3.3V Regulator question

I cannot get one of my pcb's to communicate with the Parallax serial terminal. I swapped out the Prop because it's socketed. I removed the crystal oscillator. I tested that Propeller on a different pcb and a breadboard. They worked fine. The 3.3V regulator on the offending board delivers 3.284 volts. Before I desolder it (I don't want to damage traces unnecessarily) is that a likely cause of my problem?
Larry

If the grass is greener on the other side...it's time to water your lawn.

Comments

  • 20 Comments sorted by Date Added Votes
  • Peter JakackiPeter Jakacki Posts: 6,517
    edited February 11 Vote Up0Vote Down
    lardom wrote: »
    I cannot get one of my pcb's to communicate with the Parallax serial terminal. I swapped out the Prop because it's socketed. I removed the crystal oscillator. I tested that Propeller on a different pcb and a breadboard. They worked fine. The 3.3V regulator on the offending board delivers 3.284 volts. Before I desolder it (I don't want to damage traces unnecessarily) is that a likely cause of my problem?

    Com'on Larry, 3.284 volts, you sure it wasn't only 3.28369045 volts :)
    I'm sure there are regulators around that deliver precisely 3.3V but precision has to be measured with precision instruments in a precise way anyway. Think expensive here. 1.5V batteries aren't 1.5V.

    Datasheets specify tolerance for all components, even a 10K resistor would typically have a 1% or even 5% tolerance too. The Prop itself will work quite happily with 3V or less depending upon the temperature and frequency etc. This is normal.

    Always check the most obvious rather than the least probable such as crystals. Will your Prop blink an LED? If yes, then transmit serial data in a test loop and try serial terminal etc. If no, then run blinky in RCFAST, if that works, then it might be a blown PLL or in some cases lack of decoupling caps close to the pins etc. Always check the basics because if you go ripping up the board you will cause problems. Like a Doctor think "do no harm".
    Tachyon Forth - compact, fast, forthwright and interactive
    useforthlogo-s.png
    TACHYON DEMONSTRATOR
    Brisbane, Australia
  • Tracy AllenTracy Allen Posts: 6,082
    edited February 11 Vote Up0Vote Down
    Is this a board you built yourself? Is it one that used to work and then stopped working? There are some basic troubleshooting questions that need to be conveyed.

    No, it is not the 3.3V regulator. But that is an excellent first bit of troubleshooting information. Always check the power supply first!
  • Do you have another prop board you can try. Or is it in your serial terminal object. And are you using a prop plug
  • Always check the most obvious rather than the least probable such as crystals. Will your Prop blink an LED? If yes, then transmit serial data in a test loop and try serial terminal etc. If no, then run blinky in RCFAST, if that works, then it might be a blown PLL or in some cases lack of decoupling caps close to the pins etc. Always check the basics because if you go ripping up the board you will cause problems. Like a Doctor think "do no harm".
    The pcb was the third of three custom boards that I ordered from ExpressPCB. The other boards had no problems. I'm going to put this board aside until I can replace my scope.
    From this point forward everything gets tested on a breadboard before I solder it.
    My project is still being prototyped so I'll just solder a working circuit onto a pcb perfboard.
    DigitalBob wrote: »
    Do you have another prop board you can try. Or is it in your serial terminal object. And are you using a prop plug
    The serial terminal is OK. I tested an identical pcb and I swapped both Propellers. I also have a Prop setup in a breadboard which had no problems. I also have two Prop plugs and they both work.

    Larry

    If the grass is greener on the other side...it's time to water your lawn.
  • Larry, did you load a simple LED blinky into it, even just into RAM, and even just with RCFAST. It shouldn't be necessary to check components or breadboard it and loading in a simple Spin program takes less time than soldering a single component.
    Tachyon Forth - compact, fast, forthwright and interactive
    useforthlogo-s.png
    TACHYON DEMONSTRATOR
    Brisbane, Australia
  • lardomlardom Posts: 1,388
    edited February 13 Vote Up0Vote Down
    Larry, did you load a simple LED blinky into it, even just into RAM, and even just with RCFAST. It shouldn't be necessary to check components or breadboard it and loading in a simple Spin program takes less time than soldering a single component.
    What I did was test every i/o pin with this:
    pub n
        dira[0..31]~~
        repeat
           !outa[0..31]
           waitcnt(clkfreq/20+cnt)
    

