Please help me by checking my circuit diagram

Hiya Propeller Community,

Well I'm back again,
I've finally completed (or think I've completed my circuit)

But I feel sure it is missing some capacitors or resistors or something

So I would be really greatful if anyone could check the circuit and tell me where I have issues with it,

I would hope to build a PSU for it later on,
and in the mean time simply power it from my 2A mobile phone charger USB plug thing


Thank You.


Jaan

PS the SVG file attachment was not allowed
so i have zipped it up and you will need to unzip it.

Comments

  • 16 Comments sorted by Date Added Votes
  • Looks good to me. But why don't you through in a VGA plug. And is there any switch in the SD card holder
  • I see only different VGA mode choices. No 15 pin plug with resistors
  • Don't forget those bypass caps close to the pins 0.1uf for all IC's
  • And a bypass capacitor between both Vdd pins and ground (Vss) on the propeller chip.
    In science there is no authority. There is only experiment.
    Life is unpredictable. Eat dessert first.
  • Peter JakackiPeter Jakacki Posts: 6,315
    edited March 9 Vote Up0Vote Down
    If you save your schematic in PNG or JPG format you can just insert the image via the attach tool rather than zipping.

    Anyhow, a few notes:
    1) SD cards include a pullup internally on CS, this is used for card detection so there is never any need for a pullup on this line as it prevents this simple option from being used.

    2) Actual PS/2 sockets aren't necessary unless you are actually interfacing a very old keyboard with actual PS/2 connectors. Modern PS/2 compatible devices come with a passive and bulky gender bender but if you use USB sockets on your board you can plug in directly and the device will detect that PS/2 interface is active due to pullups on both lines.

    3) LM386 chips are so 70's and there are much simpler bridge and class D devices that don't need all those bulky electrolytics. Plus the new devices can give you 5W from 5V whereas the LM386 is very weak at this voltage.

    4) Your bypass caps are only as good as their position and "goodness" of the connections. Short and straight to the point, that's how they need to be, especially if you run at 96MHz.

    5) Some people may still use old HC49 crystals for their designs but at 6MHz you can get anything you want, even in through hole. Besides SMD I also use miniature cylindrical "watch" crystals that are even cheaper than the HC49s. The other reason for using a smaller crystal is that you can reduce the track length from the Prop and keep this part of the circuit tight and noise free. This also means you can connect your bypass cap very close where it needs to be.

    6) Keep the track to the reset switch well guarded, don't just have a long skinny track snaking its way over noisy signals or ready to receive radio Moscow.

    7) An I2C RTC would be much better as it can sit on the same lines as the EEPROM. However you should always have a suitable series resistor if you are using a battery. A value of around 1K is fine.

    * I didn't think I'd be finding this many points to post about.

    9) Don't even bother with a 24lc256 32k EEPROM. Spend another 20 cents and treat yourself to a 64k device such as a M24512 etc. Then you can store stuff safely in the top 32k etc.

    10) SCL should have a pullup for more general-purpose use as some drivers expect it. I also like to include in addition an LED + resistor from Vdd as a status and boot indicator.

    Ok, I've had enough now but this advice is not specifically for you though as it applies to any design.
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  • DigitalBob wrote: »
    Looks good to me. But why don't you through in a VGA plug. And is there any switch in the SD card holder
    I see only different VGA mode choices. No 15 pin plug with resistors
    Don't forget those bypass caps close to the pins 0.1uf for all IC's

    Hiya Digital Bob,
    Thank you for your help,
    I do have a VGA connector,
    Apologies for not making it clear.
    I bought one from Parallax
    And in my haste to get things ready,
    I made a fatal mistake and did not line up the pins/wires properly with the holes on the PCB
    And it was only when I switched the thing on that I saw a wisp of smoke come from the VGA PCB board.
    And here's me thinking my soldering wasn't bad...
    To remedy this I bought another one from ebay (already soldered) and that works great
    although it only has one PS2 port on it

    Sorry for my green-ness...
    But what do you mean by bypass caps close to the pins 0.1uF for all IC's?
    Do you mean this in reference to the VGA connector? or the Propeller1 chip?

    Jaan

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  • PS
    I will check the SD Card holder to see if it has a CD switch n it when I dig it out of storage over the weekend and get back to you.
    Though I presume if it doesn't have one then I am left with one more FREE pin on the MCU.

    Jaan
  • lardomlardom Posts: 1,371
    edited March 9 Vote Up0Vote Down
    DigitalBob, kwinn, and Peter Jakacki I won't hijack this thread but I am listening. I've heard this several times: 0.1uf bypass caps near all ic's.
    I just put together a basic wireless motor driver pcb. The nRF24L01+ operates @2.4Ghz and the L293 @20Khz pwm. (and the Prop runs @ 80Mhz) The pcb is supplied with 3.3V, 5V and 6V. If I had a scope I'm sure I would see noise.
    Larry

    If the grass is greener on the other side...it's time to water your lawn.
  • kwinn wrote: »
    And a bypass capacitor between both Vdd pins and ground (Vss) on the propeller chip.


    Hiya KWinn,

    MMMMMmmm I thought the caps I've highlighted in the pink circles were those ones?
    Maybe the size of them is right? the uF size?
    Or maybe they need to be polarised?.

    2805 x 2019 - 164K
  • If you save your schematic in PNG or JPG format you can just insert the image via the attach tool rather than zipping.

    Anyhow, a few notes:
    1) SD cards include a pullup internally on CS, this is used for card detection so there is never any need for a pullup on this line as it prevents this simple option from being used.

    2) Actual PS/2 sockets aren't necessary unless you are actually interfacing a very old keyboard with actual PS/2 connectors. Modern PS/2 compatible devices come with a passive and bulky gender bender but if you use USB sockets on your board you can plug in directly and the device will detect that PS/2 interface is active due to pullups on both lines.

