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USB to serial question

Discussion in 'General Electronics Discussion' started by peter st, Jan 11, 2014.

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  1. peter st

    peter st

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    Jan 11, 2014
    sorry back again still waiting on my perf boards was just wondering as the ones i ordered are 5cm x 7cm with 1mm holes can they be cut down in size as i dont think i will need them that big and any tips to make it easy as i will be needing to make between 50 and 100 of theese
    thankyou
    peter
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,361
    2,756
    Jan 21, 2010
    Yes, you can cut them.

    First tip is to buy the size you need.

    Second tip is if you need to cut that many, I wouldn't do it with a hand saw.

    If you can leave the board un-cut, you'll save yourself time and effort and also allow you to spread the circuit out more (which is generally a good thing).

    At the very least, build a couple before you cut down the boards just to make sure that it's practical to build them on the smaller board.

    Oh and a third tip is that matrix board has to be the hardest way to make things in quantity.

    I made 4 units of a small controller on matrix board. Whilst the first one (the prototype) was fine, and I got it working well, etc, reproducing it was a pain, and really time consuming.

    I am relieved to find that nobody here recommended matrix board after knowing the quantity you needed to make.

    I'd recommend you build a prototype, then test it. Once you're happy, document what connects to what and where each component goes (with orientation where required). Document from the copper side where connections are made and in what order. Use the leads of through hole components (like resistors) where possible to connect things.

    Then build another one from the instructions and make sure it is identical to the first (and obviously test it)

    Then set up a production line for maybe 10 units. Do step 1 on all of them, then step 2, then step 3, etc.

    With matrix board construction, I'd probably recommend testing each unit, but after producing a batch, check at least one, and bag them up as a batch. If you find any of them have an error, you would be wise to suspect that the entire batch may have the same error.

    Then, make up maybe 60 units in total so that if there are less than 10 failures during testing, you don't have to try to repair and diagnose them.

    If you're planning to make 100, then make the first run of 50 first (that's 2 prototypes plus 60 units. If out of that 60 (the 2 prototypes should be kept as your reference units) you get 55 working units, those extra 5 mean that maybe you need only make 55 (if you're brave 50) to have a similar safety factor.

    Oh and mark each unit with the batch number ant the number within the batch. Record which ones fail testing. If you end up selling, giving away, or having to maintain them, a record of where failures are (a particular batch perhaps?) will be very useful.
     
  3. peter st

    peter st

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    Jan 11, 2014
    i will be selling them but they need to be incorporated into a cable to make it work thank for your advice
     
  4. peter st

    peter st

    30
    0
    Jan 11, 2014
    hi sorry to ressurect my old thread i have a question it is in reference to my cable and im now wondering if i did not need all the circuit here is the owner/creator of the combro which is what my cable connects to from the computor being asked a question and his reply which to be honest i do not understand

    Question been asked to him
    Looking at the Combro info the serial communications runs at 0 to 5v, which means it SHOULD be TTL. Robin will be able to confirm that.

    His reply
    Sort of, it's dual function, here's an explanation for those who do electronics-speak...

    (this bit is all in referenence to the internals of the combro i belive)
    ..it starts at the pin with a 1M resistor pull down and then connects to the processor through a 10k resistor. When you press RST the cb-625 starts by reading the serial pin and if it finds a high it disables the power saving features.

    (and this is in reference to the cable i think )
    To get both the disable and the serial output we apply a 100k pullup in the cable. That gives you 100k up, 1M down and a 10k in series so the 0-6V serial output is, at best, approximate. We sort it out with an op-amp which leeches it's power from the serial port. We get negative volts from the TX pin and the software sets RTS high for the positive.

    (this bit not sure what its in reference to lol)
    cb-625 has to have the 10k in series so you can short the battery back on to the serial pin without blowing the processor when it tries to pull the line low.

    What im after is understanding what he is saying about the cable and if it means i do not need all the circuit i was previously helped with by you good people

    thankyou in advance peter
     
  5. gorgon

    gorgon

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    24
    Jun 6, 2011
    This is related to a standard RS232 port on the PC.

    You wanted to use the USB Device, and you can't use the opamp solution for this.

    If you are using the 2 transistor Circuit I sketched for you, the main question is, does it work as intended?

    Does it disable the Power save, as explained in Your quotes?

    The main thing is, does it work?
     
  6. peter st

    peter st

    30
    0
    Jan 11, 2014
    yes it is working great thankyou gorgon :D
    i was just wondering if i could make it more compact ie reduce the size
    and again many thanks for your help
    at the moment i end up with a perf board about 2.5cm x1.5cm which is part way down the cable which i cover in glue for extra security then heat shrink
    regards
    peter
     
  7. gorgon

    gorgon

    603
    24
    Jun 6, 2011
    You can always make it smaller, using SMD components, but it comes down to cost.

    If you plan to produce a great number of these, you may think of making a small PCB as a part of the plug into the Cobro, then you only need to attach the wires from the USB Device to this PCB and heatshrink it all.

    SMD Components comes in many sizes, from hand solderable, to barely visible.
     
  8. peter st

    peter st

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    0
    Jan 11, 2014
    hi gorgon i have been looking at smd components and i like the look of it how difficult is it to make a pcb from the looks of it 8050's look a easily workable size im realy getting interested in all this now :)
     
  9. gorgon

    gorgon

    603
    24
    Jun 6, 2011
    0805 is ok to handsolder, so is 0603, but for smaler sizes you more or less need to reflow solder it. Transistors in SOT23 is also ok to hand solder.
     
  10. peter st

    peter st

    30
    0
    Jan 11, 2014
    for the size board im wanting to do will i be best using a marky and hand drawing it ?
     
  11. gorgon

    gorgon

    603
    24
    Jun 6, 2011
    It depends on many things. First of all how many boards you need to make and how good you are at making PCBs.
     
  12. peter st

    peter st

    30
    0
    Jan 11, 2014
    how good i am erm never made 1 lol
    how many 50 to start with i guess
     
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