    If you look at the photo you will see why the problem bothers me...the pcb is simple. It shouldn't be hard to find what the problem is. The two top boards are good. I tested them with the serial terminal and commented out the CON block. Of course I got garbage but at least they communicated with the serial terminal.
    The two pcb's on the left came from ExpressPCB. I have three of them. The first one is in the controller of my first propeller project. That project is the one you helped complete years ago. (I think that was back in 2009.) The one top left comes out of a mobile robotic arm with pan/tilt for a camera that I built last year. It is very reliable. The pcb bottom right is a Schmartboard which failed and is why I decided to use the board on the bottom left.
    3072 x 2304 - 2M
    Larry

    If the grass is greener on the other side...it's time to water your lawn.
  • I see the bad board is now stripped. I would check for broken traces. Then rebuild starting will the power regulators. Power it up with no prop and check the power pins at the dip 40 locations. Then add components step by step and check power pins
  • Peter JakackiPeter Jakacki Posts: 6,517
    edited February 13 Vote Up0Vote Down
    It looks like the faulty PCB never even had any bypass caps fitted. The pads are too clean.

    I would not have a pcb pulled apart like this. Just put it back together the way it is supposed to be, with the bypass caps but add an LED + resistor to the SCL line to Vdd. This should flash moments after boot if it is trying to read from the EEPROM. You can also flash that same line for test code since the SCL line isn't normally used after boot.

    btw, BIG electrolytics are NOT better than ceramic bypass caps or small tantalums. The electrolytics are effectively useless due to their high ESR at the frequency that the regulator and Prop needs it most. Great for bulk filtering but no good for fast transients.
    Tachyon Forth - compact, fast, forthwright and interactive
    useforthlogo-s.png
    TACHYON DEMONSTRATOR
    Brisbane, Australia
  • DigitalBob wrote: »
    I see the bad board is now stripped. I would check for broken traces. Then rebuild starting will the power regulators. Power it up with no prop and check the power pins at the dip 40 locations. Then add components step by step and check power pins
    I stripped and tested the components on a breadboard and they worked.
    I will keep working on it but I told the person that I'm prototyping this for that I should be able to post an unlisted video so he could see what I've done so far. I'm going to pick up another socket for the Propeller tomorrow and rebuild the circuit on a perfboard.
    Larry

    If the grass is greener on the other side...it's time to water your lawn.
  • It looks like the faulty PCB never even had any bypass caps fitted. The pads are too clean.

    I would not have a pcb pulled apart like this. Just put it back together the way it is supposed to be, with the bypass caps but add an LED + resistor to the SCL line to Vdd. This should flash moments after boot if it is trying to read from the EEPROM. You can also flash that same line for test code since the SCL line isn't normally used after boot.

    btw, BIG electrolytics are NOT better than ceramic bypass caps or small tantalums. The electrolytics are effectively useless due to their high ESR at the frequency that the regulator and Prop needs it most. Great for bulk filtering but no good for fast transients.
    You are absolutely right. My other two boards have those caps but I 'reasoned' that my breadboard setup doesn't have them so maybe they weren't that important so I didn't solder them in.
    An LED on the SCL line sounds great. I'll work on it tomorrow, thanks.

    Larry

    If the grass is greener on the other side...it's time to water your lawn.
  • You've been going in with a microscope when you really needed to be standing back and looking at the big picture. Always be methodical, don't "not bother" especially when that bother is less than a minute's worth. If your regulator had decent capacitors such as ceramic or tantalum and you had ceramic caps on the Prop then I can't see why it wouldn't work. The board is very simple so there shouldn't be any problems with it.
    Tachyon Forth - compact, fast, forthwright and interactive
    useforthlogo-s.png
    TACHYON DEMONSTRATOR
    Brisbane, Australia

  • It looks like the faulty PCB never even had any bypass caps fitted. The pads are too clean.

