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Propeller Eduacation Kit Labs:Fundamentals (Problem) — Parallax Forums

Propeller Eduacation Kit Labs:Fundamentals (Problem)

dmooredmoore Posts: 4
edited 2013-02-25 08:33 in General Discussion
Hey guys, I'm new to the propeller and I have just started the lab kit, currently on lab 3 setting up at testing the propeller. I've checked all of my wiring many times and it all seems to be correct, and I'm measuring all of the correct DC voltages across everything, however I'm getting 6.5V AC across all of the power/ground connections. In the lab manual it says that the AC voltage should be in the mV and if it's any higher then I should consult page 44(troubleshooting - 11)

My capacitors are connected in the correct sockets, the top one measuring 5V DC (10V AC) and the bottom one measuring 3.3V DC (6.5V AC)
Like I said, all of my DC voltages are still correct, from G3 to any black is only 5V DC, from G1 to any black is 9V DC and any red to any black on the rest of the board is 3.3V DC, but i still have that 6.5V AC every where. Any Help would be much appreciated!

Comments

  • Duane DegnDuane Degn Posts: 10,588
    edited 2013-02-23 11:08
    Could you take a picture of your setup and point out on the picture where you're measuring these voltages?

    Do I understand correctly, that your 5V and 3.3V supplies read correct in the DC mode of your voltmeter but the same supplies read 6.5V when the voltmeter is in AC mode?

    What kind of readings do you get if you use your voltmeter on a battery (in both DC and AC modes)?
  • ElectricAyeElectricAye Posts: 4,561
    edited 2013-02-23 11:09
    What are you using for a power supply?
  • dmooredmoore Posts: 4
    edited 2013-02-23 11:56
    20130223_114957.jpg

    My power supply is the 9V battery and the usb conection is supplying some as well i would assume. And the 6.5 or 6.6V AC is anywhere on the board from power to ground. All of my power connections (Red wires) are coming off of the 3.3V voltage regulator. From the 5V regulator plugged in next to it to ground i am getting 10V AC
    20130223_114957.jpg
    1024 x 768 - 117K
  • dmooredmoore Posts: 4
    edited 2013-02-23 12:00
    Maybe my multimeter is just poor, but everything works correctly. all of the DC voltages are exactly what they should be at every point. I even Downloaded and wired the PushButtonLedTest program into the EEPROM and it worked fine, and I was able to confirm that all of the I/O pins work correctly...
    So i might just be worrying about nothing, but in the lab manual it says that the AC voltage should be around 50mV...
  • Duane DegnDuane Degn Posts: 10,588
    edited 2013-02-23 12:03
    dmoore wrote: »
    So i might just be worrying about nothing,

    I think you're good to go.

    The AC should only be a problem if you're using a wall-wart type power supply. A 9V battery doesn't have an AC component.

    You may want to upgrade your 9V battery to some NiMH AA cells to save on money. You'll also want to use a different battery (or other power supply) if you use a servo. 9V batteries and servos are a problem waiting to happen (the 9V doesn't provide enough current for many servos and will cause the Propeller to reset).
  • dmooredmoore Posts: 4
    edited 2013-02-23 12:08
    Yeah thank you.
    Just started playing with this thing and didn't want to burn anything the first day and have to get a new one haha.
  • ElectricAyeElectricAye Posts: 4,561
    edited 2013-02-23 15:01
    dmoore wrote: »
    Maybe my multimeter is just poor......

    Did you try testing a free-standing battery with your multimeter on its AC setting just to see what it reads? It's very possible that the bad 6 volt AC reading is simply a reading within the cheap multimeter's margin of error. That is, 6 volts/200 volt range is about a 3% error, or 97% accuracy in that given range. I suppose it could also be an artifact of your multimeter's internal battery getting weak, so if you haven't changed the battery in a while, you might see if that gives better results.
  • Oldbitcollector (Jeff)Oldbitcollector (Jeff) Posts: 8,091
    edited 2013-02-23 18:48
    ElectricAye wrote: »
    Did you try testing a free-standing battery with your multimeter on its AC setting just to see what it reads? It's very possible that the bad 6 volt AC reading is simply a reading within the cheap multimeter's margin of error. That is, 6 volts/200 volt range is about a 3% error, or 97% accuracy in that given range. I suppose it could also be an artifact of your multimeter's internal battery getting weak, so if you haven't changed the battery in a while, you might see if that gives better results.

    Actually, I recognize that meter. It's a $5.00 Harbor Freight multimeter. I've got several of them. They come with some rather poor Chinese batteries (at least mine did) I'll second this comment to change the battery and see if your results change.

    Jeff
  • rwgast_logicdesignrwgast_logicdesign Posts: 1,464
    edited 2013-02-23 20:56
    Just to second Duanes comment. I usually use a wal mart wal-wart that is adjustable from 4 to 12vdc and outputs 1.3a. This is the best option when testing stuff on your bench. Since ive gotten in to robotics batteries have become essential. I dont know how many times ive wasted an hour plus debugging issues with robotics because I was being lazy and just used a 9v to powetr my micro controller. They will read 8vs with a meter but wont have any current left, this causes all sorts of issues, motors randomly spinning up, not working at all etc, things that could easily be mistaken for bad code.
  • RDL2004RDL2004 Posts: 2,554
    edited 2013-02-24 05:37
    Does the PE Kit have enough filtering on the power input to cope with unregulated AC adapters? Cheap power adapters (wall warts) can have many volts of ripple. A regulated switch-mode type is much better, but they still often have several hundred millivolts of ripple.
  • rwgast_logicdesignrwgast_logicdesign Posts: 1,464
    edited 2013-02-24 16:09
    Im not sure, I know the adjustable wal warts at wal mart are the regulated switching type, ive tested them before and they do have quite a bit of ripple, even compared to my homemade through hole switchers. I think I remember it being something like 10mv or ripple under load.

    Ive never used a PE-Kit but when I started I basically got all the parts from parallax to bread board my first propeller circuit. I used the 3.3v regulator in the store along with the suggested filtering caps and it filters out the wal warts filter fairly well. I think the three volt regulators use a .1uf and 10uf cap, so if thats what the PE kit uses it should be fine.
  • frank freedmanfrank freedman Posts: 1,983
    edited 2013-02-24 20:58
    I would suggest one of two possibilities. The first is the meter is auto-ranging and the reading may 10mvAC from surrounding noise sources. More likely you have a ground loop between your PEK setup and the pc usb port. Test your connections without the usb plug in and see if the AC component goes away. No way you should be getting >6v let alone AC if you are getting correct dc from your regulators. If it still shows this AC voltage look for a range indication or with another meter to eliminate your meter as an issue.

    Good Luck,

    FF

    [QUOTE=dmoore;1165

    861]
    20130223_114957.jpg

    My power supply is the 9V battery and the usb conection is supplying some as well i would assume. And the 6.5 or 6.6V AC is anywhere on the board from power to ground. All of my power connections (Red wires) are coming off of the 3.3V voltage regulator. From the 5V regulator plugged in next to it to ground i am getting 10V AC[/QUOTE]
  • ZetsuZetsu Posts: 186
    edited 2013-02-25 08:33
    I am very confused as to why we are measuring AC on a DC circuit.
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