. I am pretty certain that all of the voltages are correct this time.

    Thanks
  • RobotWorkshopRobotWorkshop Posts: 2,307
    edited 2010-03-12 21:13
    Glad to hear that you were able to get everything sorted out. Everyone makes mistakes sometimes and it is easy to overlook things. The SX28 is a pretty robust little chip and I know that one survived an accidental connection to 12V for a short time.

    To confirm that the SX28 chip if fine do you have another one that you can substitute in your circuit or can you move it back to the SX28 Tech board to see if the debug is still grayed out?

    Also, you mentioned you have both the Serial and USB SX-key. Have you tried both? If you are using the USB version of the SX-Key do you have the latest software? It is posted on the Parallax site along with the USB SX-Key. My USB Key acted weird until I updated the software.

    Those options are usually grayed out when you leave a resonator connected in your circuit. The resonator can be left in place for programming but must be removed for debugging. Since you aren't using a resonator (at least from the schematic) I doubt that is the problem.

    For me the debug the Serial version of the SX-Key is usually more forgiving. For that you'll need to supply 5V from your circuit to power the SX-key.

    Robert
  • Martin HodgeMartin Hodge Posts: 1,246
    edited 2010-03-12 21:46
    The USB key does not like proto boards solderless breadboards at all. Sometimes debug works and sometimes not. Glad you got it working.

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    -MH

    Post Edited (Shmoopy) : 3/13/2010 12:18:32 AM GMT
  • Mr Diesel DudeMr Diesel Dude Posts: 13
    edited 2010-03-12 23:00
    I burned my parallel SX key up. It too·got plugged into 9V. Bummer.cry.gif Apparently it is not forgiving like the SX chip. First thing I did once I got the new SX key was to load 3.3.0 software, so yes, it is the most current. No resonator is installed. And now that I think of it, I think the parallel version worked fine on the proto board (debugging and all). I have tried the SX chip (the one with the high applied voltage). It works perfect, debug and all, in the SX Tech board. So..., this only leaves the USB SX key or the proto board. Maybe I should start a new post?
  • Martin HodgeMartin Hodge Posts: 1,246
    edited 2010-03-13 00:15
    Sorry, I meant to say solderless breadboards give problems with the USB key and debug. I use the pre-soldered SX proto boards with no problems.

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  • Mr Diesel DudeMr Diesel Dude Posts: 13
    edited 2010-03-14 03:38
    Thanks Shmoopy. That too is what I noticed, and it was really bugging me. I guess I'll just need to work around this short coming on solderless boards.
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