    I would not have a pcb pulled apart like this. Just put it back together the way it is supposed to be, with the bypass caps but add an LED + resistor to the SCL line to Vdd. This should flash moments after boot if it is trying to read from the EEPROM. You can also flash that same line for test code since the SCL line isn't normally used after boot.

    btw, BIG electrolytics are NOT better than ceramic bypass caps or small tantalums. The electrolytics are effectively useless due to their high ESR at the frequency that the regulator and Prop needs it most. Great for bulk filtering but no good for fast transients.
    Bad crystal. I scavenged the crystal from the failed Schmartboard. I resoldered the components including the bypass caps at your suggestion. I got nothing from the serial terminal but this time I commented the CON block and I got garbage.
    Life is good again. Thank you.
    Larry

    If the grass is greener on the other side...it's time to water your lawn.
  • Cluso99Cluso99 Posts: 12,738
    edited February 14 Vote Up0Vote Down
    lardom wrote: »
    Larry, did you load a simple LED blinky into it, even just into RAM, and even just with RCFAST. It shouldn't be necessary to check components or breadboard it and loading in a simple Spin program takes less time than soldering a single component.
    What I did was test every i/o pin with this:
    pub n
        dira[0..31]~~
        repeat
           !outa[0..31]
           waitcnt(clkfreq/20+cnt)
    

    If you look at the photo you will see why the problem bothers me...the pcb is simple. It shouldn't be hard to find what the problem is. The two top boards are good. I tested them with the serial terminal and commented out the CON block. Of course I got garbage but at least they communicated with the serial terminal.
    The two pcb's on the left came from ExpressPCB. I have three of them. The first one is in the controller of my first propeller project. That project is the one you helped complete years ago. (I think that was back in 2009.) The one top left comes out of a mobile robotic arm with pan/tilt for a camera that I built last year. It is very reliable. The pcb bottom right is a Schmartboard which failed and is why I decided to use the board on the bottom left.

    Your test code is going to conflict with your serial port (propplug) and the eeprom.

    Try dira[0..27] instead of dira[0..31]

    Change waitcnt(clkfreq/20+cnt) to waitcnt(clkfreq+cnt) and the flash will be much slower (1s on , 1s off). You are going to miss seeing 1/20th second.

    Leaving out the bypass caps is often the cause of blowing the PLL in the prop - then the crystal oscillator fails.
    My Prop boards: P8XBlade2, RamBlade, CpuBlade, TriBlade
    Prop OS (also see Sphinx, PropDos, PropCmd, Spinix)
    Website: www.clusos.com
    Prop Tools (Index) , Emulators (Index) , ZiCog (Z80)
  • Cluso99 wrote: »
    lardom wrote: »
    Your test code is going to conflict with your serial port (propplug) and the eeprom.

    Try dira[0..27] instead of dira[0..31]

    Change waitcnt(clkfreq/20+cnt) to waitcnt(clkfreq+cnt) and the flash will be much slower (1s on , 1s off). You are going to miss seeing 1/20th second.

    Leaving out the bypass caps is often the cause of blowing the PLL in the prop - then the crystal oscillator fails.
    I only use this code like this with an LED and a jumper to quickly check all my i/o pins:
    pub n
        dira[0..31]~~
        repeat
           !outa[0..31]
           waitcnt(clkfreq/20+cnt)
    
    Thanks for the tip. I now see the importance of bypass caps.
    Larry

    If the grass is greener on the other side...it's time to water your lawn.
  • The good news is that all the same components work on the breadboard. So look at the PCB's artwork on your computer and check all of your traces to make sure everything is wired right. And add those bypass caps like everyone else already mentioned You can solder those underneath to the pins if you have to. When you get it working see if your spin software works by hitting F7 to id prop.
  • DigitalBob, my education is ongoing. A number of people on this forum are 'rock stars' in my view. I was amazed that Peter noticed that "The pads are clean...".
    The 'details' are important and I should never allow myself to get careless.
    Larry

