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Building the propeller labs circuit without a 3.3 voltage regulator — Parallax Forums

Building the propeller labs circuit without a 3.3 voltage regulator

noobmunchernoobmuncher Posts: 124
edited 2009-11-28 21:57 in Propeller 1
Hello,

So after about a week of hard core trial and error I have fianlly figured out what is wrong with my circuit (which is the one from the propeller labs manual). Turns out I must have bought the wrong 3.3v voltage regulator or something because that seems to be the only error in the entire circuit. So while I am waiting for a new one, is it possible for me to just use a resistor to take the 5.0v rails and convert it to run the chip?

Thank you!

Comments

  • LeonLeon Posts: 7,620
    edited 2009-11-27 20:42
    No. You could use three diodes, though, to give you a voltage drop of about 1.8 V.

    Leon

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    Amateur radio callsign: G1HSM
  • Toby SeckshundToby Seckshund Posts: 2,027
    edited 2009-11-27 20:51
    Whilst I hav run a prop at 4.2 Volts without any problem, I would be cautious about 5 Volts. The resistor would leave it without much regulation for load changes etc. Light load, few cogs or low frequency would leave the volts high and heavy load, etc would drop the VDD down, pehaps too low. Also the brownout circuit would certainly have an opinion too.

    What was so wrong with your regulator? If it was too low a current output for your load then possibly use an external transistor and feed the load from pre regulator.

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  • noobmunchernoobmuncher Posts: 124
    edited 2009-11-27 22:06
    The problem is that when I tested the 3.3 volts regulator by itself I am only getting like 1.28 volts from it. I have no idea why, it is a 3.3 volt regulator, but yeah I am getting way less then i should.
    Does anyone know why? The 5.0volt regulator I am getting 5.0volts and all I am doing is switching out which voltage regulator I am testing.

    Thanks
  • kwinnkwinn Posts: 8,697
    edited 2009-11-27 22:16
    Either it's a dud or a mislabeled adjustable regulator. Both things happen occasionally.

    PS - Leons diode idea works very well.
  • DonEduardoDonEduardo Posts: 54
    edited 2009-11-27 22:29
    If you've got a Radio Shack nearby you could run out and get an LM317 and a 10K trim pot and dial up any voltage you like. And if that one you have is an adjustable, you'll probably be able to adjust it as well by using the trim pot (or individual resistors if you feel like calculating resistor values).
  • noobmunchernoobmuncher Posts: 124
    edited 2009-11-27 22:30
    Yeah I found it odd because i bought two of the same voltage regulator from digikey (the 3.3volt) and they both give me incorrect outputs. On the note of not being able to use a resistor to regulate power, would it work if I took the power from the 5.0 volt regulator and brought it down to 3.3 volt? Or would it not allow enough load or something.
  • LeonLeon Posts: 7,620
    edited 2009-11-27 22:44
    Check the regulator connections carefully against the data sheet. Have you included the specified capacitors? They can oscillate otherwise, and give an incorrect voltage. I use an LM317 with two resistors for the 3.3V supply on my Propeller boards.

    Leon

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Amateur radio callsign: G1HSM
  • DonEduardoDonEduardo Posts: 54
    edited 2009-11-27 22:46
    The adjustable regulators use a resistive divider to set the output voltage. It's not the same thing as what you had proposed which won't work (well). Basically for adjustable regulators you attach the adjustment pin to the center of a trim pot (at least that's what I do). Here is the datasheet for the LM317

    http://www.fairchildsemi.com/ds/LM/LM317.pdf

    Notice the schematic in figure 5. It shows you how to configure an adjustable regulator. Yours may be configurable the same way because your output voltage is suspiciously close to the output of the LM317 when the adjustment pin is directly connected to ground.
  • noobmunchernoobmuncher Posts: 124
    edited 2009-11-27 22:56
    I don't have an adjustable one though it is a LT1587 and yes i use the required capacitors. However in an attempt to narrow down problems I built a VERY simple circuit to just purely test the voltage regulators and that ended up being where the problems with the project where. I have what I presume to be the correct volatge regulators on order anyhow so they will be here soon.
  • mctriviamctrivia Posts: 3,772
    edited 2009-11-27 23:20
    maybe the pin orientation you are using is wrong. make sure you have in/out/gnd in the right place. many packages use different pin orders or you may just be trying to put in backwards.