    3) LM386 chips are so 70's and there are much simpler bridge and class D devices that don't need all those bulky electrolytics. Plus the new devices can give you 5W from 5V whereas the LM386 is very weak at this voltage.

    4) Your bypass caps are only as good as their position and "goodness" of the connections. Short and straight to the point, that's how they need to be, especially if you run at 96MHz.

    5) Some people may still use old HC49 crystals for their designs but at 6MHz you can get anything you want, even in through hole. Besides SMD I also use miniature cylindrical "watch" crystals that are even cheaper than the HC49s. The other reason for using a smaller crystal is that you can reduce the track length from the Prop and keep this part of the circuit tight and noise free. This also means you can connect your bypass cap very close where it needs to be.

    6) Keep the track to the reset switch well guarded, don't just have a long skinny track snaking its way over noisy signals or ready to receive radio Moscow.

    7) An I2C RTC would be much better as it can sit on the same lines as the EEPROM. However you should always have a suitable series resistor if you are using a battery. A value of around 1K is fine.

    * I didn't think I'd be finding this many points to post about.

    9) Don't even bother with a 24lc256 32k EEPROM. Spend another 20 cents and treat yourself to a 64k device such as a M24512 etc. Then you can store stuff safely in the top 32k etc.

    10) SCL should have a pullup for more general-purpose use as some drivers expect it. I also like to include in addition an LED + resistor from Vdd as a status and boot indicator.

    Ok, I've had enough now but this advice is not specifically for you though as it applies to any design.



    Hiya Peter,

    Thank You to you and the other members who have taken the time to study my diagram and assess if it has mistakes in it.

    With reference to your advice:

    I have changed the SVG to a GIF image
    1) SD Card Pull-ups (see apology bellow)

    2) No need for older PS2 type connectors - Use USB instead...
    Thank you I will change the connectors to USB type instead of PS2

    3) Dont use LM386 Audio IC - Use a modern one instead...
    Coming from an engineering/ programming background,
    My electronics skills are non existent and I use common sense (when I can find it)
    Please could you recommend a modern & commonly usedAudio IC for GP audio output use?

    4) Bypass caps & positioning of same...
    So going by your advice,
    I should really have placed them FIRST on my circuit
    rather than LAST as I did when I designed my circuit!
    So close as possible to the pins and solid soldering (no dry joints etc)

    5) Crystals...
    I have the long and thin in steel case crystal from Parallax...
    Should I seek out a smaller cylindrical one? (if it is available?)
    Similar to the one on the RTC module (see below)

    6) Reset switch tracks...
    I think I will use a two wires to the reset switch on case when I make the case
    In the mean time I will just use PCB push button on the pinboard
    (that block/board with all the holes in it - see crystal photo for the board - I forgot its name and call it a pinboard)

    7) Use I2C RTC instead of the one I have...
    I will look into finding an I2C RTC IC,
    this will mean I can use the Eprom pins/wires/lines (is that right?)
    Also freeing up 2 pins at the same time?

    8) Thank you - Yes I am a real beginner in electronics and try to use common sense though its not always enough

    9) Change 24LC256 Ic for M24512....

    10)SCL should have pull up and optional LED to Vdd
    I'm not sure if I have this bit right but have uploaded a new photo with the changes I will make[/b}


    I have excluded making changes to the RTC and SD CARD holder (because these are ready made modules)
    But if they don't work then I will try to make the circuit manually implementing the changes necessary as per everyone's advice


    Finally...


    APOLOGY
    ======
    I feel I have done you all an injustice by not providing enough information.

    Since my days of messing around with Picaxe micro-controllers
    I still have some surplus stuff which I never got around to using,
    And I had intended on using those (if possible)
    To be precise the SD Card holder and the RTC are both ready made modules
    (see photos below)

    So apologies to everyone who has helped me with their advice :)
    These are the modules and crystal I have,



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  • DigitalBob wrote: »
    Looks good to me. But why don't you through in a VGA plug. And is there any switch in the SD card holder

    Yes there is a micro switch which I can hear clicking as the card is inserted/uninserted
    (see photo above?)
  • lardom wrote: »
    DigitalBob, kwinn, and Peter Jakacki I won't hijack this thread but I am listening. I've heard this several times: 0.1uf bypass caps near all ic's.
    I just put together a basic wireless motor driver pcb. The nRF24L01+ operates @2.4Ghz and the L293 @20Khz pwm. (and the Prop runs @ 80Mhz) The pcb is supplied with 3.3V, 5V and 6V. If I had a scope I'm sure I would see noise.

    Hiya Iardom,

    I understand where I went wrong,
    I placed the decoupling caps into my circuit as the LAST components...
    Placing the decoupling caps FIRST would mean they are as close as possible to the IC and not compromised.

    I havn't updated the circuit because i'm using pre-bought modules for the RTC and SD Card
    And also the fact that practically everything except the Prop1 and the power is incorrect in my design.

    But I understand now that decoupling caps need to be as close as possible to the ic...
    As can be seen in my photo below...
    hopefully lol

    And its all a bit moot now because...
    dont laugh but my eprom section looks nothing like the the way it should
    I just saw the power and ground end up together and it shouldnt...

    It should look like the darker coloured circuit at the bottom of this pic.
    Oops

    Gosh what a lot I've learned from this lol


    Jaan


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  • You could look at some of the parallax product schematics like the one for the prop activity board WX or BOE.
  • Thank You Digital Bob,

    Yes I'm doing that again now.
    Hopefully this time round,
    I may see something I missed first time round.

    Jaan
  • This is much better.
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    I know two things for sure.
    1. I don’t know everything.
    2. I do know how to find the answer.
  • Thank You
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