    If the grass is greener on the other side...it's time to water your lawn.
  • This is true lots of great minds on the forum. You have johnny mac, peter, duane, tom Crawford, wba, heater, (chime in if I missed you)just to list a few. But I would like to think the focus of the forum is for the novice first. It might be someone's first time around any electronics. So I try to explain like I was looking at my board with a bug. Sometimes I overlook simple mistakes on my own projects.
    So I hope you figure it out
  • Cluso99Cluso99 Posts: 12,738
    edited February 15 Vote Up0Vote Down
    When you have been designing hw, pcbs and programming for decades, it is hard to focus on the basics. Trying to explain is harder now because those basics are now ingrained and automatic.

    Just like you trying to remember how you learnt to talk. You forget you initially made sounds like the words your parents made. Gradually you put some words together. They were gramatically deficient but you got your point across anyway. Then you learnt to talk in proper sentences. Now the words and sentences come automatically and you've long forgotten how you learnt to do that, until you see parents with young children learning to talk. This is where I am at with my grandchildren (ages 1-8).

    So back to electronics, we just say put bypass caps here. Its automatic for us oldies. We learnt that if you didn't decouple every IC and a sprinkling of tantalums, you were just asking for trouble. Some of us learnt the reasons while others just took those requirements from others who knew. Now those ICs are embedded into a big chip such as a micro, and those bypass caps become so much more important.

    It is great to grab a new chip (PIC32xxx comes to mind) where the brief technical details show a single cap plus power/ground. No details as to how the power supply should be built (that is assumed). These days anyone can build a simple board and power supply. If it works once, then they assume that it will always work fine. But it isn't always the case!

    Fortunately these days we rarely have to worry about how IC fan-out / loading, etc.

    The point of this is that we often give advice, but we are in a hurry, so we don't take the time to explain why, or we have forgotten that others may not understand why. So, listen to the advice, and if you don't understand the why just ask. There are plenty of us that will take the time to explain the why, and you become better for the understanding.
    My Prop boards: P8XBlade2, RamBlade, CpuBlade, TriBlade
    Prop OS (also see Sphinx, PropDos, PropCmd, Spinix)
    Website: www.clusos.com
    Prop Tools (Index) , Emulators (Index) , ZiCog (Z80)
  • Cluso99 wrote: »
    ...if you didn't decouple every IC and a sprinkling of tantalums, you were just asking for trouble. Some of us learnt the reasons while others just took those requirements from others who knew. Now those ICs are embedded into a big chip such as a micro, and those bypass caps become so much more important.
    ...If it works once, then they assume that it will always work fine. But it isn't always the case!

    ...So, listen to the advice, and if you don't understand the why just ask. There are plenty of us that will take the time to explain the why, and you become better for the understanding.
    The fact that such intelligent people are willing to spend time to share their knowledge is not to be taken lightly. I've gained a ton of valuable knowledge here.
    Larry

    If the grass is greener on the other side...it's time to water your lawn.
  • lardom wrote: »
    Cluso99 wrote: »
    ...if you didn't decouple every IC and a sprinkling of tantalums, you were just asking for trouble. Some of us learnt the reasons while others just took those requirements from others who knew. Now those ICs are embedded into a big chip such as a micro, and those bypass caps become so much more important.
    ...If it works once, then they assume that it will always work fine. But it isn't always the case!

    ...So, listen to the advice, and if you don't understand the why just ask. There are plenty of us that will take the time to explain the why, and you become better for the understanding.
    The fact that such intelligent people are willing to spend time to share their knowledge is not to be taken lightly. I've gained a ton of valuable knowledge here.
    Excellent!

    In computers/electronics, progress is so fast that your always learning. I too have learnt a lot on the forums from others willing to share their knowledge. One never know everything - there's always something more to learn ;)

    And it seems to me that the medical field is advanceing way faster than the computers/electronics industry!

    My Prop boards: P8XBlade2, RamBlade, CpuBlade, TriBlade
    Prop OS (also see Sphinx, PropDos, PropCmd, Spinix)
    Website: www.clusos.com
    Prop Tools (Index) , Emulators (Index) , ZiCog (Z80)
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