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    24 bit LCD Breakout Board coming soon. $21.99 has backlight driver and touch sensitive decoder.
  • DonEduardoDonEduardo Posts: 54
    edited 2009-11-27 23:28
    Yeah, but as kwinn said, yours might be mislabeled. If you want to wait for the new ones you can, but personally I wouldn't have the patience. It sounds like you already have some resistors on hand and those regulators aren't doing you any good right now. The datasheet for the LT1587 shows how to connect up the adjustable version of that chip (which we suspect you might have instead of the fixed one). Grab two equally sized resistors from say 1K to 5K and hookup the circuit like in the datasheet and connect the "GRound" pin in between them instead of to ground. You should get exactly double the voltage you were getting before.

    But then again, it might be better to wait before hooking that up to the Prop because if its a dud it might damage the Prop. The fear of blowing something up unfortunately has never held me back though. I can't rest until I get it working...... or until it blows up, whichever comes first.
  • Graham StablerGraham Stabler Posts: 2,510
    edited 2009-11-28 00:09
    Check for dry joints, particularly on the GND.

    Graham
  • Dr_AculaDr_Acula Posts: 5,484
    edited 2009-11-28 03:26
    I bought 10 regulators recently that were supposed to be 3V and they were actually 8V. Irritating. Lucky I always socket the chips and power up the boards with no chips and just the passives and the supply before going any further otherwise that would have zapped the prop!

    The 3 diode trick from 5V works fine.

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    www.smarthome.viviti.com/build

    Post Edited (Dr_Acula) : 11/28/2009 3:45:52 AM GMT
  • Toby SeckshundToby Seckshund Posts: 2,027
    edited 2009-11-28 09:06
    I "tested" a Prop, with 9 Volts, and it died, so it must have been inocent. Dr_A chickened out on the 8 Volt testings, I have never seen a 7 Volt reg but I do have some 6 V ones, I have no intentions of trying them though, Props are too rare and expensive to pursicute. I did a minimal Blade2 board with no reg on it, all was wonderful, until I did " one quick change " too manyand then pluged in the wrong PSU. The 9 Volts, 2.2Amp PSU didn't suffer at all ( £15s worth of toasted silicon )

    Regs will offer your Prop with a wholesome enviroment, right voltage - held steady, along with a degree of over-voltage and current protection. If the delay isn't too much I would wait for the right component. As Dr_A states, I usually power up the board, and measure, before precious silicon is placed in the way of danger. I have cheated with diodes as Leon says.

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    Style and grace : Nil point
  • DroneDrone Posts: 433
    edited 2009-11-28 13:49
    For a short test, just two fresh (important) 1.5V (e.g. AA) batteries and try powering the Prop from them, this should be close enough to 3.3V with 5Mhz crystal and x16 PLL. Of-course disconnect your regulator etc. first.
  • rjo_rjo_ Posts: 1,825
    edited 2009-11-28 16:49
    I have also tested around 4V... it ran fine (only tested it for a few days ... don't remember exactly). So... you could run off of AAA batteries if you want. Or you could use a voltage divider... but you would need more than a 1/4 watt resistor next to your power input. I like the idea of a variable power supply... seems like a good tool for all kinds of things.

    Don't worry about the Prop... it is practically indestructible. I have burned up several ... but it requires real talent[noparse]:)[/noparse]

    Rich
  • LeonLeon Posts: 7,620
    edited 2009-11-28 16:56
    I put about 9V across one yesterday - caused by a solder splash across two regulator pins. It didn't survive the experience.

    Leon

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    Amateur radio callsign: G1HSM
  • rjo_rjo_ Posts: 1,825
    edited 2009-11-28 16:57
    Sometime around the intro of the PropII I want to throw a free dinner for everyone who has fried a Prop and give out awards for the most creative story[noparse]:)[/noparse]
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2009-11-28 17:49
    A free dinner?·

    Will it be a fry-up then?
  • DonEduardoDonEduardo Posts: 54
    edited 2009-11-28 21:57
    18 volts last week. I'm building a universal smart battery charger and hooked up my 18 volt drill battery. A couple of exposed wires wound up where they shouldn't have. Fried both the prop and an LCD display. Luckily I buy at least two of everything when I order. Swapped out the LCD and Prop in a few minutes. Prop was socketed. Parallel LCD unfortunately was all soldered up...16 tiny little connections.

    That's one reason I left electronics while in high school and switched over to software (programming). You can write a lot of really bad code and still not fry the computer. Although I suppose bugs in SPIN could fry things if you get inputs and outputs crossed. Haven't run into that yet.
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